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<bibtex> @article { 484, title = {Security Analysis of Wireless Mesh Backhauls for Mobile Networks}, journal = {Journal of Network and Computer Applications}, volume = {In Press}, year = {2010}, month = {04/2010}, pages = {--}, publisher = {Elsevier}, abstract = {Radio links are used to provide backhaul connectivity for base stations of mobile networks, in cases in which cable-based alternatives are not available and cannot be deployed in an economic or timely manner. While such wireless backhauls have been predominantly used in redundant tree and ring topologies in the past, mobile network operators have become increasingly interested in meshed topologies for carrier-grade wireless backhauls. However, wireless mesh backhauls are potentially more susceptible to security vulnerabilities, given that radio links are more exposed to tampering and given their higher system complexity.
This article extends prior security threat analyses of 3rd generation mobile network architectures for the case of wireless mesh backhauls. It presents a description of the security model for the considered architecture and provides a list of the basic assumptions, security objectives, assets to be protected and actors of the analysis. On this foundation, potential security threats are analyzed and discussed and then assessed for their corresponding risk. The result of this risk assessment is then used to define a set of security requirements. Finally, we give some recommendations for wireless mesh backhaul designs and implementations following these requirements.}, keywords = {Security analysis, Wireless mesh backhauls, Mobile networks}, author = {Frank A. Zdarksy, Sebastian Robitzsch, Albert Banchs} }
@inproceedings { 468, title = {A Case Study on Merging Strategies for Authoring QoE-based Adaptive Hypermedia}, booktitle = {ECTEL 2009}, year = {2009}, month = {09/2009}, abstract = {This paper describes recent work on strategy merger development in the authoring process of adaptive hypermedia. The goal of a merging strategy is to break a complex adaptation decision into a number of simpler ones which may be reused more easily and applied in different orders. To demonstrate the proposed method we present an example case study and sample strategies written in the LAG language. The case study is based on a recently proposed model for Quality of Experience in e-learning. This model exposes the complex interaction between a number of factors affecting QoE and hence presents a good candidate for the application of a strategy merger. Finally some evaluation points are identified, a conclusion is drawn and next steps are outlined.}, keywords = {LAG, Quality of Experience, Quality of Service, Multimedia Learning, Educational Adaptive Hypermedia, Adaptation, Strategy merger}, author = {Scotton, J. and Moebs, S, and McManis, J. and Cristea, A.I.} }
@inproceedings { 470, title = {QoE-MOT – A Learner Quality of Experience- Oriented Authoring Tool}, booktitle = {European Conference on Technology Enhanced Learning, A3H: 7th International Workshop on Authoring of Adaptive and Adaptable Hypermedia}, year = {2009}, month = {09/2009}, abstract = {This paper introduces Quality of Experience My Online Teacher (QoE-MOT), a user quality of experience oriented version of the generic authoring tool MOT. QoE-MOT is an authoring tool which enables the creation of performance-aware adaptive courses, by adapting the educational content to the learner network conditions. MOT was developed based on LAOS, a complex five layer authoring model. In similar fashion, QoE-MOT was constructed following the QoE-LAOS, a learner quality of experience oriented authoring model. This paper illustrates how an adaptive educational course has been enhanced with performance oriented metadata and how this metadata and QoE parameters are used during the adaptation process.}, keywords = {Authoring tool, Adaptive e-learning, LAOS, QoE, MOT, LAG}, author = {Andreea Molnar and Cristina Hava Muntean} }
@inproceedings { 469, title = {Billing Issues when Accessing Personalised Educational Content}, booktitle = {China-Ireland International Conference on Information and Communications Technologies (CIICT 2009)}, year = {2009}, month = {08/2009}, abstract = {The increased affordability of mobile devices combined with the availability of the latest wireless technologies have made mobile devices an attractive tool for learning. Nowadays learners can choose between multiple wireless networks with different characteristics, belonging to the same or to different mobile operators. Unfortunately, the Internet billing plans are still difficult to predict and control by most users. This paper presents an algorithm which aims to determine the best network, from a list of available ones (in terms of price), for delivering the selected educational content.}, keywords = {cost, mobile data billing plan, mobile learning, adaptive and personalised learning}, author = {Andreea Molnar and Cristina Hava Muntean} }
@inproceedings { 261, title = {Performance Aware and Cost Oriented Adaptive e-Learning Framework}, booktitle = {IADIS International Conference e-Learning}, year = {2009}, month = {06/2009}, abstract = {Nowadays learners have access to multiple wireless networks from the same hand held device challenging them to choose the best network in terms of cost and performance. However, the Internet billing plans are still difficult to understand, predict and control by most users. This paper presents a user oriented adaptive e-learning framework which takes into consideration: (i) the learner profile when content adaptation is done, (ii) user device that can have multiple wireless connections with different characteristics, (iii) how much the learner is willing to pay, and (iv) the network delivery performance. The goal is to ensure that the learner gets educational content that best suits his/her profile and that content will be delivered over the network which assures the best delivery performance, maintaining also a small price for getting the requested information.}, keywords = {adaptive and personalised e-learning, wireless connectivity, budget, framework, user modelling}, author = {Andreea Molnar and Cristina Hava Muntean} }
@inproceedings { 260, title = {Enhancing Domain Model with Performance Oriented Metadata for Adaptive E-learning Systems }, booktitle = {EdTech}, year = {2009}, month = {05/2009}, abstract = {Due to the increasing complexity of web site navigation, but also as a response to the “one size fits all” approach, adaptation mechanisms have emerged and have started to be used by a large number of on-line educational systems. As educational content may be delivered though various types of networks that differ in characteristics and vary with the time, the quality of the transmitted information is affected. PAMAH (Performance-Aware Multimedia-based Adaptive Hypermedia) proposes to overcome this barrier by taking into consideration in the personalisation process not only the classic learner profile but also the performance of the network connection used by the learner, when rich media content is delivered. This paper focuses on presenting performance oriented metadata required for modelling the educational content and for enhancing the adaptation process. The goal is to provide a personalised media rich content suitable for the learner network connection. }, keywords = {Adaptive and personalized e-learning, domain modelling, multimedia }, author = {Andreea Molnar and Cristina Hava Muntean} }
@inproceedings { 254, title = {Smooth Adaptive Soft Handover Algorithm for Multimedia Streaming over Wireless Networks}, booktitle = {IEEE Wireless Communications & Networking Conference (WCNC)}, year = {2009}, month = {04/2009}, abstract = {Inter-network mobility is achieved by allowing a mobile node to change its point of attachment to the network while preserving connectivity to its corresponding nodes. Most handover solutions proposed in the literature directly change the whole data flow from one network to another relying on only one network to transfer the entire data stream. These solutions involve a certain amount of quality degradation due to increasing loss and delay and suffer in terms of scalability, efficient resource allocation and resilience to different mobile node speeds. This paper proposes the Smooth Adaptive Soft-Handover Algorithm (SASHA) which increases the quality of the multimedia delivery process when performing handover in heterogeneous wireless environment by gracefully transferring the load from one connection to the other. }, keywords = {Heterogeneous mobile networks, Handover, Load balance, Multimedia streaming}, author = {Bogdan Ciubotaru and Gabriel–Miro Muntean} }
@inproceedings { 256, title = {A Novel Adaptive Multimedia Delivery Algorithm for Increasing User Quality of Experience during Wireless and Mobile E-learning}, booktitle = {IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB)}, year = {2009}, abstract = {Multimedia content is distributed via all types of networks to viewers found in a variety of locations and using different types of devices. Increasing the performance of multimedia stream delivery requires overcoming many technological challenges, all of them having a direct effect on the user perceived quality of experience. The quality of experience influences in turn the quality of any e-learning process. This is as users in general and learners in particular are becoming increasingly quality-aware in their expectations. Therefore delivering a good quality video stream as a part of any e-learning process is very important. This paper proposes a new adaptive multimedia delivery algorithm which can be used in the context of e-learning. The Dynamic Quality Oriented Adaptation Scheme (D-QOAS) adapts the multimedia content sent based on both user preferences and network conditions, while adjusting dynamically its adaptation policy during delivery. Simulation results show that for different user profiles and various network conditions the improvement in end-user perceived quality is significant. Important benefits are obtained in terms of the total number of simultaneous users and in the link utilization, as well as in quality as measured by some video quality metrics.}, keywords = {dynamic content adaptation, e-learning, multimedia, rate control, wireless networks}, author = {Vasile Horia Muntean and Gabriel-Miro Muntean} }
@inproceedings { 449, title = {Analysis of Real-Time Multimedia Transmission over PR-SCTP with Failover Detection Delay & Reliablity Level Diffrential}, booktitle = {IEEE International Conference on Communication Software & Networks}, year = {2009}, abstract = {The growing availability of different wireless access technologies provides the opportunity for real-time distribution of multimedia content using multi-homing technology. Investigating the behaviors and quality of such applications under heavy network load is necessary. This paper studies the effect of path failure detection threshold and reliability level on Stream Control Transmission Protocol Partial Reliability Extension (PR-SCTP) performance in symmetric and asymmetric path conditions respectively with different path loss rates. The platform Evalvid-SCTP implemented in the University of Delaware’s SCTP ns-2 module performs the emulation experiment.}, keywords = {Real-time; PR-SCTP; Evalvid-SCTP}, author = {C.Xu and E.Fallon and Y.Qiao and Gabriel-Miro Muntean and X.Li and A.Hanley} }
@proceedings { 229, title = {Analysis of Transparent Mode IEEE 802.16j System Performance with varying Numbers of Relays and Associated Transmit Power}, year = {2009}, abstract = {In this paper, the system capacity of IEEE 802.16j systems operating in transparent mode is investigated under varying numbers of relays and associated transmit power. The study is based on an extended variant of an analytical model defined in previous work and used to determine the throughput gain that can be achieved under a max-min fairness constraint. The study finds that significant overall throughput gains can be achieved over 802.16e systems: 125% and 55% gain with and without spatial reuse, respectively. However, the overall throughput gain drops as the transmit power at the relays (RSs) decreases despite the fact that a greater number of concurrent transmissions can be achieved due to less interference among the RSs’ transmissions. Decreasing the transmit power at the RSs eventually leads to a significant reduction of the achievable throughput gain even though a large number of RSs are deployed in scenarios with or without spatial reuse.}, keywords = {IEEE 802.16j, performance gain, transparent}, author = {Vasken Genc and Sean Murphy and John Murphy} }
@proceedings { 407, title = {An Adaptive Optimized RTO Algorithm for Multi-Homed Wireless Environments}, year = {2009}, abstract = {As a transport layer protocol SCTP uses end to end metrics, such as Retransmission Time Out (RTO), to manage mobility handover. Our investigation illustrates that Wireless LAN (WLAN) mobility causes continuously increased Round Trip Times (RTT) resulting from 802.11 MAC retransmissions, regardless of the service specified by upper layers. We present scenarios where the current understanding of SCTP switchover aggressiveness is invalid; spurious failovers together with excessive RTO result in new forms of receiver buffer blocking communication failure. Given wireless mobility performance issues, together with the ambiguity of end to end metrics, we propose an Adaptive Optimized RTO algorithm for wireless Access Networks (AORAN) which uses local as well as end to end metrics to manage mobility. AORAN measures RTT between the mobile node and Access Point (AP) to calculate wireless and Internet RTO subcomponents. We also show binary exponential backoff has negative effects on SCTP with increased wireless RTT; AORAN introduces a decision mechanism which implements backoff on RTO subcomponents only when appropriate.}, keywords = {SCTP, mobility, multi-homing, failover, receiver buffer blocking}, author = {S.Fallon and P.Jacob and Y.Qiao and L.Murphy} }
@inproceedings { 343, title = {Bandwidth Allocation in DiffServ Enabled Ethernet Passive Optical Networks}, booktitle = {IET Communications}, year = {2009}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Ethernet Passive Optical Networks (EPONs) have attracted consider- able attention from industry as they offer a simple, highly flexible and cost effective solution to the problem of providing broadband access to a customer. In this paper, a new approach to bandwidth allocation in EPONs is presented where the Optical Line Terminator (OLT) has full control over the access mechanism. This results in much simpler Optical Network Unit (ONU) architecture. It is shown in this paper that such an OLT-centric architecture offers full support for Differentiated Services and makes enforcement of Service Level Agreements possible. Extensive simulation experiments show that bandwidth allocation algorithms deployed in such a central- ized environment can deliver good performance in terms of average and maximum packet delay. In this paper two new algorithms are introduced that target SLA- aware EPONs and provide a good protection of offered quality of service against interference from other sources.}, keywords = {Ethernet,LAN}, author = {Nowak,D. and Murphy,J. and Perry,P.} }
@proceedings { 472, title = {CLOPS: A DSL for Command Line Options}, year = {2009}, abstract = {Programmers often write custom parsers for the command line input of their programs. They do so, in part, because they believe that both their program’s parameterization and their option formats are simple. But as the program evolves, so does the parameterization and the available options. Gradually, option parsing, data structure complexity, and maintenance of related program documentation becomes unwieldy. This article introduces a novel DSL called CLOPS that lets a programmer specify command line options and their complex inter-dependencies in a declarative fashion. The DSL is supported by a tool that generates the following features to support command line option processing: (1) data structures to represent option values, (2) a command line parser that performs validity checks, and (3) command line documentation. We have exercised CLOPS by specifying the options of a small set of programs like ls, gzip, and svn which have complex command line interfaces. These examples are provided with the Open Source release of the CLOPS system.}, keywords = {CLOPS, comman line options}, author = {Mikoláš Janota and Fintan Fairmichael and Viliam Holub and Radu Grigore and Julien Charles and Dermot Cochran and Joseph Kiniry} }
@article { 456, title = {Distributed Storage-Assisted Data-Driven Overlay Network for P2P VoD Services}, journal = {IEEE Trans. on Broadcasting}, volume = {55}, year = {2009}, pages = {1-10}, publisher = {IEEE}, abstract = {Providing VCR-like operations in Peer-to-Peer (P2P) environments is a significant challenge. This paper proposes a distributed Storage-assisted Data-driven overlay Network (SDNet) to support P2P Video-on-Demand (VoD) services. It integrates two networks: a Data-driven Overlay Network (DONet) and a multi-way tree. DONet is enhanced and used for the routine video distribution based on the buffer overlapping mechanism and gossip protocol. A novel algorithm which uses a multi-way tree structure and extra pre-fetching buffers at the nodes is proposed to support efficient VoD operations. Videos are divided into uniform segments, pre-fetched and stored in a distributed manner along the tree topology. The cooperation between DONet-based video delivery and the tree-located multimedia components enable multimedia streaming interactive commands to be performed efficiently. This paper presents and discusses the structure of SDNet and the distributed storage scheme and details the cooperation procedure. Simulation-based testing results show how the proposed SDNet is an efficient interactive streaming solution in a P2P environment.}, keywords = {DONet, multi-way tree, P2P VoD, VCR-like.}, author = {C.Xu and Gabriel-Miro Muntean and E.Fallon and A.Hanley} }
@inproceedings { 462, title = {Dynamic Switching Between Adaptive FEC Protocols For Multi-Source Streaming}, year = {2009}, abstract = {Multi-source streaming is essential for the design of a large-scale P2P streaming architecture. In this paper, we focus on improving the dependability of multi-source video streaming as an alternative to the more prevalent point-to-point streaming. We have designed and implemented a dynamic FEC (D-FEC) protocol for multi-source video streaming. Our D-FEC protocol has the ability to dynamically switch between 4 different FEC techniques to adapt to varying network conditions. A comprehensive performance evaluation was performed with a full-scale system prototype that gives insights into the behavior of the different adaptive FEC schemes, and shows the feasibility of the concept of switching FEC schemes during a streaming session. Guidelines are given in order to best design a FEC protocol switching strategy taking into account the experienced loss rate, the loss burstiness, and the original video stream rate.}, keywords = {P2P,FEC,Multi-Source Streaming}, author = {C.Lamoriniere and A.Nafaa and L.Murphy} }
@inproceedings { 463, title = {Interference Aware Relay Station Location Planning for IEEE 802.16j Mobile Multi-Hop Relay Networks}, booktitle = {12th ACM International Conference on Modeling Analysis & Simulation of Wireless & Mobile Systems}, year = {2009}, abstract = {In this paper, an interference aware algorithm for multi-cell Relay Station (RS) location planning problem is proposed in order to investigate the capacity gains possible using transparent mode 802.16j. The study focuses on the problem of determining the best choice of locations for RS from a given set of candidate sites - Base Station (BS) and Subscriber Station (SS) locations are assumed given. The proposed algorithm evaluates each RS based on the channel conditions of the links between the RS and its surrounding Subscriber Stations(SS) and the throughput gain it could deliver, taking into account co-channel interference. The performance statistics were collected over a large amount of experiments with many different configurations, including Base Station(BS) antenna types, number of candidate RS sites, RS transmitting power, with/without spatial reuse, etc. The results can be divided into two sections. Firstly, the algorithm was tested for optimality and scalability and was shown to perform well compared to classical Integer Programming solution techniques. Secondly, the results generated by the algorithm when applied to different scenarios were analyzed. Results show that using spatial reuse could achieve a much higher throughput gain, 3-5 time, then without using spatial reuse, although sectorised BS antenna limits the separation of co-channel RSs in a sector. The results demonstrate the characteristics of the trade-off between number of RSs and throughput gain for different configurations.}, keywords = {IEEE 802.16j, Spatial Reuse, Network Planning, Relay Station Location Problem}, author = {Y.Yu and S.Murphy and L.Murphy} }
@proceedings { 467, title = {IEEE802.11k Enabled Adaptive Physical Carrier Sense Mechanism for Wireless Networks(K-APCS)}, year = {2009}, abstract = {The existence of hidden and exposed nodes can have a significantly negative impact on the performance of IEEE802.11 networks. Such nodes can increase the probability of collisions and limit the spatial reuse on the channel. The value of the Physical Carrier Sensing Threshold (PCST) is instrumental to the trade-off between the number of hidden and exposed nodes in a system. This paper presents a new adaptive physical carrier sensing mechanism for wireless networks. The K-APCS algorithm maximizes the aggregate system throughput by optimizing the balance between the spatial reuse and the collision rate of a system. It incorporates 802.11k radio resource measurements and a frame loss bound on each node to enable the on-line tuning of the PCST. Simulations were performed on five variants of carrier sensing mechanisms; results show that K-APCS achieves the maximum spatial reuse with a throughput gain of 28% and the minimum collision rate with a decrease of 0.01%.}, keywords = {Performance optimization, Algorithm design, Simulation}, author = {C.Thorpe and S.Murphy and L.Murphy} }
@inproceedings { 259, title = {Learning Styles or Not? A Classroom Experience}, booktitle = {EdTech 2009 - the Irish Educational Technology Users' Conference}, year = {2009}, abstract = {Secondary Teacher Assistant Researchers (STARs) is a program of Science Foundation Ireland (SFI) that supports research collaboration between secondary school teachers and SFI funded scientists and engineers. The main idea of the program is to disseminate new skills and knowledge to teachers, which can be passed on to their students, by providing them an opportunity to work in a research laboratory. The goal of the project “Social Media to Support Learning Styles of Secondary Students in the Junior Cycle” was to explore whether a blended learning setting consisting of online learning materials matching different learning styles in addition to a face-to-face class results in a significant impact on the learning results.}, keywords = {learning styles, blended learning, social media}, author = {Brid Kilbane and Sabine Moebs and Jennifer McManis} }
@proceedings { 476, title = {Measurements and Evaluations for an IEEE 802.11a Based Carrier-Grade Multi-radio Wireless Mesh Network Deployment}, year = {2009}, abstract = {Although there currently exists a number of Wireless Local Area Network based mesh network deployments most have been deployed to provide best effort broadband Internet access. Consequently, they cannot meet the requirements of network operators in order to utilise these networks to offer carrier grade services. The goal of providing carrier grade services over a wireless mesh infrastructure requires high performance in terms of throughput and reliability. One way of achieving this increase in performance is to utilise multi-radio Mesh Nodes, however, due to the Physical Layer layer limitations of 802.11a this can have significant problems. This paper analyses these issues and investigates what performance can be expected when frequency multiplexing is considered. The results presented in this paper are based on real measurements taken from multi-radio Mesh Nodes and are evaluated using statistical algorithms. The main contribution of this paper is an analysis of the impact of the Adjacent Channel Interference effect in 802.11a based multi-radio Mesh Nodes.}, keywords = {802.11a, Measurement, Multi- Radio, Wireless Mesh Network, Wireless LAN }, author = {Sebastian Robitzsch and Christian Niephaus and John Fitzpatrick and Mathias Kretschmer} }
@inbook { 232, title = {Network Planning for IEEE 802.16j Relay Networks}, booktitle = {WiMAX Network Planning and Optimization }, year = {2009}, publisher = {Auerbach Publications}, abstract = {In this chapter, a problem formulation for determining optimal node location for Base Stations (BSs) and Relay Stations (RSs) in relay-based 802.16 networks is developed. A number of techniques are proposed to solve the resulting Integer Programming (IP) problem - these are compared in terms of the time taken to find a solution and the quality of the solution obtained. Finally, there is some analysis of the impact of the ratio of Base Station (BS)/Relay Station (RS) costs on the solutions obtained. Three techniques are studied to solve the IP problem: (1) a standard branch and bound mechanism, (2) an approach in which state space reduction techniques are applied in advance of the branch and bound algorithm and (3) a clustering approach in which the problem is divided into a number of sub-problems which are solved separately, followed by a final overall optimisation step. These different approaches were used to solve the problem. The results show that the more basic approach can be used to solve problems for small metropolitan areas; the state space reduction technique reduces the time taken to ¯nd a solution by about 50%. Finally, the clustering approach can be used to find solutions of approximately equivalent quality in about 30% of the time required in the first case. After the scalability tests were performed, some rudimentary experiments were performed in which the ratio of BS/RS cost was varied. The initial results show that for the scenarios studied, reducing the RS costs results in more RSs in the solution, while also decreasing the power required to communicate from the mobile device to its closest infrastructure node (BS or RS).}, keywords = {relay planning}, author = {Yang Yu and Vasken Genc and Sean Murphy and Liam Murphy} editor = {Y. Zhang}, }
@article { 408, title = {Open Corpus Architecture for Personalised Ubiquitous e-Learning}, journal = {Personal & Ubiquitous Computing }, volume = {13}, year = {2009}, pages = {197-205}, publisher = {Springer London}, abstract = {As the e-learning area matures, there are a growing number of e-learning content providers that produce and distribute material that covers a large range of topics, differs in quality and is represented in various formats. Lately, different devices and various network technologies allow extensive user access to educational content almost anywhere, anytime and from any device. Ubiquitous e-learning has the potential to provide continuous and context-based, educational material to human learners anytime, anywhere and on any device. Since each person has different expectations related to the content, the performance of the delivery and display of that content, it is desirable for an ubiquitous e-learning environment to provide user-oriented personalisation of e-learning material. However very often there are multiple sources of e-learning material at various web locations (open corpus resources) that cover the same topic, but differ in terms of quality, formatting and even cost. It is very difficult for learners to select the content that best suits their interests and goals, characteristics of the device used and delivery network as well as their cost budget. This paper proposes an innovative ubiquitous e-learning environment called Performance-based E-learning Adaptive Cost-efficient Open Corpus frameworK (PEACOCK) that provides support for the selection and distribution of personalised e-learning rich media content (e.g. multimedia, pictures, graphics and text) to e-learners such as it will best suit users’ interests and goals, meet their formatting preferences and cost constraints, while considering the limitations introduced by the end-user devices and the delivery networks to the user. PEACOCK’s main goal is to maximise the users’ e-learning experience and increase their learning satisfaction and learning outcome. }, keywords = {Adaptive e-learning systems - User-oriented personalisation - Cost-efficiency - Ubiquitous e-learning environment }, author = {C.H.Muntean and Gabriel-Miro Muntean} }
@inproceedings { 342, title = {Optimising Metropolitan Area Wireless Path Selection using Media Independent Handover}, booktitle = {International Workshop on Cross Layer Design}, year = {2009}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The Stream Control Transmission Protocol (SCTP) is a transport layer protocol which can support mobility through its multi-homing feature. SCTP's mobility support can be subdivided into 2 areas: path performance evaluation and switch implementation. As a transport layer protocol, SCTP's path performance evaluation is limited by its end-to-end network view. In modern heterogeneous networks, it is likely that the wireless access element of an end-to-end association is the point of performance degradation. SCTP's adherence to protocol boundaries abstracts the precision and meaning of performance metrics. In this paper, we analyze how the emerging cross layer switch management approach, Media Independent Handover (MIH), can be used to optimize path selection for metropolitan area wireless broadband networks. In such an environment line of sight can easily be obstructed, causing temporary path communication failure. We investigate how Received Signal Strength (RSS) can be used as a performance indicator, which triggers MIH path migration events in such a scenario. Results are presented which illustrate that our MIH based approach has significant performance improvement over standard SCTP strategies.}, keywords = {cross layer, MIH, SCTP, mobility, WiMax}, author = {Fallon,E. and Murphy,L. and Murphy,J.} }
@article { 244, title = {Performance-aware Replication of Distributed Pre-recorded IPTV Content}, journal = {IEEE Transactions on Broadcasting Special Issue}, volume = {(in press)}, year = {2009}, pages = {-}, publisher = {IEEE}, abstract = {Video recording in IPTV systems is a promising service that provides time-shifted services in relation to storing TV content closer to user devices such as set-top boxes. Existing approaches do not support collaboration between nodes which have correlated contents, a fact that can affect the performance of the overall system. To make this service more interactive and proactive, this paper presents the architecture using the Smart Personal Information Network (Smart PIN) as a novel performance-based content sharing network for IPTV content which uses a user-centric utility-based Multimedia Data Replication Scheme (MDRS). This allows the exchange of data based on both network performance and user interest in exchanged multimedia content in order to achieve ef?cient content sharing. The proposed solution is evaluated through extensive simulations and results show much improved behaviour in comparison with two other existing general purpose data replicat on schemes.}, keywords = {IPTV, Data replication, Content management, Peer-to-peer}, author = {Seung-Bum Lee and Gabriel-Miro Muntean and Alan F. Smeaton} }
@inproceedings { 341, title = {Run-Time Correlation Engine for System Monitoring & Testing}, booktitle = {IEEE International Conference on Autonomic Computing(ICAC-09)}, year = {2009}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Today’s enterprise applications can produce vast amounts of information both during system testing and in production. Correlation of this information can be difficult as it is generally stored in a range of different event logs, the format of which can be application or vendor specific. Furthermore these large logs can be physically distributed across a number of different locations. As a result it can be difficult to form a coherent understanding of the overall system behaviour. This has implications for a number of domains (e.g. autonomic computing, system testers), where an understanding of the system behaviour at run-time is required (e.g. for problem determination, autonomic management etc.) This paper presents an approach and implementation of run-time correlation of large volumes of log data and symptom matching of known issues in the context of large enterprise applications. Our solution provides for automatic data collection, data normalisation into a common format, run-time correlation and analysis of the data to give a coherent view of system behaviour at run-time and a symptom matching mechanism that can identify known errors in the correlated data on the fly.}, keywords = {System Monitoring and Testing, Event Correlation, Event Filtering}, author = {Holub,V. and Parsons,T. and O'Sullivan,P. and Murphy,J.} }
@article { 253, title = {SASHA - A Quality-Oriented Handover Algorithm for Multimedia Content Delivery to Mobile Users}, journal = {IEEE Transactions on Broadcasting Special Issue}, volume = {(in press)}, year = {2009}, pages = {-}, publisher = {IEEE}, abstract = {The convergence of the existing network access technologies to a common IP-based architecture and the increase in popularity of accessing video content over the Internet makes IPTV a promising solution for media and entertainment industries. Additionally, video content delivery to the increasingly popular mobile devices over heterogeneous wireless networks makes IPTV even more appealing. However the distribution of multimedia content over heterogeneous wireless networks to mobile devices involves significant technical challenges related to mobility management and quality of service provisioning. The existing solutions do not consider quality of service as a decision making parameter for mobility management in general and handover management in particular. This paper proposes the Smooth Adaptive Soft Handover Algorithm (SASHA), a novel quality-aware approach to handover based on load balancing among different networks using a comprehensive, Quality of Multimedia Streaming (QMS), function for decision making. SASHA represents the handover management solution at the core of the more comprehensive Multimedia Mobility Management System (M3S), a quality oriented mobility management framework for multimedia applications which maximizes user perceived quality by efficiently exploiting all available communication resources. Simulation-based testing results are presented, outlining the performance of SASHA in different mobility scenarios. The evaluation is performed for different number of nodes performing handover simultaneous and for various situations in terms of networks’ overlapping area. The results shown indicate how SASHA outperforms other three mobility management solutions in terms of quality, scalability and resilience to the dynamics of the networks’ overlapping area. }, keywords = {Multimedia streaming, IPTV, Heterogeneous networks, Mobility, Handover}, author = {Bogdan Ciubotaru and Gabriel-Miro Muntean} }
@article { 475, title = {Supporting carrier grade services over wireless mesh networks: The approach of the European FP-7 STREP CARMEN [Very Large Projects]}, journal = {IEEE Communications Magazine}, volume = {47}, year = {2009}, pages = {14-16}, publisher = {IEEE}, abstract = {CARMEN is a three-year Specific Targeted Research Project (STREP) funded by the European Commission within the 7th Framework Program. The CARMEN access network will complement existing access technologies by exploiting low cost mesh networking techniques, thus minimizing deployment and maintenance costs. The CARMEN architecture introduces an abstraction layer that hides the specifics of the underlying access technology providing an abstract interface on top of which higher layers can be easily developed. This allows for the integration of current and future heterogeneous wireless technologies to provide scalable and efficient mobile ubiquitous Internet access, able to adapt to different environments and user requirements. Following these goals, CARMEN aims to define, study and implement link and technology abstractions, mobility support, and quality of service. The architecture also includes advanced monitoring features that allow for dynamic self-configuration, thereby reducing the installation and operational costs.}, keywords = {CARMEN, Specific Targeted Research Project, carrier grade services, metropolitan areas, wireless mesh networks }, author = {Arturo Azcorra and Thomas Banniza and David Chieng and John Fitzpatrick and Dirk von-Hugo and Marek Natkaniec and Sebastian Robitzsch and Frank Zdarsky} }
@inproceedings { 340, title = {System-Level Performance Evaluation of Multi-Cell Transparent Mode Relay 802.16j Systems}, booktitle = {IEEE Globecom 2009}, year = {2009}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In this paper, the system capacity of a multi-cell IEEE 802.16j system operating in transparent mode is investigated. A previous published analytical model is used and incorporates interference from neighbouring cells. The model can be used to determine downlink performance under max-min fairness constraints for both sectored and omnidirectional systems with different amounts of relays. The study provides guidelines on the design of 802.16j systems operating in transparent mode – specifically, how to maximise throughput for such systems. It is shown that inter-cell interference from relays is limited in a suburban environment and that relays can deliver significant gains over single hop systems: gains of 30% and 60% can be achieved without and with spatial reuse in an omnidirectional system while 15% and 25% in a sectorised system.}, keywords = {IEEE 802.16j, transparent relay, multicell, interference, spatial reuse, performance}, author = {Genc,V. and Murphy,S. and Murphy,J.} }
@inproceedings { 460, title = {Seamless Handover of IPTV Streams in a Wireless LAN Network}, year = {2009}, abstract = {A robust mechanism to enable seamless handover of streamed IPTV in a WLAN is presented. Handover in a wireless network is usually based on signal strength measurements, but that approach does not consider levels of congestion within the network. Here, the case of stationary nodes with varying levels of network congestion is considered. A scheme that analyses the jitter is used to establish the relationship between congestion and loss in WLANs. This Moving Average of Negative Jitter is used as the basis of a handover scheme which can minimize loss. The handover scheme uses a client with two simultaneous connections to the same server through two separate WLANs, and it is shown that the client can compare the jitter in the two streams to determine which network delivers the best performance; this information is then used to determine when to perform a handover. The proposed scheme is implemented and results are presented that show the successful handover of an RTP over UDP stream in a live WLAN environment. The test scenario used is aimed at “Over-The-Top” service delivery, but the core algorithm is expected to be more broadly applicable.}, keywords = {IPTV, Handover, Streamed Video, Wireless LAN1.}, author = {G.Cunningham and P.Perry and J.Murphy and L.Murphy} }
@article { 339, title = {Transmission Scheduling for Multihomed Transport Protocols with Network Failure Tolerance}, journal = {Telecommunication Systems Journal}, volume = {40}, year = {2009}, pages = {10 pages}, publisher = {Springer Netherlands}, abstract = {In heterogeneous network environments, the network connections of a multi-homed device may have significant bandwidth differential. For a multihomed transmission protocol designed for network failure tolerance, such as SCTP, path selection algorithms for data transmission drastically affect performance. This article studies the effect of path bandwidth differential on the performance of retransmission strategies in multi-homing environments. It identifies that fast retransmission on an alternate path may cause receive buffer blocking when path bandwidth differential is significant and the receive buffer is limited. A theoretical model is proposed for selecting retransmission path during the fast retransmission phase, based on receive buffer and path conditions. From these observations and analysis results, this article proposes that path selection strategies for transmitting new data and retransmitted data should be decoupled. A new path selection scheme is proposed and evaluated through SCTP simulations.}, keywords = {Multi-homing, Transmission Protocol, SCTP}, author = {Qiao,Y. and Fallon,E. and Murphy,L. and Murphy,J. and Hanley,A. and Shi,Z.} }
@article { 338, title = {Using Cross-Layer Metrics to Improve the Performance of End-to-End Handover Mechanisms}, journal = {Computer Communication Preprint Online}, volume = {10.1016}, year = {2009}, pages = {13 Pages}, publisher = {Elsevier}, abstract = {Network centric handover solutions for all IP wireless networks usually require modifications to network infrastructure which can stifle any potential rollout. This has led researchers to begin looking at alterna- tive approaches. Endpoint centric handover solutions do not require network infrastructure modification, thereby alleviating a large barrier to deployment. Current endpoint centric solutions capable of meeting the delay requirements of Voice over Internet Protocol (VoIP) fail to consider the Quality of Service (QoS) that will be achieved after handoff. The main contribution of this paper is to demonstrate that QoS aware handover mechanisms which do not require network support are possible. This work proposes a Stream Control Transmission Protocol (SCTP) based handover solution for VoIP called Endpoint Centric Handover (ECHO). ECHO incorporates cross-layer metrics and the ITU-T E-Model for voice quality assessment to accurately estimate the QoS of candidate handover networks, thus facilitating a more intelligent handoff decision. An experimental testbed was developed to analyse the performance of the ECHO scheme. Results are presented showing both the accuracy of ECHO at estimating the QoS and that the addition of the QoS capabilities significantly improves the handover decisions that are made.}, keywords = {Echo,SCTP,VoIP,E-Model,Sigma}, author = {Fitzpatrick,J. and Murphy,S. and Atiauzzaman,M. and Murphy,J.} }
@inproceedings { 461, title = {Using 802.11 MAC Retransmission for Path Selection in Multi-Homed Transport Layer Protocols}, booktitle = {IEEE Globecom}, year = {2009}, abstract = {The Stream Transmission Control Protocol(SCTP)is a transport layer protocol which can support mobility through its multi-homing feature. One of the key parameters used by SCTP to manage path selection is Retransmission Time Out(RTO).We illustrate that SCTP evaluation of underlying paths using end to end metrics,results is the calculation of excessive RTO for degraded wireless paths.}, keywords = {SCTP,RTO,MAC Retransmissions,Mobility}, author = {S.Fallon and P.Jacob and Y.Qiao and A.Hanley and L.Murphy} }
@proceedings { 237, title = {An Adaptive Vehicle Route Management Solution Enabled by Wireless Vehicular Networks}, year = {2008}, month = {21/09/2008}, abstract = {In order to accommodate the constantly growing number of vehicles on the road with which infrastructure provision is failing to cope, new means of optimizing the available road space are required. This paper presents a novel adaptive vehicle routing algorithm for TraffCon - an innovative Traffic Management System enabled by wireless vehicular networks. The algorithm combats the vehicular traffic congestion problem by seeking to optimize the usage of existing road capacity, while also minimising vehicle fuel consumption and emissions. Results demonstrate that the algorithm significantly increases road utilisation, reduces congestion, average journey times and fuel consumption in comparison with existing approaches.}, keywords = {Wireless networking, Vehicular Communication, Road Traffic Congestion}, author = {Kevin Collins, Gabriel-Miro Muntean} }
@proceedings { 236, title = {Route-based Vehicular Traffic Management for Wireless Access in Vehicular Environments}, year = {2008}, month = {21/09/2008}, address = {Calgary, Canada}, abstract = {Traffic congestion is a very serious problem which is becoming ever worse as the growth in the number of cars on the road significantly out-paces the provision of road capacity. This paper presents a novel vehicle routing algorithm for TraffCon - an innovative Traffic Management System for wireless vehicular networks - and discusses its complexity. The algorithm combats the traffic congestion problem by seeking to optimize the usage of the existing road capacity, reduce vehicle trip times and decrease fuel consumption and the consequent gas emissions. Results demonstrate that the algorithm significantly increases road capacity utilisation and consequently reduces traffic congestion in comparison with an existing approach.}, keywords = {Wireless networking, Vehicular Communication, Road Traffic Congestion}, author = {Kevin Collins, Gabriel-Miro Muntean} }
@proceedings { 247, title = {Analysis of Random Data Hopping in Distributed Multihop Wireless Networks}, year = {2008}, month = {18 November}, publisher = {IEEE}, address = {Hyderabad, India}, abstract = {Spatial reuse TDMA (time division multiple access) in multihop ad hoc network is a subject of intense research interest for next generation wireless systems. In this paper, the selection of concurrent communication pairs, that utilize the same resources, is formulated as a non-linear mixed integer programming problem. However, it has been found that the solution to this non-linear programming problem is NP-hard. Recently, a random data hopping (RDH) technique applied over a time slot partitioned system has been proposed by the authors as a novel heuristic algorithm. This random data hopping scheme is further studied in this paper for different values of traffic loads, and its performance is evaluated under realistic propagation conditions. It has been found that the variation of the system throughput with the traffic load follows a concave function, and it reaches its peak when the traffic load is around 30%.}, keywords = {Spatial reuse TDMA, interference avoidance model, random data hopping.}, author = {Hrishikesh Venkataraman and Gabriel-Miro Muntean} }
@proceedings { 235, title = {A Vehicle Route Management Solution for Wireless Vehicular Networks}, year = {2008}, month = {14/04/2008}, address = {Phoenix, AZ, USA}, abstract = {Traffic Congestion is a very serious problem which is growing worse as the number of cars on the road continues to increase, out-pacing the provision of road capacity. This paper presents a novel vehicle routing algorithm for TraffCon - an innovative Traffic Management System for Wireless Vehicular Networks. The algorithm tackles the traffic congestion problem by seeking to optimize the usage of the existing road capacity, reduce vehicle trip times and decrease fuel consumption and the consequent gas emissions. Results demonstrate that the algorithm significantly reduces congestion, journey times and fuel consumption and emissions in comparison with an existing approach.}, keywords = {Wireless networking, Vehicular Communication, Road Traffic Congestion}, author = {Kevin Collins, Gabriel-Miro Muntean} }
@article { 220, title = {Analysis of a Large-Scale VOD Architecture for Broadband Operators: A P2P-Based Solution}, journal = {IEEE Communications Magazine}, volume = {46}, year = {2008}, month = {12/2008}, pages = {47-55}, publisher = {IEEE}, abstract = {VOD services distribution is gaining unprecedented interest from the consumer communication industry due to its growing success in both the Internet and residential broadband market. In this article we present a scalable VOD distribution architecture for broadband operators. The solution is based on a P2P streaming concept in which a VOD streaming session requested by a given STB (Set-Top-Box) is actually provisioned via a multisource streaming session. This solution has the advantage of scaling naturally with the number of STBs in the network. In this article we focus on efficiently translating the popularity distribution into content availability in the network. Different aspects related to this issue are analyzed and challenges highlighted. }, keywords = {video on demand, peer-to-peer, popularity distribution, content availability}, author = {A. Nafaa and S. Murphy and L. Murphy} }
@inproceedings { 183, title = {A Learner, is a Learner, is a User, is a Customer - QoS-based Experience-aware Adaptation}, booktitle = {ACM Multimedia}, year = {2008}, month = {10/2008}, abstract = {This paper describes an outline of the doctoral thesis work concerning adaptation policies towards quality of experience (QoE) in performance-aware adaptive multimedia e-learning systems. QoE is considered to be mainly affected by the psychological concept of flow and learning-related factors. In turn, for multimedia systems, these factors can be heavily influenced by quality of service (QoS). In an ideal world, QoS would not be an issue and content optimally tailored to a user’s needs could always be perfectly delivered. Unfortunately, delivery conditions are not always ideal, and it may be infeasible to deliver certain multimedia content such as high quality video while maintaining an acceptable QoS. The goal of this research is to balance the constraints imposed by QoS restrictions with the requirements of flow and learning in order to produce the highest possible QoE for the learner using an adaptive multimedia system.}, keywords = {Algorithms, Performance, Design, Human Factors, QoE, QoS, Flow, Learning}, author = {Sabine Moebs} }
@inproceedings { 162, title = {Analysis of Variation in IEEE802.11k Channel Load Measurements for Neighbouring WLAN Systems}, booktitle = {ICT Mobile Summit}, year = {2008}, month = {06/2008}, publisher = {IEEE}, organization = {IEEE}, abstract = {This paper focuses on analysing the variation in IEEE802.11k channel load measurements for neighbouring WLAN systems. The channel load functionality was implemented in the QualNet simulation tool, and several scenarios were configured for testing. The effects of different numbers of active systems with different traffic patterns were examined. The results obtained indicate significant variation in channel load values calculated by different stations experiencing different levels of interference. This variation leads us to question the usefulness of a single channel load measurement; hence considerable care must be taken when using and interpreting such measurements. }, keywords = {IEEE802.11k, Channel Load Measurements, Interference}, author = {C. Thorpe and S. Murphy and L. Murphy} }
@inproceedings { 223, title = {A Clustering Approach to Planning Base Station and Relay Station Locations in IEEE 802.16j Multi-hop Relay Networks}, booktitle = {Proc. IEEE International Conference on Communications (ICC 2008)}, year = {2008}, month = {05/2008}, abstract = {In this paper, a clustering approach to solve a network planning problem for 802.16j relay networks is considered. Our clustering approach consists of three basic steps: (1) divide the nodes into k distinct clusters, (2) solve the planning problem separately for each cluster, and (3) perform a final optimization to reduce issues arising at cluster boundaries. Simulation results show that our approach is more efficient than existing approaches: solutions of equivalent quality can be found in 40% of the time. Thus our technique can be used to solve larger problems with similar hardware, or similar size problems in less time.}, keywords = {network planning,802.16j,Wimax,relay network,clustering}, author = {Yang Yu and Sean Murphy and Liam Murphy} }
@inproceedings { 187, title = {User-centric Utility-based Data Replication in Heterogeneous Networks.}, booktitle = {IEEE International Conference on Communications, Workshop on Digital Television and Mobile Multimedia Broadcasting (ICC 2008)}, year = {2008}, month = {05/2008}, abstract = {Information overload and convergence of devices aggravate the difficulties of accessing data distributed among various user devices especially when this is performed by mobile users and over heterogeneous wireless networks. Existing data replication systems help increase the performance of the distributed data system, but they do not consider users different levels of interest in various pieces of data and neither heterogeneous wireless connectivity issues. This paper presents the Smart Personal Information Network (Smart PIN), a performance and cost-aware personal information network which uses a novel usercentric utility-based data replication scheme to exchange content automatically, based on both network performance and user interests. The proposed user-centric data replication scheme s evaluation, through simulation, shows improved results in comparison with existing solutions.}, keywords = { Data replication, Utility Function, Heterogeneous Network}, author = {Seung-Bum Lee and Gabriel-Miro Muntean and Alan F. Smeaton} }
@inproceedings { 186, title = {Smart PIN: Utility-based Replication and Delivery of Multimedia Content to Mobile Users in Wireless Networks.}, booktitle = {IEEE International Symposium on Broadband Multimedia Systems and Broadcasting 2008: Mobile and Handheld Systems for Entertainment on the Go}, year = {2008}, month = {04/2008}, abstract = {Next generation wireless networks rely on heterogeneous connectivity technologies to support various rich media services such as personal information storage, file sharing and multimedia streaming. Due to users mobility and dynamic characteristics of wireless networks, data availability in collaborating devices is a critical issue. In this context Smart PIN was proposed as a personal information network which focuses on performance of delivery and cost efficiency. Smart PIN uses a novel data replication scheme based on individual and overall system utility to best balance the requirements for static data and multimedia content delivery with variable device availability due to user mobility. Simulations show improved results in comparison with other general purpose data replication schemes in terms of data availability.}, keywords = {Content management, Non-real-time service, Interactive systems, Mobile systems, Portable and handheld devices}, author = {Seung-Bum Lee and Gabriel-Miro Muntean and Alan F. Smeaton} }
@article { 221, title = {Performance Analysis of Multi-homed Transport Protocols with Network Failure Tolerance}, journal = {IET Communications}, volume = {2}, year = {2008}, month = {02/2008}, pages = {336-345}, publisher = {IET}, abstract = {This paper studies the performance of multi-homed transport protocols tolerant of network failure. It evaluates the performance of different retransmission policies combined with path failure detection thresholds, infinite or finite receive buffers for various path bandwidths, delays and loss rate conditions through SCTP simulation. The results show that retransmission policies perform differently with different path failure detection threshold configurations. It identifies that retransmission of all data on an alternate path with the path failure detection threshold set to zero performs best in symmetric path conditions but its performance degrades acutely in asymmetric path conditions even when the alternate path delay is shorter than the primary path delay. It illustrates that retransmission of all data on the same path with the path failure detection threshold set to one or zero gives the most stable performance in all path configurations. }, keywords = {Fault-tolerant computing, transport protocols}, author = {Y. Qiao and E. Fallon and J. Murphy and L. Murphy and X. Zhu and G. Hayes and A. Matthews and A. Hanley} }
@article { 222, title = {Forward Error Correction Strategies for Media Streaming over Wireless Networks}, journal = {IEEE Communications Magazine}, volume = {46}, year = {2008}, month = {01/2008}, pages = {72-79}, publisher = {IEEE}, abstract = {The success of next-generation mobile communication systems depends on the ability of service providers to engineer new added-value multimedia-rich services, which impose stringent constraints on the underlying delivery/transport architecture. The reliability of real-time services is essential for the viability of any such service offering. The sporadic packet loss typical of wireless channels can be addressed using appropriate techniques such as the widely-used packet-level Forward Error Correction. In designing channel-aware media streaming applications, two interrelated and challenging issues should be tackled: accuracy of characterizing channel fluctuations and effectiveness of application-level adaptation. The first challenge requires thorough insight into channel fluctuations and their manifestations at the application level, while the second concerns the way those fluctuations are interpreted and dealt with by adaptive mechanisms such as FEC. In this article we review the major issues that arise when designing a reliable media streaming system for wireless networks. }, keywords = {Forward error correction, multimedia streaming, wireless channel conditions}, author = {A. Nafaa and T. Taleb and L. Murphy} }
@inproceedings { 224, title = {Planning Base Station and Relay Station Locations in IEEE 802.16j Multi-hop Relay Networks}, booktitle = {Proc. 2nd IEEE Broadband Wireless Access Workshop, colocated with IEEE CCNC 2008}, year = {2008}, month = {01/2008}, abstract = {In this paper, a problem formulation for determining optimal node location for Base Stations (BSs) and Relay Stations (RSs) in relay-based 802.16 networks is developed. The formulation results in an Integer Programming problem. A small modification to the original model is also considered in which the state space is reduced by limiting which nodes can be associated with which. Standard branch and bound techniques are used to solve the problem. The key findings of the paper are that standard techniques can be used to find solutions to problems of small metropolitan scale or for areas within a larger city.}, keywords = {network planning,802.16j,Wimax,relay network}, author = {Yang Yu and Sean Murphy and Liam Murphy} }
@article { 455, title = {Advanced Solutions for Quality-Oriented Multimedia Broadcasting}, journal = {IEEE Trans. on Broadcasting}, volume = {54}, year = {2008}, pages = {494-498}, publisher = {IEEE}, abstract = {Multimedia content is increasingly being delivered via different types of networks to viewers in a variety of locations and contexts using a variety of devices. The ubiquitous nature of multimedia services comes at a cost, however. The successful delivery of multimedia services will require overcoming numerous technological challenges many of which have a direct effect on the quality of the multimedia experience. For example, due to dynamically changing requirements and networking conditions, the delivery of multimedia content has traditionally adopted a best effort approach. However, this approach has often led to the end-user perceived quality of multimedia-based services being negatively affected. Yet the quality of multimedia content is a vital issue for the continued acceptance and proliferation of these services. Indeed, end-users are becoming increasingly quality-aware in their expectations of multimedia experience and demand an ever-widening spectrum of rich multimedia-based services.}, keywords = {Multimedia,Network}, author = {Gabriel-Miro Muntean and G.Ghinea and P.Frossard and M.Etoh and F.Speranza and H.R.Wu} }
@inproceedings { 109, title = {A Learner, is a Learner, is a User, is a Customer - So what exactly do you mean by Quality of Experience?}, booktitle = {Adaptive Hypermedia and Adaptive Web-based Systems}, year = {2008},
abstract = {An e-learner’s Quality of Experience (QoE) is informed by previous experiences as a learner, a user of computer/web-based systems, and a customer. This paper surveys different concepts for Quality of Experience (QoE) from different areas such as psychology, internet marketing, web engineering, systems and product development as well as philosophy of education. They are summarized into a proposal for a definition of Learner QoE in adaptive multimedia e-learning systems. A number of factors are identified that are likely to impact on QoE. We propose a <st1:place w:st="on">Delphi</st1:place> study to be used to provide an initial ranking of the importance of these factors. Additional user testing will be required to confirm the findings of this study.
},
keywords = {adaptive hypermedia, quality of experience, educational philosophy}, author = {Sabine Moebs and Jennifer McManis} }
@inproceedings { 184, title = {ADAPTIVE SOCIAL CONNECTEDNESS IN A MULTIMEDIA E-LEARNING ENVIRONMENT}, booktitle = {China-Ireland Conference on ICT (CIICT)}, year = {2008}, abstract = {Adaptive hypermedia systems are beneficial to e-learners in tailoring content to individual characteristics such as prior knowledge, learning preferences, etc. However, unlike popular non-adaptive learning management systems such as Moodle and Blackboard they do not support social connectedness by allowing communication with other learners. This can lead to feelings of isolation amongst learners and ultimately learner demotivation. Enabling communication has been shown to improve cohesion within a learner group and allows a tutor to monitor learner participation and intervene before learners become disengaged. This paper outlines a stand-alone component connect! for the selection of multimedia communication tools in adaptive e-learning systems to support social connectedness. In addition to the already proven benefits of supporting social interaction, attaching such a module to an adaptive hypermedia system allows us to introduce the novel feature of tailoring the communication method to the individual needs of the learner. We draw on research in the area of media ecology to assist us in making our decisions.}, keywords = {adaptive systems, social connectedness}, author = {S. Moebs and J. McManis} }
@inproceedings { 230, title = {An Interference-Aware Analytical Model for Performance Analysis of Transparent Mode 802.16j Systems}, booktitle = {Broadband Wireless Access Workshop co-located with GLOBECOM}, year = {2008}, abstract = {In this paper, an interference-aware analytical model of IEEE 802.16j systems operating in transparent mode is described. The model can be used to determine the throughput gain that can be achieved by 802.16j relay- based systems under a max-min fairness constraint in which the difference between the data rate delivered to all subscribers is minimized. Two variants of the model are considered – one in which there is no spatial reuse and one in which there is spatial reuse. The study finds that this variant of 802.16j system can deliver significant gains over traditional single-hop access systems: 40% in the case in which there is no spatial reuse and up to 80% when spatial reuse is realised.}, keywords = {IEEE 802.16j, optimisation problem, performance gain, transparent multihop relay}, author = {Vasken Genc and Sean Murphy and John Murphy} }
@inproceedings { 335, title = {An Analysis of the Performance of an MIH Based Switch Strategy for Heterogenous Network Mobility}, booktitle = {IEEE 17th IST Mobile & Wireless Communications Summit}, year = {2008}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The increasingly ubiquitous deployment of wireless networks has created significant opportunities for mobile application developers. The availability of highcapacity, low financial cost networks has the potential to enable mobile application developers to offer feature-rich end-user-oriented product offerings. Standardisation efforts such as Media Independent Handover (MIH) will support this trend by providing developers with a detailed view of the financial cost and performance capabilities of available wireless and mobile networks. Even with the increasingly pervasive deployment of Wireless LAN (WLAN), it is unlikely those mobile applications will exclusively utilise WLAN networks, as many are deployed without consideration of seamless network mobility. In the scenario where WLAN coverage gaps exist, it will be necessary to utilise mobile networks such as UMTS as a communication bridge. In such an environment, the mobility support provided by multi-homed protocols such as the Stream Control Transmission Protocol (SCTP) has significant potential. This paper investigates how MIH performance characteristics - in particular the Received Signal Strength (RSS) from a WLAN Access Point (AP) - can be used to optimise SCTP switch performance. Results indicate that in certain situations there is a performance problem with utilising a "retransmit on same path" approach to lost packet retransmission when the primary path is explicitly set, as would be the case with MIH. Careful configuration of the RSS threshold for switchover is shown to alleviate the problem.}, keywords = {SCTP, WLAN, Network Migration}, author = {Fallon,E. and Murphy,L. and Murphy,J.} }
@inproceedings { 446, title = {A Balanced Tree-based Strategy for Unstructured Media Distribution in P2P Networks}, booktitle = {IEEE International Conference on Communication}, year = {2008}, abstract = {Most research on P2P multimedia streaming assumes that users access video content sequentially and passively. Unlike P2P live streaming in which the peers start playback from the current point of streaming when they join the streaming session, in P2P video-on-demand streaming VCR-like operations such as forward, backward, and random-seek have to be supported. Providing this level of interactive streaming service in a P2P environment is a significant challenge. This paper proposes a Balanced Binary Tree-based strategy for Unstructured video-ondemand distribution in P2P networks (BBTU). BBTU assumes videos can be divided into several segments which can be fetched from different peers. BBTU involves two steps: 1) balance binary tree construction based on a prefetching algorithm in order to support interactivity; 2) unstructured video dissemination over network based on gossip protocol, which is the overlay for video distribution. Analysis and simulation show how BBTU is an efficient interactive streaming solution in P2P environment.}, keywords = {P2P video-on-demand; interactivity; balanced}, author = {C.Xu and Gabriel-Miro Muntean and E.Fallon and A.Hanley and F.Karayel} }
@proceedings { 404, title = {An Analysis of Alterations to the SCTP RTO Calculation Mechanism for WLAN Environments}, year = {2008}, address = {France}, abstract = {As a connection oriented transport layer protocol the Stream Control Transmission Protocol (SCTP) inherits many of the features of the Transmission Control Protocol (TCP) including the mechanism by which Retransmission Timeout (RTO) is calculated. Previous investigations have established that the mechanism through which SCTP calculates RTO is inappropriate in Wireless LAN (WLAN) environments. This paper investigates the performance implications of changes to the SCTP RTO calculation mechanism. In particular alterations to the parameters α, the smoothing factor, and β, the delay variance factor are investigated. Results indicate that performance improvements are achievable through careful selection of α and β values. Throughput improvements of 63% over the default mechanism defined in RFC 4960 are described. These performance improvements however, while significant, still can not address the switchover delays which result from the distortions caused by continuously increasing RTT values in WLAN environments.}, keywords = {SCTP,TCP,Wireless LAN}, author = {S.Fallon and P.Jacob and Y.Qiao and L.Murphy and E.Fallon and A.Hanley} }
@inproceedings { 448, title = {Comparitive Study of Real-Time Multimedia Transmission over Multi-Homing Transport Protocols}, booktitle = {IEEE /IFIP International Conference on Management of Multimedia Networks & Services}, year = {2008}, abstract = {The availability of multimedia applications suitable for deployment using 3G and GPRS networks has led to a requirement for end-to-end quality of service. More efficient mechanisms are needed in order to provide the required end user quality of service in wireless data networks. This paper investigates the performance implications of transmitting real-time multimedia content over a multi-homed transport protocol in a manner which is tolerant of network failure. It evaluates video quality with different retransmission policies combined with various path failure detection thresholds, path bandwidths, delays and loss rate conditions through Partial Reliable Stream Control Transmission Protocol (PRSCTP). A solution called Evalvid-SCTP, which is a trace driven simulation of MPEG-4 video over SCTP, was designed to achieve the performance evaluation.}, keywords = {PR-SCTP, Multi-homing, MPEG-4 Video, Congestion Control}, author = {C.Xu and Y.Qiao and E.Fallon and Gabriel-Miro Muntean} }
@article { 336, title = {Detecting Performance Antipatterns in Component Based Enterprise Systems}, journal = {Journal of Optical Technology}, volume = {7(3)}, year = {2008}, pages = {55-90(36 pages)}, publisher = {Bertrand Meyer}, abstract = {We introduce an approach for automatic detection of performance antipatterns. The approach is based on a number of advanced monitoring and analysis techniques. The advanced analysis is used to identify relationships and patterns in the monitored data. This information is subsequently used to reconstruct a design model of the underlying system, which is loaded into a rule engine in order to identify predefined antipatterns. We give results of applying this approach to identify a number of antipatterns in two JEE applications. Finally, this work also categorises JEE antipatterns into categories based on the data needed to detect them.}, keywords = {Component Systems,Antipatterns}, author = {Parsons,T. and Murphy,J.} }
@inproceedings { 332, title = {Development of an IEEE 802.11s Simulation Model for QualNet}, booktitle = {Networking & Electronic Commerce Research Conference}, year = {2008}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In this work, an initial variant of an 802.11s simulation model for the QualNet simulator is described. The tool builds on the existing QualNet 802.11 model by adding capabilities suitable for mesh networking. More specifically, the model provides support for propagation of beacon frames in mesh networks and link establishment procedures by which nodes attach to the network.}, keywords = {Networking,QOS}, author = {Alocci,I. and Murphy,S. and Nafaa,A. and Murphy,J.} }
@inproceedings { 447, title = {DONET-VOD:A Hybrid Overlay Solution for Efficient Peer-to-Peer Video on Demand Services}, booktitle = {IEEE International Conference on Multimedia & Expo(ICME)}, year = {2008}, abstract = {The existing DONet-based approach uses successfully a random gossip algorithm for scalable live video streaming. This pure mesh overlay network-based solution may lead to unacceptable latency or even failure of VCR operations in Video-on-Demand (VoD) services where nodes usually have different playing offsets, across a wide range. This paper proposes DONet-VoD which enhances DONet in order to address issues related to VoD delivery and VCR operations. In DONet-VoD, DONet principle is employed for the video distribution over the overlay network and a novel algorithm which uses a multi-way tree structure and extra prefetching buffers at the nodes is proposed to support efficient VoD operations. Video segments are prefetched and stored in a distributed manner in the nodes’ prefetching buffer along the tree. The cooperation between DONetbased video delivery and the tree-located multimedia components enable multimedia streaming interactive commands to be performed efficiently. This paper presents and discusses the prefetching scheme, details the cooperation procedure, and then analyses the performance of the proposed DONet-VoD}, keywords = {Peer-to-peer, VoD, prefetching, multiway}, author = {C.XU and Gabriel-Miro Muntean and E.Fallon and X.Li} }
@inproceedings { 218, title = {ECHO: A Quality of Service based Endpoint Centric Handover scheme for VoIP}, booktitle = {Wireless Communications and Networking Conference (WCNC)}, year = {2008}, abstract = {Existing terminal oriented handover mechanisms capable of meeting the strict delay bounds of real time applications such as VoIP do not consider the QoS of candidate handover networks. In this paper ECHO – a QoS based handover solution for VoIP– is proposed. ECHO is endpoint centric and does not require any network support; it leverages the SCTP transport protocol. ECHO incorporates network metrics that directly affect VoIP quality into the handover decision process. A dynamic variant of the ITU-T E-Model is used to calculate how the network metrics map to a user perceived voice quality metric known as the MOS. The MOS value is then used to make handover decisions between each of the available access networks. The results show that the addition of the QoS capabilities significantly improves the handover decisions that are made.}, keywords = {ECHO, QoS, E-Model, SCTP, Handover, VoIP}, author = {J. Fitzpatrick, S. Murphy, M. Atiquzzaman, J. Murphy} }
@inproceedings { 331, title = {Extracting Interactions in Component Based Systems}, booktitle = {IEEE Transactions on Software Engineering}, year = {2008}, publisher = {IEEE}, organization = {IEEE}, abstract = {Monitoring, analysing and understanding component based enterprise software systems are challenging tasks. These tasks are essential in solving and preventing performance and quality problems. Obtaining component level interactions which show the relationships between different software entities is a necessary prerequisite for such efforts. This paper focuses on component based Java applications, currently widely used by industry. They pose specific challenges while raising interesting opportunities for component level interaction extraction tools. We present a range of representative approaches for dynamically obtaining and using component interactions. For each approach we detail the needs it addresses, and the technical requirements for building an implementation of the approach. We also take a critical look at the different available implementations of the various techniques presented. We give performance and functional considerations and contrast them against each other by outlining their relative advantages and disadvantages. Based on this data, developers and system integrators can better understand the current state of the art and the implications of choosing or implementing different dynamic interaction extraction techniques.}, keywords = {Distributed objects, components, containers, tracing.}, author = {Parsons,T. and Mos,A. and Murphy,J. and Trofin,M. and Gschwind,T.} }
@article { 405, title = {Interference Mitigation in License-exempt 802.16 systems:a distributed approach}, journal = {Unlicensed Mobile Access Technology}, volume = {August }, year = {2008}, pages = {49-50}, publisher = {Auerbach Publications,Taylor & Francis Group}, abstract = {Operating in license-exempt IEEE 802.16 wireless spectrum is a challenging research issue. The research focus is on deriving intelligent algorithms to mitigate the interference that occurs between different users. In this chapter, we propose an enhancement to our previously published distributed approach to mitigate interference between 802.16 systems operating in close proximity, by introducing a re-listening mechanism to determine whether there are more subcarriers available in the channel than what the base stations (BSs) are currently using. Simulation results show that the re-listening mechanism offers a 100 percent throughput increase for some BSs. Our results also show the general trend of throughput variations between the downlink and the uplink, due to the differences in transmission power.}, keywords = {IEEE 802.16,}, author = {O.Ashagi and S.Murphy and L.Murphy} }
@article { 425, title = {Improving Learner Quality of Experience by Content Adaptation based on Network Conditions}, journal = {Computers in Human Behaviour}, volume = {24}, year = {2008}, pages = {1452-1472}, publisher = {Science Direct}, abstract = {Apart from user characteristics, properties of the network over which the content is delivered and device on which the content is displayed affect end-user perceived quality. This paper presents a learner quality of experience (QoE) model that apart from the user-related content adaptation, considers delivery performance-based content personalisation in order to improve user experience when interacting with an online learning system. A comparison-based study on the benefit of using the proposed learner QoE model in adaptive and personalized education was conducted involving the original AHA! and QoEAHA – a version of AHA! enhanced with the learner QoE model. Testing results demonstrate significant benefits in terms of learning achievement, learning performance, learner navigation and user QoE in favour of the learner QoE model-enhanced solution.}, keywords = {QoE}, author = {C.H.Muntean} }
@article { 228, title = {IEEE 802.16j Relay-based Wireless Access Networks: An Overview}, volume = {15}, year = {2008}, pages = {56-63}, publisher = {IEEE}, abstract = {Multihop wireless systems have the potential to offer improved coverage and capacity over single-hop radio access systems. Standards development organizations are considering how to incorporate such techniques into new standards. One such initiative is the IEEE 802.16j standardization activity, adding relay capabilities to IEEE 802.16 systems. This article provides an overview of this relay-based technology, focusing on some of the most pertinent aspects. In particular, the different modes of operation (transparent and non-transparent), framing structures, and network entry procedures are described. Some consideration of the issues in designing such systems is then given, which highlights when different features within the standard are most appropriate. As these systems are very new, many open issues remain to be resolved.}, keywords = {802.16j, overview, design}, author = {Vasken Genc and Sean Murphy and Yang Yu and John Murphy} }
@inproceedings { 193, title = {M3S - Multimedia Mobility Management and Load Balancing in Wireless Broadcast Networks}, booktitle = {China-Ireland International Conference on Information and Communications Technologies 2008 (CIICT 2008)}, year = {2008}, pages = {515-521}, abstract = {Wireless local-area networks represent a viable broadband Internet access solution for enterprise, residential and public areas. Due to its short range radio, multiple wireless access points are necessary to cover a certain physical area. The tendency of mobile users to group in certain areas of interest and of mobile devices to connect to the access point with the highest signal strength determines the overall network load to be highly unbalanced. To overcome this issues which drastically affects user bandwidth share as well as the efficiency of network resource utilization, special load balancing techniques has to be employed. This paper presents the Multimedia Mobility Management System (M3S), a quality oriented mobility management framework which aims at maximizing user perceived multimedia quality by efficiently distributing the traffic load over all the communication resources available. Simulation based testing results are presented, outlining the performance of M3S against other load balancing techniques which rely on mobile device re-association with least congested access points.}, keywords = {wireless broadcast networks, load balance, mobility management}, author = {Bogdan Ciubotaru and Gabriel-Miro Muntean} }
@inproceedings { 436, title = {M3S-Multimedia Mobility Management & Load Balancing in Wireless Broadcast Networks}, booktitle = {IET Chine-Ireland International Conference on Information & Communications Technology}, year = {2008}, abstract = {Wireless local-area networks represent a viable broadband Internet access solution for enterprise, residential and public areas. Due to its short range radio, multiple wireless access points are necessary to cover a certain physical area. The tendency of mobile users to group in certain areas of interest and of mobile devices to connect to the access point with the highest signal strength determines the overall network load to be highly unbalanced. To overcome this issues which drastically affects user bandwidth share as well as the efficiency of network resource utilization, special load balancing techniques has to be employed. This paper presents the multimedia mobility management system (M3S), a quality oriented mobility management framework which aims at maximizing user perceived multimedia quality by efficiently distributing the traffic load over all the communication resources available. Simulation based testing results are presented, outlining the performance of M3S against other load balancing techniques which rely on mobile device re-association with least congested access points}, keywords = {Multimedia,Wireless Networks,Mobile Communication}, author = {B.Ciubotaru and Gabriel-Miro Muntean} }
@article { 453, title = {Open Corpus Architecture for Personalised Ubiquitous e-Learning}, journal = {Personal & Ubiquitous Computing}, volume = {13}, year = {2008}, pages = {197-205}, publisher = {Springer Verlag}, abstract = {As the e-learning area matures, there are a growing number of e-learning content providers that produce and distribute material that covers a large range of topics, differs in quality and is represented in various formats. Lately, different devices and various network technologies allow extensive user access to educational content almost anywhere, anytime and from any device. Ubiquitous e-learning has the potential to provide continuous and context-based, educational material to human learners anytime, anywhere and on any device. Since each person has different expectations related to the content, the performance of the delivery and display of that content, it is desirable for an ubiquitous e-learning environment to provide user-oriented personalisation of e-learning material. However very often there are multiple sources of e-learning material at various web locations (open corpus resources) that cover the same topic, but differ in terms of quality, formatting and even cost. It is very difficult for learners to select the content that best suits their interests and goals, characteristics of the device used and delivery network as well as their cost budget. This paper proposes an innovative ubiquitous e-learning environment called Performance-based E-learning Adaptive Cost-efficient Open Corpus frameworK (PEACOCK) that provides support for the selection and distribution of personalised e-learning rich media content (e.g. multimedia, pictures, graphics and text) to e-learners such as it will best suit users’ interests and goals, meet their formatting preferences and cost constraints, while considering the limitations introduced by the end-user devices and the delivery networks to the user. PEACOCK’s main goal is to maximise the users’ e-learning experience and increase their learning satisfaction and learning outcome.}, keywords = {Adaptive e-learning systems �}, author = {C.H.Muntean and Gabriel-Miro Muntean} }
@inproceedings { 231, title = {Performance Analysis of Transparent Relays in 802.16j MMR Networks}, booktitle = {WiOpt}, year = {2008}, abstract = {A simulation study of the performance of transparent mode relay-based 802.16j systems is described. The study focuses on the gain in throughput that is possible in omnidirectional relay systems and increases in signalling requirements that arise due to the multihop network architecture. The study finds that the introduction of transparent mode relays cannot deliver improved throughput for a substantial part of the coverage area of a Base Station (BS) – only approximately half of the total area covered by the BS can benefit from throughput enhancement. Further, the study shows that 802.16j based systems require significant signalling overhead, with almost twice that of 802.16e in the cases studied. Finally, the study demonstrates that in a topology with users uniformly distributed within the BS cell coverage, the maximum throughput increase on the downlink that can be achieved is relatively low. Much further work is necessary to realise useful gains from these systems.}, keywords = {MMR, transparent multihop relay, performance, omnidirectional antenna}, author = {Vasken Genc and Sean Murphy and John Murphy} }
@inproceedings { 333, title = {Path Selection of SCTP Fast Retransmission in Multi-Homed Wireless Environments}, booktitle = {13th IFIP International Conference on Personal Wireless Communications}, year = {2008}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In heterogeneous wireless network environments, network connections of a device may have a significant differential. This paper studies the effect of path bandwidth differential on the performance of fast retransmission strategies in Multi-homing environments. It identifies that fast retransmission on an alternate path may cause receive buffer blocking when path bandwidth differential is significant and the receive buffer is limited. A theoretical model is proposed for selecting retransmission path during the fast retransmission phase, which is based on receive buffer and path conditions. The model is verified through simulations with various path differentials.}, keywords = {Wireless Communication}, author = {Qiao,Y. and Fallon,E. and Murphy,L. and Murphy,J. and Hanley,A.} }
@article { 454, title = {Region of Interest-based Adaptive Multimedia Streaming Scheme}, journal = {IEEE Trans. on Broadcasting}, volume = {54}, year = {2008}, pages = {296-303}, publisher = {IEEE}, abstract = {Adaptive multimedia streaming aims at adjusting the transmitted content based on the available bandwidth such as losses that often severely affect the end-user perceived quality are minimized and consequently the transmission quality increases. Current solutions affect equally the whole viewing area of the multimedia frames, despite research showing that there are regions on which the viewers are more interested in than on others. This paper presents a novel region of interest-based adaptive scheme (ROIAS) for multimedia streaming that when performing transmission-related quality adjustments, selectively affects the quality of those regions of the image the viewers are the least interested in. As the quality of the regions the viewers are the most interested in will not change (or will involve little change), the proposed scheme provides higher overall end-user perceived quality than any of the existing adaptive solutions.}, keywords = {Content adaptation, multimedia streaming,}, author = {Gabriel-Miro Muntean and G.Ghinea and T.N.Sheehan} }
@article { 334, title = {Static Verification of Component Composition in Contextual Composition Frameworks}, journal = {International Journal on Software Tools for Technology Transfers}, volume = {10(3)}, year = {2008}, pages = {247-261(15 pages)}, publisher = {Springer Berlin / Heidelberg}, abstract = {Contextual component frameworks, such as Enterprise JavaBeans (EJB), allow for components to specify boundary conditions for the runtime context. These conditions are satisfied at runtime by services of the underlying platform, thus ensuring that the context in which components run exhibits properties that allow them to operate correctly. Depending on how components call each other, it is possible that satisfying such conditions lead to problems such as reduced performance due to redundant service execution, or permanent errors (composition mismatches), due to incompatible boundary conditions. Currently, the semantics of these boundary conditions are expressed in natural language only, making it impossible to incorporate them into an automatic analysis tool. Furthermore, early understanding of how components call each other would be necessary, but it is currently difficult to achieve by means of a tool, as the method dispatch rules in a component system differ from the dispatch rules of the programming language(s) in which they were developed. We have developed a metamodel, $${\mathbb{M}}$$ , for describing boundary conditions, an analysis method, $${\mathbb{A}}$$ , and a static component-level call graph extraction method for EJB applications, CHA EJB . $${\mathbb{A}}$$ uses $${\mathbb{M}}$$ models to analyze inter-component call graphs, and thus detect problems such as composition mismatches or redundancies, thus allowing for remedial action to take place. We present $${\mathbb{M}},{\mathbb{A}}$$ and CHA EJB in this article, show that $${\mathbb{A}}$$ produces correct results, and describe a prototype analysis tool implementing the three, which we used to validate our approach on two popular EJB applications. }, keywords = {Software components - Contextual composition - Static analysis - Enterprise Java }, author = {Trofin,M. and Murphy,J.} }
@proceedings { 406, title = {SCTP Switchover Performance Issues in WLAN Environments}, year = {2008}, publisher = {Performance Engineering Lab}, address = {Las Vegas,Nevada}, abstract = {The increased number and diversity of underlying networks have made transparent network migration a necessity. Through its support for multi-homing the Stream Control Transmission Protocol (SCTP) enables seamless network mobility by abstracting multiple underlying physical paths into a single end-to-end association. One of these paths is selected as the primary. When a number of retransmission failures occur on the primary path, switchover is initiated to a secondary path. The number of retransmission attempts before switchover is initiated can be configured; however, the delay between each retransmission is managed internally in SCTP using a Retransmission TimeOut (RTO) value. This paper shows that the current SCTP mechanism for calculating RTO values is inappropriate in WLAN environments, since increased Round Trip Times (RTT) significantly distort RTO calculations. Experimental and simulated results indicate that SCTP behaves in a counterintuitive manner which allows more time for switchover as network conditions degrade: delays of up to 187 seconds can be experienced before switchover occurs. We show that additional SCTP parameters need to be carefully configured in order to reduce this switchover delay to a more acceptable level.}, keywords = {SCTP, WLAN, Switchover, Heterogeneous Networks}, author = {S.Fallon and P.Jacob and Y.Qiao and L.Murphy and E.Fallon and A.Hanley} }
@proceedings { 478, title = {Service quality improvement based on Network Attachment Subsystem extensions and Service Enhancement Function - Mesh Networks as an example}, year = {2008}, abstract = {...}, keywords = {WMN, Security}, author = {Andreas Roos and Sebastian Robitzsch and Bangnan Xu and Sabine Wieland and Andreas Schwarzbacher} }
@proceedings { 477, title = {Wireless Mesh Network Coverage with QoS Differentiation for Rural Areas}, year = {2008}, abstract = {...}, keywords = {WMN}, author = {Mathias Kretschmer and Sebastian Robitzsch and Christian Niephaus and Karl Jonas and Gheorghita Ghinea} }
@proceedings { 137, title = {TraffCon: An Intelligent Traffic Control System for Wireless Vehicular Networks}, year = {2007}, month = {28/08/2007}, address = {Dublin}, abstract = {Traffic Congestion is a very serious problem which is becoming ever worse as the growth in the number of cars on the road significantly outpaces the provision of road capacity. This paper presents TraffCon, a novel Traffic Management System (TMS) for Wireless Vehicular Networks that combats this problem by seeking to optimize the usage of the existing road capacity. It also outlines an architecture which includes a novel server-side decision making module, that enables the dissemination of instructions to vehicles; if followed these result in optimal road usage. }, keywords = {Wireless Networks,Traffic Management, Road Vehicles, Driver Instruction}, author = {Kevin Collins and Gabriel Miro Muntean} }
@inproceedings { 185, title = {Cost-oriented Context and Content Data Pair Delivery in Smart PIN}, booktitle = {China-Ireland International Conference on Information and Communications Technologies}, year = {2007}, month = {08 2007}, pages = {97-204}, abstract = {With evolutions of wireless technologies and advances in mobile services, ubiquitous devices have huge acquired and storing data which requires metadata for user to handle easily. For this purpose, this paper introduces Smart PIN - a novel performance and cost-oriented, context-aware personal information network. Smart PIN architecture includes network components, service components and management components. At the service components, there should be consideration for service discovery, service composition, data replication management and data pair transfer. Among these issues, this paper proposes a novel scheme for efficient delivery of context and content data based on pull and push scheme controlling logical and physical cost function.}, keywords = {Context-awareness, Data replication, Cost-effectiveness, Wireless PAN}, author = {Seung-Bum Lee and Gabriel-Miro Muntean and Alan F. Smeaton} }
@article { 403, title = {A Comparison Based Study of Quality Oriented Video on Demand}, journal = {IEEE Transactions on Broadcasting}, volume = {53}, year = {2007}, pages = {92-102}, publisher = {IEEE}, abstract = {The Quality Oriented Adaptation Scheme (QOAS) is used for high bit-rate multimedia streaming in local broadband multi-service all-IP networks. It balances two opposing goals: providing high quality multimedia-based services to end-users, and increasing the infrastructure utilisation and number of customers simultaneously served. Extensive objective testing results presented in this paper show that QOAS achieves high performance in terms of end-user perceived quality, loss rate, throughput, link utilisation, and number of customers simultaneously served. These results were obtained even in highly loaded and variable delivery conditions caused by traffic of different types, sizes, and variation patterns. QOAS performance was assessed stand-alone and in comparison with other existing solutions, adaptive and non-adaptive.}, keywords = {Adaptive video streaming, feedback control, grading scheme, end-user perceived quality.}, author = {G.Muntean and P.Perry and L.Murphy} }
@inproceedings { 233, title = {Adaptive H.264/MPEG-4 SVC video over IEEE 802.16 Broadband Wireless Networks}, booktitle = {Packet Video}, year = {2007}, abstract = {In this paper we present a solution for delivering streaming video-on-demand to subscribers via an 802.16 broadband wireless access network. The solution leverages the forthcoming H.264/AVC Scalable Video Coding (SVC) scheme and a mechanism to perform rate adaptation based on monitoring changes to the amount of flow traffic in the network at any time. A simulation-based approach is used to determine how the system performs in a rural deployment. Results show that the scheme provides high utilization of the wireless access system, at over 96%. Further, it maintains smooth transmission rate for the video applications, and ensures that no interruptions in continuous video playback occur during the streaming session. Lastly, a comparison with single-layer H.264/AVC is performed, showing how the proposed solution performs better with respect to both system utilization and the fact that no clients suffer interruptions in continuous playback.}, keywords = {IEEE 802.16, video streaming, scalable video coding}, author = {Odd Inge Hillestad and Andrew Perkis and Vasken Genc and Sean Murphy and John Murphy} }
@inproceedings { 323, title = {A Non-Elevated Scheduling Solution for First Person Shooter Games in IEEE 802.11 Networks}, booktitle = {IEEE Globecom 2007}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {First Person Shooter (FPS) games are a popular online gaming genre played predominately over wired networks. FPS games are highly interactive and have stringent delay requirements. However, the explosive growth in wireless LAN (WLAN) deployment has seen an increase in the use of such networks for gaming purposes. The varied performance of the IEEE 802.11 MAC Distributed Coordination Function (DCF) has tended to make WLANs unsuitable for FPS games. The IEEE 802.11e standard introduces Quality of Service (QoS) mechanisms including Enhanced Distributed Channel Access (EDCA) allowing prioritization of competing flows. Using the NS- 2 simulator, we evaluate the capability of 802.11g and 802.11e WLANs to support Quake IV games traffic in the presence of web traffic. We compare the results achieved using EDCA with those achieved by a non-elevated differentiated services scheduler known as Best Effort with Loss Trade-off (BELT). We find that the BELT scheduler compares favorably with EDCA in this context.}, keywords = {Online Gaming,LAN,QOS}, author = {Carrig,B. and Denieffe,D. and Murphy,J.} }
@inproceedings { 324, title = {A Congestion-only Charging Mechanism for Multiplayer Gaming in Diffrentiated Service Networks}, booktitle = {IEEE Globecom 2007}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In networks based on the Di®erentiated Services (Di®Serv) architecture, users may be presented the opportunity to choose their Assured Forwarding (AF) class. Users will attempt to maximize their Consumer Surplus (CS) in such an environment. They can increase their CS by choosing the lowest cost AF class that satis¯es their Quality of Service (QoS) requirements. Previously the authors have proposed an algorithm known as Consumer Surplus Maximization (CSM) [2]. Although this algorithm improves CS for users, widespread adoption of the algorithm can provoke network instability. If many users switch classes at once, degradation on one AF class can easily propagate. The likelihood of such an occurrence can be reduced by replacing ¯xed per- byte or per-packet charges associated with individual AF classes with a lightweight Congestion-only Charging (CoC) pricing mechanism. An additional charge is only applied to packets that receive discernible bene¯t from belonging to a particular class. We present simulation results from a networking scenario where users connect across a single Di®Serv domain to engage in a multiplayer First Person Shooter (FPS) game.}, keywords = {Pricing, Quality of Service, Di®Serv}, author = {Carrig,B. and Denieffe,D. and Murphy,J.} }
@inproceedings { 325, title = {An Application-quality based Mobility Management Scheme}, booktitle = {9th International Conference on Mobile & Wireless Communication Networks}, year = {2007}, publisher = {IEEE}, organization = {IEEE}, abstract = {Experimental results are presented for end-point controlled handover of a stream of voice-like packet data traffic between two independent wireless networks. The handover was achieved by using a version of the Stream Control Transmission Protocol (SCTP) that had been modified to monitor link quality and switch the primary connection to the “best” quality link available, where quality is evaluated in terms of application performance. The results clearly show that mobility management based solely on received signal strength is not suitable for wireless systems with contention-based access policies such as WiFi.}, keywords = {Mobile Communication, Network Testing, Packet Radio, Wide area networks, Wireless LAN, Handover, VoIP, Call Quality}, author = {Murphy,L. and Noonan,J. and Perry,P. and Murphy,J.} }
@inproceedings { 330, title = {A User Controlled Priority Selection Strategy for Multiplayer Games}, booktitle = {IEEE 4th Consumer Communications & Networking Conference}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Future Quality of Service (QoS) aware networks, such as those based on the Differentiated Services (DiffServ) architecture, will provide users with the opportunity to assign a priority to the traffic they receive and generate. Different priorities will entail different per-byte or per-packet charges. To aid users operating within such an environment, a priority selection strategy is required. In this paper, we propose a priority selection strategy based on the concept of Consumer Surplus (CS), which is the positive difference between utility or the user’s willingness-to-pay and cost. We then evaluate this strategy in a networking scenario where a user is involved in a multiplayer Counterstrike game, in which different priorities may be assigned to the downstream traffic. A utility curve, applicable to a First Person Shooter (FPS) game like Counterstrike, is presented. Using simulation results we show that for varied traffic loads, the CS strategy offers comparable application performance to that of always selecting the highest priority, but at a reduced cost to the user.}, keywords = {Qos,DiffServ,Online Gaming}, author = {Carrig,B. and Denieffe,D. and Murphy,J.} }
@inproceedings { 441, title = {A Mechanism for Greediness Management whenStreaming Multimedia to Portable Devices}, booktitle = {IEEE International Conference on Portable Information Devices}, year = {2007}, abstract = {The majority of streaming solutions use rate adaptaion based on congestion avoidance mechanisms that try to obtain as much bandwidth as possible from the limited network resources. This is good if we assume that all clients have equal requirements. However this is rarely the case as devices have unique characterstics ( e.g. screen size, screen resolution, location etc) that influence streaming related parameters & consequently the experience obtained by the end user.Due to the inherent greediness of streaming protocols & lack of knowledge about the characterstics of the users devices, this may result in certain devices receiving higher bandwidth share than they actually need & others not receiving enough,affecting the users perceived quality. Therefore there is a need to allow for client diffrentiation in order to provide an acceptable service for all cliemts,taking their device characterstics into account.This paper proposes a Greediness Control Algorithm(GCA),a specially designed application layer solution that tunes the greediness of the multimedia streaming based on client priority, to make more efficient use of the wireless network and increase the overall user perceived quality.}, keywords = {Algorithm,Multimedia,Portable Devices}, author = {E.Casey and Gabriel-Miro Muntean} }
@inproceedings { 443, title = {Adaptive Buffer Power Save Mechanism for Mobile Multimedia Streaming}, booktitle = {IEEE International Conference on Communication}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Wireless networks are becoming a part of everyday life for many people. When a mobile device has wireless LAN capability, multimedia content can be streamed over a wireless network to that device. However, a major disadvantage of all mobile devices is their limited battery lifetime. Multimedia streaming puts extra pressure on the battery, causing it to discharge faster. In some cases, streaming tasks cannot be completed purely because the battery of the device becomes fully discharged, which causes significant user dissatisfaction. Consequently, it is necessary to devise mechanisms to enable longer battery lifetime in order to support complex applications such as those involving mobile multimedia streaming. This paper proposes an Adaptive-Buffer Power Save mechanism (AB-PSM) for increasing the battery life of mobile devices during multimedia streaming. This increase is achieved by controlling how and when data is sent over a wireless LAN. AB-PSM introduces an additional buffer which hides data from the station it is intended for, allowing it to return to sleep and consequently saving power. Data is eventually delivered in one of the station’s following attempts to receive it. Tests involving AB-PSM have been performed and show good results in terms of significant increases in battery lifetime. The comparison between AB-PSM and the IEEE 802.11 legacy power save mechanism shows important increases in battery lifetime of more than 100%.}, keywords = {Wireless Network,Mobile Communications}, author = {J.Adams and Gabriel-Miro Muntean} }
@proceedings { 402, title = {A Distributed Approach to Interference Mitigation between OFDM-based 802.16 SystemsOperating in License-Exempt Mode}, year = {2007}, abstract = {An approach to mitigating interference between 802.16 license-exempt systems is proposed in this paper. More specifically, the approach focuses on solving problems which arise when two or more 802.16 systems operate on the same channel in close proximity to each other. The essence of the approach is a distributed mechanism which can apportion the available OFDM subcarriers between the different 802.16 systems. Simulation results show that the topology and the distributions of Base Stations (BSs) and the Subscriber Stations (SSs) have a significant impact on the system performance. Also, the system is very sensitive to the order in which the different nodes in the system are activated. Furthermore, the system with the given parameters can operate satisfactorily for up to 6 BSs in the same area, but scalability problems arise if more BSs are added.}, keywords = {802.16 Systems,OFDM}, author = {O.Ashagi and S.Murphy and L.Murphy} }
@inbook { 159, title = {Blended Learning: Towards a Mix for SMEs - Stakeholders and their Priorities}, booktitle = {Blended Learning}, year = {2007}, pages = {162-173}, publisher = {Prentice Hall, Singapore},
abstract = {
While blended learning seems to be quite suitable for small and medium sized enterprises (SMEs), current uptake of this learning method is low.
In this paper we propose a research design to examine the requirements for blended learning in SMEs. It is based on a three-round ranking-type Delphi
study. Participants for the panels were carefully selected. Our method takes into account that the area and the term of blended learning are discussed in very
different, partially contradicting connotations. For this purpose, we first provide the background of the initial research question and describe our research design.
Next, we present preliminary results of the Delphi study and the steps in preparation of round 2. Participants were selected for the online-Delphi and grouped into panels of SME learners, trainers and providers of e-learning as well as learners from large companies as a control group for the SME learners.
},
keywords = {blended learning, SME, learning technology, Delphi study, Requirements}, author = {Moebs, S. and Weibelzahl, S.} editor = {Fong, J. and Wang F.L.}, }
@inproceedings { 327, title = {Congestion-only Charging: A Novel PricinG Mechanism for use in Diffrentiated Service Networks}, booktitle = {ACM 4th International Conference on Heterogenous Networking for Quality,Reliablity,Security & Robustness,Qshine2007}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In networks based on the Di®erentiated Services (Di®Serv) architecture, users may be presented the opportunity to choose their Assured Forwarding (AF) class. Users will attempt to maximize their Consumer Surplus (CS) in such an environment. They can increase their CS by choosing the lowest cost AF class that satis¯es their Quality of Service (QoS) requirements. Previously the authors have proposed an algorithm known as Consumer Surplus Maximization (CSM) [2]. Although this algorithm improves CS for users, widespread adoption of the algorithm can provoke network instability. If many users switch classes at once, degradation on one AF class can easily propagate. The likelihood of such an occurrence can be reduced by replacing ¯xed per- byte or per-packet charges associated with individual AF classes with a lightweight Congestion-only Charging (CoC) pricing mechanism. An additional charge is only applied to packets that receive discernible bene¯t from belonging to a particular class. We present simulation results from a networking scenario where users connect across a single Di®Serv domain to engage in a multiplayer First Person Shooter (FPS) game.}, keywords = {Pricing, Quality of Service, DiffServ}, author = {Carrig,B. and Denieffe,D. and Murphy,J. and OSE,D.} }
@proceedings { 401, title = {Centralised Approaches to Subcarrier Allocation for OFDM-based 802.16 Systems Operating in License Exempt Mode}, year = {2007}, publisher = {Performance Engineering Lab}, abstract = {In this paper, three approaches to allocating resources between interfering IEEE 802.16 systems operating in license exempt mode are described. The schemes differ in terms of how they implement the fairness/utilisation trade-off. The three schemes are Throughput Maximisation (ThM), Maximum Fairness (MaF), and a Neighbour Based Resource Allocation (NBRA) approach which produces an approximately fair allocation, but makes more efficient use of any unallocated resources. The three schemes are compared in terms of their overall throughput and the fairness they can deliver. They are also compared with results obtained by a distributed algorithm we proposed in previous work. It is shown that the NBRA approach gives the best throughput/fairness trade-off. Also, the results show that the distributed approach significantly underperforms the full-knowledge resource allocation schemes described here.}, keywords = {IEEE 802.16,Throughput Maximisation(ThM),Maximum Fairness(MaF)}, author = {O.Ashagi and S.Murphy and L.Murphy} }
@inbook { 457, title = {Dynamic Handover in Wireless LAN/MAN Heterogenous Networks}, booktitle = {Mobile WiMAX:Towards Broadband Wireless Metropolitan Area Networks}, year = {2007}, publisher = {Auerbach Publications}, abstract = {In future generations of wireless networks, it is expected that different users with various multi-homed personal wireless devices will have the option of accessing their desired services via different available radio access networks. Given the variability of the radio environment properties and user mobility, the availability and characteristics of an access network will change in time and are highly dependent on location. As a result, dynamic reselection of the access network will be a necessary part of the mobility management mechanism (which maintains the session connectivity as the user moves and/or the available access characteristics change). In their selection of a radio access network customers will consider cost and perceptive quality preferences for the current application and will rely on intelligent network selection decision strategies to aid or automate their choice.}, keywords = {Wireless Network,Radio Network}, author = {O.Ormond and Gabriel-Miro Muntean} editor = {Y.Zhang and H.H.Chen}, }
@inproceedings { 322, title = {Dynamic Network Selection in Wireless LAN/MAN Heterogenous Networks}, booktitle = {Mobile WiMAX:Toward Broadband Wireless Metropolitan Area Networks}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In future generations of wireless networks, it is expected that different users with various multi-homed personal wireless devices will have the option of accessing their desired services via different available radio access networks. Given the variability of the radio environment properties and user mobility, the availability and characteristics of an access network will change in time and are highly dependent on location. As a result, dynamic reselection of the access network will be a necessary part of the mobility management mechanism (which maintains the session connectivity as the user moves and/or the available access characteristics change). In their selection of a radio access network customers will consider cost and perceptive quality preferences for the current application and will rely on intelligent network selection decision strategies to aid or automate their choice. These dynamic selection strategies will need to take into account different dynamic, and sometimes conflicting, metrics}, keywords = {Wireless Communication}, author = {Ormond,O. and Murphy,J. and Muntean,G.} }
@inproceedings { 329, title = {Deployment of Java Based Components in Embedded Environment}, booktitle = {International Conference Applied Computing}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Component-based development has brought the benefits of easier reuse, integration and rapid development into the software engineering process. Many contemporary component-based platforms (e.g. EJB, CCM, SOFA, Fractal) are implemented in Java because of Java features such as platform independence, dynamic loading, type safety, and others. Another reason is that Java becomes more and more ubiquitous as devices like mobile phones, PDAs, etc. embed the Java implementation. However in the area of embedded systems, applications are usually still monolithic and therefore hard to maintain and reuse. On the other hand, the embedded Java platform has several important limitations, which prevent straightforward reuse of component-based platforms. In this paper, we present how to overcome these limitations and use contemporary component platforms for developing applications for embedded systems. We demonstrate the approach on the SOFA 2.0 component platform. The paper shows that the only parts of the SOFA 2.0 platform, which have to be adapted, are the deployment process and the runtime environment. The rest of the platform suits for development for embedded systems without any change and allows for benefiting from SOFA 2.0 features like behavior validation, multiple communication styles, separated control part of components, etc.}, keywords = {Hierarchical components, deployment, embedded environment, Java.}, author = {Hnetynka,P. and Murphy,J.} }
@inbook { 458, title = {End User Quality of Experience Aware Personalised in E-Learning}, booktitle = {Architecture Solutions for E-Learning Systems}, year = {2007}, publisher = {IGI Global Publishing House}, abstract = {In the context of new devices and with a variety of network technologies that allow access to the Internet, the providers of e-learning materials have to ensure that the users have a positive experience using their e-learning systems and they are happy to re-use them. Adaptive Hypermedia research aims to provide personalised educational material that ensures a positive learning experience for the end-users. However, user experience is dependent not only on the content served to them, but also on the user perceived performance of the e-learning system. This leads to a new dimension of individual differences between Web users: the end-user Quality of Experience (QoE). We have proposed a solution for Adaptive Hypermedia Systems (AHS) that provides satisfactory end-user QoE through the use of a new QoE layer. This layer attempts to take into account multiple factors affecting QoE in relation to the delivery of a wide range of Web components such as text, images, video, audio. The effectiveness of our QoE layer has been tested in comparison to a standard educational AHS and the results of these tests are presented in this paper. Different educational-based evaluation techniques such as learner achievement analysis, learning performance assessment, usability survey and correlation analysis between individual student performance and judgment on system usability were applied in order to fully assess the performance of the proposed QoE layer. Results of the tests showed that the use of the QoE layer brought significant improvements in terms of user learning performance, system usability and user satisfaction with the personalised e-learning system while not affecting the user learning achievement }, keywords = {end-user QoE, adaptive hypermedia, e-learning, end-user perceived performance, learning performance }, author = {C.H.Muntean and Gabriel-Miro Muntean} editor = {C.Pahl}, }
@inproceedings { 217, title = {Evaluation of VoIP in a Mobile Environment using an SCTP based Handoff Mechanism}, booktitle = {IST Mobile Summit}, year = {2007}, abstract = {In parallel with the growth of VoIP services, a large number of manufacturers have begun to develop multimode devices capable of connecting to multiple wireless access networks simultaneously. These multimode terminals have, in principle, the capability to support seamless handover between different radio access networks. One handover solution that utilises the IP diversity which these multimode devices can deliver is SIGMA. SIGMA is a promising end-to-end transport layer handover solution based on SCTP. The objective of this paper is to investigate if SIGMA is capable of providing seamless handover of VoIP calls without degradation in voice quality. To achieve this, we developed a Linux based testbed on which we implemented a VoIP client and server using SIGMA handoff . Each voice call uses the G.711 voice codec over RTP. PR-SCTP is used in place of the traditional UDP as the transport layer protocol. SIGMA based handover was used during full duplex voice calls between the client and server. The ITU-T E-Model has been used to calculate the voice quality during the handover. Results show that SIGMA can be used as a seamless handover mechanism for VoIP without any impact on voice quality.}, keywords = {SCTP, VoIP, SIGMA, Seamless Handover}, author = {J. Fitzpatrick, S. Murphy, M. Atiquzzaman, J. Murphy} }
@inproceedings { 435, title = {Electronic Monitoring of Nutritional Components}, booktitle = {Information & Telecommunication Technology}, year = {2007}, abstract = {Obesity and other diseases related to unhealthy diet are problems of near epidemic proportion and become a growing issue every year. This paper presents a solution to this issue by proposing the use of a computer application that is able to suggest the appropriate products related to one’s diet, and to keep track of nutritional intake. The paper also describes the principle of the solution, system architecture and implementation and presents testing results. If the application’s instructions are followed by users it is expected that an optimal diet will be achieved resulting in users good health.}, keywords = {Healthy diet, e-health, utility function, nutrition control}, author = {Z.Fratczak and Gabriel-Miro Muntean and K.Collins} }
@inproceedings { 445, title = {Effect of Delivery Latency,Feedback Frequency & Network Load on Adaptive Multimedia Streaming}, booktitle = {IEEE 32nd Local Computer Neworks Conference }, year = {2007}, abstract = {As video on demand systems gain popularity, it seems likely that the desire to serve a high number of customers from limited network resources could lead to a degradation of the endusers’ perceived quality. Quality-Oriented Adaptation Scheme (QOAS) balances the need for high quality with increased network utilization when streaming multimedia. QOAS requires client-side monitoring of some transmission-related parameters, grading of the end-user’s quality and feedback that informs the server about the received quality. In response to this feedback, the server adjusts the streaming process in order to maximize the end-user perceived quality in the current conditions. This paper studies the effect of delivery latency and feedback frequency on quality-oriented adaptive multimedia streaming. It also shows how high end-user perceived quality is maintained in the presence of different types of background traffic while recording a significant increase in link utilization and a very low loss rate.}, keywords = {Adaptive video streaming, grading scheme, end-user}, author = {Gabriel-Miro Muntean} }
@inproceedings { 444, title = {Influence of Mobile User Velocity on Data Transfer in a Muti-Network Wireless Environments}, booktitle = {9th International Conference on Mobile & Wireless Communication Networks}, year = {2007}, abstract = {Heterogeneous wireless environments are now a reality in many urban areas. Designing and deploying a wireless network in such an environment is complicated by the unpredictable propagation paths of radio signals and by the unpredictable behaviour of the network users themselves. Network simulation and modelling can be used to assist in the design process. However, in order for simulation models to be effective they must be realistic. Efforts have been made to render simulation models more realistic through the analysis of real world wireless networks and through the examination and evaluation of existing simulation models. The most fundamental characteristics of a mobile user are their mobility, and the speed at which they move. The various velocities used in simulation models are unrealistic with respect to pedestrian behaviour in urban environments. In addition, the possible influence of mobile user velocity on the amount of data transferred by the user is not considered. In this paper we examine the influence of a mobile user’s velocity on throughput in a wireless network using a range of realistic velocities.}, keywords = {heterogeneous wireless network environment,}, author = {T.Casey and Gabriel-Miro Muntean and D.Denieffe} }
@inproceedings { 440, title = {Power Save Adaptation Algorithm for Multimedia Streaming to Mobile Devices}, booktitle = {IEEE International Conference on Portable Information Devices}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Batteries have not followed the exponential technological improvements of other mobile device related hardware, such as CPU, memory and wireless networking. Battery power often introduces significant limitations to the use of mobile devices and their applications, including those involved in multimedia streaming that have significant high power requirements. This paper proposes a power save adaptation algorithm for mobile multimedia streaming that aims to increase streaming time given limited battery power resources. The multimedia streaming process is divided into three stages: data reception, decoding and playing and power saving solutions for each of these stages are proposed. These power save mechanisms are then combined to give the power save algorithm. Preliminary tests results show that significant increases in battery lifetime have been achieved when the power save mechanisms proposed in this paper are used.}, keywords = {Algorithm,Multimedia Streaming,Mobile Devices}, author = {J.Adams and Gabriel-Miro Muntean} }
@article { 409, title = {Quality of Experience-LAOS:Create Once,Use Many,Use Anywhere}, journal = {International Journal of Learning Technology}, volume = {3}, year = {2007}, pages = {209-229}, publisher = {CG Publisher}, abstract = {This paper proposes QoE-LAOS, a Quality of Experience-oriented adaptive authoring model that enables performance-aware adaptation. It extends the existing LAOS authoring model in order to consider display and delivery performance issues. QoE-LAOS involves the addition of three new QoE sublayers: QoE Content Features sublayer, QoE Characteristics sublayer and QoE Rules sublayer. These proposed QoE sublayers are deployed at LAOS's Domain, Adaptation and Presentation Models, respectively. This paper formalises and exemplifies QoE-LAOS and discusses authoring-related issues in relation to each new sublayer. }, keywords = {adaptive hypermedia, adaptive educational hypermedia, AEH, adaptive author assistance, semi-automatic adding, authoring models, authoring tools, adaptive web application engineering, adaptive web application authoring, adaptive learning, adaptive systems,}, author = {C.H.Muntean and G.M.Muntean and J.McManis and A.I.Cristea} }
@inproceedings { 452, title = {Resource Efficient Quality-Oriented Wireless Broadcasting of Adaptive Multimedia Content}, booktitle = {IEEE Trans. on Broadcasting}, year = {2007}, abstract = {The performance of multimedia stream delivery is influenced by encoding scheme, streaming solution and network conditions. This paper studies the performance of multimedia streaming when using the Quality-Oriented Adaptive Scheme (QOAS) over an IEEE 802.11b Wireless LAN and compares it to that achieved when using other solutions that do not consider end-user quality in their delivery process such as TFRC, LDA+, and non-adaptive schemes. The performance is assessed in terms of average end-user perceived quality, number of concurrent streaming sessions, loss rate, delay, jitter and total throughput when streaming MPEG-4 encoded content. Simulation results show that the QOAS out-performs these other streaming solutions in all aspects of network delivery. QOAS can support a greater number of concurrent streaming sessions at a higher average quality. In addition, for the same number of clients QOAS achieved a higher average end-user quality, as well as better network delivery streaming performance parameters.}, keywords = {Adaptive multimedia streaming, end-user quality}, author = {Gabriel-Miro Muntean and N.Cranley} }
@proceedings { 398, title = {Reducing Runtime Complexity of Long Running Application Services via Dynamic Profiling & Dynamic Bytecode Adaption for Improved Quality of Service}, year = {2007}, publisher = {Performance Engineering Lab}, address = {Atlanta USA}, abstract = {We present a transparent optimisation framework for au- tomatically improving run-time performance of component- based enterprise applications. Run-time performance is im- proved by automatically identifying and dynamically switch- ing to an optimised but functionally equivalent program flow, for a specific transaction type. More precisely, one or more application components can have both static and dynamic inputs, where the former and its output remain mostly fixed from invocation-to-invocation, while the latter is unconstrained. Through dynamic profiling and run-time adaptation, an optimised program flow is derived, that al- lows only future execution of program points that operate on dynamic inputs and not static inputs. During execution, a target application is instrumented to switch to an opti- mised program flow. Additional instrumentation occurs to profile key program points that may invalidate an optimised program flow. If these points execute, then the application reverts back to its pre-optimised program flow. We evalu- ate and demonstrate how run-time performance for a typical thre-tired enterprise system can be improved for frequently accessed data that remains mostly static. For the applica- tion studied we showed a 49% marked improvement in the number of users serviced per second.}, keywords = {adaptation, Optimisation, Caching, Profiling, Object Caching, Java Language}, author = {J.Bergin and L.Murphy} }
@inproceedings { 326, title = {Supporting First Person Shooter Games in Wireless Local Area Networks}, booktitle = {IEEE 18th International Symposium on Personal,Indoor & Mobile Radio Communications}, year = {2007}, publisher = {IEEE}, organization = {IEEE}, abstract = {First Person Shooter (FPS) games are a popular online gaming genre played predominately over wired networks. FPS games are highly interactive and have stringent delay requirements. However, the explosive growth in wireless LAN (WLAN) deployment has seen an increase in the use of such networks for gaming purposes. The varied performance of the IEEE 802.11 MAC Distributed Coordination Function (DCF) has tended to make WLANs unsuitable for FPS games. The IEEE 802.11e standard introduces Quality of Service (QoS) mechanisms including Enhanced Distributed Channel Access (EDCA) allowing prioritization of competing flows. Using the NS-2 simulator, we evaluate the capability of 802.11g and 802.11e WLANs to support Quake IV games traffic in the presence of web traffic. We compare the results achieved using EDCA with those achieved by a non-elevated differentiated services scheduler known as Best Effort with Loss Trade-off (BELT). We find that the BELT scheduler compares favorably with EDCA in this context.}, keywords = {Online Gaming,LAN,QOS,IEEE 802.16}, author = {Carrig,B. and Denieffe,D. and Murphy,J.} }
@inproceedings { 328, title = {SCTP Performance Issue on Path Delay Diffrential }, booktitle = {WWIC 5th International Conference on Wired/Wireless Internet Communications}, year = {2007}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {This paper studies the effect of path delay on SCTP performance. It focuses on the SCTP fast retransmit algorithm and demonstrates that the performance in the current retransmission strategy will degrade acutely when the secondary path delay is less than the primary path delay at a certain level. The performance degradation is due to the disordered SACKs and constant congestion window size during the fast retransmit phase. Some modifications aimed at these problems are proposed and evaluated. This paper also identifies that the cause of the performance degradation in SCTP is a result of the single path configuration oriented design of the current fast retransmit algorithm. Several fast retransmission strategies are evaluated for different path delay and bandwidth configurations.}, keywords = {SCTP, Multi-homing, Retransmission strategy, Path difference.}, author = {Qiao,Y. and Fallon,E. and Murphy,L. and Murphy,J. and Hanley,A. and Zhu,X. and Matthews,A. and Conway,E.} }
@article { 399, title = {Towards Efficient Service-Level QoS Provisioning in Large Scale 802.11-Based Networks}, journal = {IEEE Network:Special Issue on Advances in Broadband Access Networks}, volume = {21}, year = {2007}, pages = {42-48}, publisher = {IEEE}, abstract = {Along with recent advances in mobile networking and portable computing technologies, there is a trend in the telecommunications industry toward the development of efficient ubiquitous systems that can provide a set of bandwidth-intensive and real-time services to multiple users while supporting their full mobility. Largescale deployment of 802.11-based technologies will play an integral part in the construction of such ubiquitous wireless mobile systems. A challenging task in the development of such networks is efficient provisioning of QoS-enabled services for mobile users. In this context, we propose a scheme that constantly monitors the overall network performance to perform admission control and traffic conditioning at the 802.11-based access points and mobile terminals. The focus is on servicelevel fairness, where different flows from the same traffic class can still receive the same QoS level even if they have different bit rates. Furthermore, given the mobility of users, the success of any resource allocation and admission control model depends on the continuity of QoS guarantees across different WLANs. This article proposes a dynamic service level agreement negotiation protocol that allows mobile terminals to perform handoffs between different WLANs while maintaining the agreed level of service. End users also can change their service levels in response to changes in network conditions.}, keywords = {Internet,802.11,Wireless Mobile,QoS}, author = {T.Taleb and A.Nafaa and L.Murphy and K.Hashimoto and N.Kato and Y.Nemoto} }
@inproceedings { 216, title = {Terminal-oriented solutions for seamless service delivery via heterogeneous radio access networks (Invited Paper)}, booktitle = {Sarnoff Symposium 2007}, year = {2007}, abstract = {In this paper, options for providing seamless service delivery to mobile terminals via heterogeneous radio access networks are considered. Despite its current popularity, the Mobile IP solution for mobility management of mobile hosts is discounted due to problems associated with introducing the required network infrastructure and poor handover performance. Rather, the solution described here comprises of a number of key technologies working together. More specifically, the paper argues that the most appropriate solution comprises of the following: adaptive applications, an abstraction layer between application and transport layer, an intelligent transport layer with multi-homing and multi-path support and a means to obtain current state information about each of the available access networks. While work has been ongoing on each of these individual components little has been done to address how they can all be integrated and consider how they may perform in the context of different radio access technologies, potentially operated by different entities. This paper attempts to address some of these issues.}, keywords = {Heterogeneous wireless access networks, Handover, Mobile Networking}, author = {S. Murphy, M. Atiquzzaman, J. Fitzpatrick, J. Murphy} }
@proceedings { 400, title = {Towards a Media Independent Handover Based Approach to Heterogenous Network Mobility }, year = {2007}, publisher = {Performance Engineering Lab}, address = {Derry,Northern Ireland}, abstract = {In recent years the number and diversity of networks available to mobile computing devices has increased dramatically. It is now feasible for a device to support multiple networks such as 3G, 802.3, 802.11 and even 802.16. Given the diversity of these networks in terms of range and bandwidth, there is a need to define a seamless approach to network handover. While current 802 standards provide the facility to detect and select access points, these mechanisms are specific to individual network types. Moreover, current 802 standards do not provide the facility, or even the availability, of information triggers for handover. In order to address issues relating to heterogeneous network handover, the IEEE have proposed a new standard: 802.21, also referred to as Media Independent Handover. It is proposed that the emerging 802.21 standard will enable a mobile device to detect and initiate handover from one network to another. Currently the 802.21 standard is at draft stage and no implementations are available. This paper investigates how elements of the proposed standard can be utilised in conjunction with the transport layer Stream Control transmission Protocol (SCTP) in order to facilitate seamless network handover. We compare a pre-emptive 802.21 oriented switch strategy against standard fault reactive SCTP strategies. Results indicate that the 802.21 oriented strategy behaves more effectively than conservative SCTP switchover strategies, and has equivalent performance to aggressive SCTP switchover strategies.}, keywords = {Media Independent Handover, 802.21, SCTP, WLAN}, author = {E.Fallon and J.Murphy and L.Murphy and Y.Qiao and X.Xie and A.Hanley} }
@inproceedings { 442, title = {User Quality of Experience-Aware Multimedia Streaming over Wireless Home Area Network}, booktitle = {IEEE Vehicular Technology Conference}, year = {2007}, abstract = {For multimedia streaming over wireless networks, there is a trade-off between the capacity of the wireless links and the end-user perceived-quality, which can be affected by the compression scheme used, content characteristics and adaptation algorithm (if any). In this paper, this trade-off is investigated for streaming various motion content multimedia over an IEEE 802.11b-based Wireless-Home Area Network using the Quality-Oriented Adaptation Scheme (QOAS). QOAS performance is compared to that of a non-adaptive scheme when using MPEG-2 and MPEG-4 encoding in terms of average end-user perceived quality, number of streaming sessions concurrently supported, loss rate, delay, jitter and total throughput. Simulation results show that by using QOAS and MPEG-4 encoded streams a much higher number of concurrent streams are supported at an average quality above “good” level on the ITU-T five-point quality scale in comparison with other situations. In this case all the other streaming performance parameters were also significantly better.}, keywords = {Adaptive video streaming, Wireless Home Area Network, grading scheme, end-user perceived quality.}, author = {Gabriel-Miro Muntean and N.Cranley} }
@inproceedings { 213, title = {An Approach to Transport Layer Handover of VoIP over WLAN}, booktitle = {CCNC}, year = {2006}, month = {January 2006}, abstract = {In this paper a transport layer handover mechanism for Voice over Internet Protocol (VoIP) using the Stream Control Transmission Protocol (SCTP) is proposed. This handover mechanism utilizes the multi-homing feature of SCTP to allow connection to multiple wireless networks. Each available wireless network is probed with simulated VoIP data to obtain network performance metrics. Handover decisions are made based on the Mean Opinion Score (MOS) calculated from the ITU-T E-Model for voice quality assessment using the obtained measurements. Implementation and simulations were carried out using the NS2 network simulator. The results show the MOS obtained using the proposed handover mechanism on IEEE 802.11b WLAN access points (APs) under varying load conditions. High correlation is shown between the MOS from the proposed handover scheme and the MOS experienced by a VoIP node present in the network. A simulation showing an SCTP endpoint handover between AP’s is presented.}, keywords = {SCTP, E-Model, VoIP, Handover, Heterogeneous Networks}, author = {J. Fitzpatrick, S. Murphy and J. Murphy} }
@inproceedings { 161, title = {A Survey of Seamless Handover in Heterogeneous Radio Access Networks}, booktitle = {ACM/IEEE International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems}, year = {2006}, month = {10/2006}, publisher = {ACM/IEEE}, organization = {ACM/IEEE}, abstract = {This paper provides a detailed discussion of the problem of Seamless Handover in Heterogeneous Radio Access Networks. Several approaches to providing a handover solution have been proposed, some of which will be described and compared, in order to indicate possible directions for continuing to search for a seamless handover solution. Various problems are present in the existing solutions, and are discussed in this paper. }, keywords = {Seamless Handover, Heterogenous Networks, SCTP}, author = {C. Thorpe and L. Murphy} }
@inproceedings { 170, title = {Seamless Handover in Heterogeneous Radio Access Networks}, booktitle = {IT&T}, year = {2006}, month = {10/2006}, abstract = {This paper provides a detailed discussion of the problem of Seamless Handover in Heterogeneous Radio Access Networks. Brief descriptions of several wireless access technologies are included to provide some background information and to illustrate the importance of solving the seamless handover problem for network subscribers. Several approaches to providing a handover solution have been proposed, some of which will be described and compared, in order to indicate possible directions for continuing to search for a seamless handover solution. Various problems are present in the existing solutions, and are discussed in this paper. These problems are significant enough to warrant further investigation in the handover area, and leave scope for modifications and improvements.}, keywords = {Seamless Handover, Heterogenous Networks, SCTP}, author = {C. Thorpe and S. Murphy and L. Murphy} }
@inproceedings { 311, title = {A Relative Delay Minimization Scheme for Multiplayer Gaming in Diffrentiated Services Network}, booktitle = {ACM SIGCOMM Workshop on Network & System Support for Games}, year = {2006}, publisher = {PEL}, organization = {PEL}, abstract = {Multiplayer gaming over the Internet continues to grow in popularity, despite a lack of Quality of Service (QoS) mechanisms. Future QoS-aware networks such as those based on the Differentiated Services (DiffServ) framework will provide an opportunity for gamers to enhance their game-playing experience. An important QoS metric for networked games is a user’s delay relative to the delay of other users. In this paper, we propose a Relative Delay Minimization (RDM) algorithm for use in DiffServ environments. Simulation results are described and presented showing that the algorithm can reduce the Relative Delay Variation (RDV) between users in a DiffServ environment.}, keywords = {Network Games, Relative Delay, DiffServ, QoS}, author = {Carrig,B. and Denieffe,D. and Murphy,J.} }
@inproceedings { 439, title = {A Priority Based Adaptive Scheme for Wireless Multimedia Delivery}, booktitle = {IEEE International Conference on Multimedia & Expo(ICME)}, year = {2006}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In wireless multimedia streaming, there is a need to allow for client prioritisation in order to enable provision of end user perceived quality in direct relationship with client device importance. Currently, the same priority is given to all clients, independent of their characteristics, often resulting in unfair distribution of throughput. This paper proposes a priority-based wireless adaptive multimedia delivery scheme that enables client prioritisation during multimedia distribution over IP networks. The paper presents simulation results outlining the benefits of applying the algorithm, illustrating the improvement in bandwidth allocation and in overall end user perceived quality. The algorithm focuses on a residential wireless local area network and assigns static priorities based on device characteristics.}, keywords = {Wireless Communication,Multimedia Streaming}, author = {E.Casey and Gabriel-Miro Muntean} }
@proceedings { 393, title = {Automatic System for Linux Kernel Performance Testing}, year = {2006}, publisher = {Performance Engineering Lab}, address = {Ottawa,Canada}, abstract = {We introduce an automatic and open kernel testing system. We argue that only by opening a test system to the community and aggregating the results from a variety of sources can one get a comprehensive picture of the kernel’s performance status. Our system can also help identifying problems with specific parts of code whether it is a device driver, some other module, or platform-specific code. Design of both client and server parts of the system is described. Since system is open, specific emphasis in client part is placed on successful automation and configuration of the testing process. The emphasis of the server part is placed on regression detection and accidental/malicious input elimination. Current implementation status is presented.}, keywords = {Kernel System,Linux}, author = {A.Ufimtsev and L.Murphy} }
@proceedings { 418, title = {Addressing the Link Adaptation Problem for VoWLAN using Codec Adaptation}, year = {2006}, abstract = {In this paper a scheme is proposed to deal with congestion problems that can arise due to Link Adaptation (LA) in Wireless Local Area Networks (WLANs) in the presence of VoIP traffic. The proposed scheme operates by first determining if LA has resulted in the system becoming congested. If not, no further action is taken. However, if, LA has resulted in an overloaded system, the voice codec of the handset which has undergone LA is adapted so as to restore the system to its earlier state, thereby alleviating the congestion. This is achieved by specifically adapting the codec so as to maintain approximately the same level of medium usage as was used prior to the LA. The proposed scheme was evaluated on an experimental test-bed and results show that the codec adaptation was very effective at overcoming the problem of LA.}, keywords = {Voice over IP (VoIP), IEEE 802.11, Admission}, author = {P.McGovern and S.Murphy and L.Murphy} }
@proceedings { 427, title = {Authoring Model for Quality of Experience-aware adaptive hypermedia systems}, year = {2006}, address = {Dublin,Ireland}, abstract = {This paper presents a novel authoring framework for Quality of Ex-perience (QoE) aware Adaptive Hypermedia Systems. It extends the LAOS au-thoring model in order to consider delivery performance issues. The paper formalises and exemplifies the newly proposed QoE extensions for the LAOS Adaptation and Presentation Models that include QoE Characteristics and QoE Rules layers.}, keywords = {QoE,LAOS}, author = {Muntean,C.H and Muntean,G.M and Cristea} }
@proceedings { 431, title = {Cost-Oriented Selection & Delivery of E-Content over Various Wireless Networks}, year = {2006}, address = {Sydney,Australia}, abstract = {As wireless technologies are competing with wired solutions in delivering information, there is a clear shift of e-learning towards mobile learning (m-learning). M-learning, which involves both wireless communications and mobile computing, provides learning opportunities to people without wire-based Internet infrastructure or that are continually on the move. At the same time, a large number of educational e-content providers produce and distribute materials that cover a wide range of topics (very often different providers may cover the same topic), differ in quality or presentation format and have different cost. In this context this paper presents a COST-efficient PERsonalised Wireless based E-LEARNing Service (Cost/We-Learn) that provides support for the selection and distribution of personalised educational rich media content (e.g. multimedia, pictures, graphics and text) that best suits user goals, device and cost constraints. Assuming that the user has simultaneous access to multiple wireless networks, Cost/We-Learn enables the selection of that access network over which the selected personalised content will be delivered such as the overall cost matches user budget constraints. This overall cost includes both the price paid for the selected educational material and the delivery cost.}, keywords = {Wireless Communication,E-Learning,Cost-Oriented}, author = {Muntean,C.H. and Muntean,G.M.} }
@article { 420, title = {Dynamic Content-Based Adaptation of Streamed Multimedia,Intelligence-based Adaptation for Ubiquitous Multimedia Communications}, journal = {Journal of Network & Computer Applications}, volume = {30}, year = {2006}, pages = {983-1006}, publisher = {Science Direct}, abstract = {Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptation decisions. We show that an optimal adaptation trajectory (OAT) through the set of possible encodings exists, and that it indicates how to adapt encoding quality in response to changes in network conditions in order to maximise user-perceived quality. The OAT is related to the characteristics of the content, in terms of spatial and temporal complexity. We describe a method to automatically determine the OAT in response to the time-varying characteristics of the content. In this way, as the characteristics of the content change over time, the system can dynamically and intelligently adjust the adaptation process in order to maximise the user-perceived quality. The OAT can be used with any sender-based transmission adaptation policy. We demonstrate content-based adaptation using the OAT in a practical system using two different adaptation algorithms. Furthermore, we show how this form of adaptation can result in differing adaptation behaviour not only as a result of the dynamics of the content but also as a result of the adaptation algorithm being used. Finally, we show how increased feedback frequency does not necessarily improve the behaviour of the adaptation algorithm being used.}, keywords = {User perception; Video quality; Adaptive systems; Multimedia}, author = {N.Cranley and L.Murphy and P.Perry} }
@inproceedings { 313, title = {Delivery of On-Demand Video Services in Rural Areas via IEEE 802.16 Broadband Wireless Access Networks}, booktitle = {ACM 2nd Workshop on Wireless Multimedia Networking & Performance Modelling }, year = {2006}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A simulation study of delivery of streaming video on-demand via IEEE 802.16 based technologies is described. A number of scenarios are simulated which are representative of rural area deployments of such technologies. The study finds that IEEE 802.16 can support up to 9/10 simultaneous users streaming typical cinematic video content in CIF resolution, 24 frames/s, at average rates of around 750 kbps. Further, the study demonstrates the utility of H.264/AVC Scalable Video Coding (SVC) and a buffer-based congestion control algorithm in an adaptive video streaming solution.}, keywords = {IEEE 802.16, video streaming, scalable video coding}, author = {Hillestad,O.I. and Perkis,A. and Genc,V. and Murphy,S. and Murphy,J.} }
@inproceedings { 318, title = {Delivering Quality of Service for Gaming Applications in Best Effort Networks}, booktitle = {13th International Conference on Telecommunications}, year = {2006}, publisher = {Irish Research Council}, organization = {Irish Research Council}, abstract = {This paper describes a scheduler which provides non-elevated Quality of Service (QoS) for two different classes of traffic. A Delay-Sensitive (DS) class receives a low delay service at the expense of an increased probability of packet loss. The non-DS traffic receives at least the same level of throughput as it would in an ordinary best effort network. The design of the scheduler is presented and contrasted with similar schedulers such as the Alternative Best Effort (ABE) service. Simulation results for a network carrying a mixture of FTP and Quake 3 multiplayer gaming traffic are also shown. It was discovered that even for a heavily-loaded network, with a large proportion of non-DS traffic, there are benefits for interactive games traffic availing of the DS service.}, keywords = {Networked Games, Non-elevated QoS, Quality of Service}, author = {Carrig,B. and Denieffe,D. and Murphy,J.} }
@article { 410, title = {End-User Quality of Experience Oriented Adaptive E-learning System}, journal = {Journal of Digital Information}, volume = {7}, year = {2006}, pages = {1}, publisher = {Digital Information Research Foundation}, abstract = {In the context of new devices and with a variety of network technologies that allow access to the Internet, the providers of e-learning materials have to ensure that the users have a positive experience using their e-learning systems and they are happy to re-use them. Adaptive Hypermedia research aims to provide personalised educational material that ensures a positive learning experience for the end-users. However, user experience is dependent not only on the content served to them, but also on the user perceived performance of the e-learning system. This leads to a new dimension of individual differences between Web users: the end-user Quality of Experience (QoE). We have proposed a solution for Adaptive Hypermedia Systems (AHS) that provides satisfactory end-user QoE through the use of a new QoE layer. This layer attempts to take into account multiple factors affecting QoE in relation to the delivery of a wide range of Web components such as text, images, video, audio.
The effectiveness of our QoE layer has been tested in comparison to a standard educational AHS and the results of these tests are presented in this paper. Different educational-based evaluation techniques such as learner achievement analysis, learning performance assessment, usability survey and correlation analysis between individual student performance and judgment on system usability were applied in order to fully assess the performance of the proposed QoE layer. Results of the tests showed that the use of the QoE layer brought significant improvements in terms of user learning performance, system usability and user satisfaction with the personalised e-learning system while not affecting the user learning achievement }, keywords = {end-user QoE, adaptive hypermedia, e-learning, end-user perceived performance, learning performance }, author = {C.H.Muntean and J.McManis} }
@inproceedings { 312, title = {End-point Synchronisation & Handover For Multi-homed Services}, booktitle = {IEE Proceedings-Communications}, year = {2006}, publisher = {PEL}, organization = {PEL}, abstract = {It is proposed to implement a synchronised routing table at the transport layer, referred to as an Association Routing Table (ART), to improve the performance of multi-homed transport protocols. An algorithm is described that ensures that the routing tables can be synchronised, which is then used to implement a handover mechanism. The ART is implemented within SCTP. It is shown that by using a synchronised ART, it is possible to implement failover in cases where standard SCTP cannot, con¯gurations are more resilient to network errors, and it is possible to perform a handover without any network support.}, keywords = {Multi-homing, routing, transport layer, SCTP, handovers}, author = {Noonan,J. and Perry,P. and Murphy,J.} }
@inproceedings { 314, title = {Evaluation of an Intelligent Utility-Based Strategy for Dynamic Wireless Network Selection}, booktitle = {Autonomic Management of Mobile Multimedia Services}, year = {2006}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In the case of next generation wireless networks, different users with various multi-homed personal wireless devices will aim to exploit the full potential of the choice of services and applications available over different radio access networks. In their selection of a certain radio access network consumers will consider money and delay preferences for the current application and will rely on intelligent network-selection decision strategies to aid them in their choice. This paper describes the evaluation of an intelligent utility-based strategy for network selection in a multi-access network situation for transfer of large non real-time data files. A number of scenarios are examined which compare the proposed network selection strategy against other possible strategies. Test results show how by using this network selection strategy significant benefits in terms of combined average delay and cost per file transferred as well as transfer efficiency are obtained.}, keywords = {Heterogeneous Wireless Networks, Multi-homed Radio Terminals, User-centric Network Selection.}, author = {Ormond,O. and Muntean,G. and Murphy,J.} }
@inproceedings { 320, title = {Economic Model for Cost Effective Network Selection Strategy in Service Oriented Heterogenous Wireless Network Environment}, booktitle = {10th IEEE/IFIP Network Operations & Management Symposium}, year = {2006}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {This paper describes and formalises the Service Oriented Heterogeneous Wireless Network Environment (SOHWNE)A the future service provision and delivery environment that will support ubiCuitous user access anywhere at any time from diverse devices to a broad range of services. These services can be offered by third parties and can be accessed via one of many available networks. This paper also proposes and describes a novel algorithm for intelligent costoriented and performance-aware selection between available networks. This user-centric strategy focuses on the maximisation of consumer surplus when selecting the best available connection for transferring non real-time dataA with user specified time constraintsA in a user-centric SOHWNE.}, keywords = {Consumer SurplusA Decision-making StrategiesA Multi-provider Network EnvironmentA Non real-time Data.}, author = {Ormond,O. and Murphy,J. and Muntean,G.} }
@inproceedings { 451, title = {Efficient Delivery of Multimedia Streams over Broadband Networks using QOAS}, booktitle = {IEEE Trans. on Broadcasting}, year = {2006}, abstract = {Quality Oriented Adaptation Scheme (QOAS) is compared against other adaptive schemes such as TCP Friendly Rate Control Protocol (TFRCP), Loss-Delay-based Adaptation Algorithm (LDA+), and a nonadaptive (NoAd) solution when streaming multiple multimedia clips with various characteristics over broadband networks. Streaming efficiency is assessed in terms of loss rate, bandwidth utilization, number of concurrent clients and end-user perceived quality. Simulation results show that using QOAS a significantly higher number of simultaneous clients can be served than when using the other schemes given a target average end-user quality. This is while having higher bandwidth utilization. Testing results also indicate that higher performance is achieved when streaming to the same number of clients using QOAS than when other solutions are used.}, keywords = {Adaptive streaming, congestion control, end-user}, author = {Gabriel-Miro Muntean} }
@proceedings { 397, title = {Endpoint Admission Control for VoIPoWLAN }, year = {2006}, address = {Portugal}, abstract = {In this paper a Call Admission Control (CAC) scheme for Voice over Internet Protocol (VoIP) over a Wireless Local Area Network (WLAN) is proposed. The CAC scheme is based on the Endpoint Admission Control (EAC) paradigm where the endpoints, i.e. the WLAN terminals, probe the network to ascertain if the call can be supported with acceptable Quality of Service (QoS). The proposed scheme was evaluated on an experimental test-bed and test results show that correct Admission Control (AC) decisions were made under various network configurations.}, keywords = {Voice over IP (VoIP), Wireless Local Area Network (WLAN), IEEE 802.11, Admission Control (AC)}, author = {P.McGovern and S.Chung and S.Murphy and L.Murphy} }
@proceedings { 429, title = {Fine Grained Content-Based Adaptation Mechanism for Providing High End-User Quality of Experience with Adaptive Hypermedia Systems }, year = {2006}, abstract = {New communication technologies can enable Web users to access personalised information “anytime, anywhere”. However, the network environments allowing this “anytime, anywhere” access may have widely varying performance characteristics such as bandwidth, level of congestion, mobility support, and cost of transmission. It is unrealistic to expect that the quality of delivery of the same content can be maintained in this variable environment, but rather an effort must be made to fit the content served to the current delivery conditions, thus ensuring high Quality of Experience (QoE) to the users. This paper introduces an end-user QoE-aware adaptive hypermedia framework that extends the adaptation functionality of adaptive hypermedia systems with a fine-grained content-based adaptation mechanism. The proposed mechanism attempts to take into account multiple factors affecting QoE in relation to the delivery of Web content. Various simulation tests investigate the performance improvements provided by this mechanism, in a home-like, low bit rate operational environment, in terms of access time per page, aggregate access time per browsing session and quantity of transmitted information.}, keywords = {QoE,WebUsers,Bandwidth}, author = {Muntean,C.H. and McManis,J.} }
@proceedings { 430, title = {Framework for Interactive Personalised IPTV for Entertainment}, year = {2006}, abstract = {Interactive IPTV is seen as the future for delivering TV services as it brings all the benefits of computer-based IP networking to the residential viewers. This paper presents the iPersonal IPTV framework that enhances the existing interactive IPTV solution with viewer-oriented personalisation and network and device-based adaptation. This framework is proposed in order to provide significant benefits in terms of viewers' Quality of Experience and to increase their satisfaction. The iPersonal IPTV framework is exemplified in the area of entertainment distribution to remote residential users.}, keywords = {Personalisation, network and device adaptation, IPTV, Quality of Experience, user modeling.}, author = {Muntean,C.H. and Muntean,G.M.} }
@article { 396, title = {Incorporating User Perception in Adaptive Video Streaming Systems}, journal = {Digital Multimedia Perception & Design}, volume = {May 2006}, year = {2006}, pages = {860-861}, publisher = {Idea Group}, abstract = {There is an increasing demand for streaming video applications over both the fixed Internet and wireless IP networks. The fluctuating bandwidth and time-varying delays of best-effort networks makes providing good quality streaming a challenge. Many adaptive video delivery mechanisms have been proposed over recent years; however, most do not explicitly consider user-perceived quality when making adaptations, nor do they define what quality is. This chapter describes research that proposes that an optimal adaptation trajectory through the set of possible encodings exists, and indicates how to adapt transmission in response to changes in network conditions in order to maximize user-perceived quality.}, keywords = {Video Streaming,Internet,IP Networks}, author = {N.Cranley and L.Murphy} }
@proceedings { 392, title = {Introducing Performance Engineering by means of Tools & Practical Exercises}, year = {2006}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Many software engineers complete their education without an introduction to the most basic performance engineering concepts. IT specialists need to be educated with a basic degree of performance engineering knowledge, so they are aware of why and how certain design and development decisions can lead to poor performance of the resulting software systems. To help address this need, the School of Computer Science and Informatics at University College Dublin offered a final year undergraduate/first year postgraduate module on ”Performance of Computer Systems” in Autumn 2005. In this paper we document how performance engineering was introduced to the students through practical exercises, and how these exercises relate to industry problems.}, keywords = {Software,J2EE}, author = {A.Ufimtsev and T.Parsons and L.Patcas and J.Murphy and L.Murphy} }
@proceedings { 394, title = {Impact of Virtual Managers on Performance of J2EE Applications}, year = {2006}, publisher = {Performance Engineering Lab}, address = {Sweden}, abstract = {We investigate the impact of Operating System's Virtual Memory Managers (VMMs) on performance of enterprise applications. By taking various popular branches of the Linux kernel and modifying their VMM settings, one can see the e®ects it introduces on ECPerf J2EE Benchmark. JBoss application server is used to run ECPerf. Our tests show that even the change of one parameter in VMM can have signi¯cant performance impacts. Performance of various kernel branches is compared. Parameter sensitivity and in°uence of speci¯c settings are presented.}, keywords = {Operating System,J2EE,Linux}, author = {A.Ufimtsev and A.Kucherenko and L.Murphy} }
@proceedings { 316, title = {Model Driven Distribution Pattern Design for Dynamic Web Service Compositions}, year = {2006}, publisher = {Performance Engineering Lab}, abstract = {Web service compositions are often used to realise servicebased enterprise applications. These enterprise systems are built from many existing discrete applications, often legacy applications exposed using Web service interfaces. Acceptance of these systems is often constrained by non-functional aspects, such as Quality of Service (QoS). A number of factors a�ect the QoS of an enterprise system, including availability, scalability and performance. There are a number of architectural con�gurations or distribution patterns, which express how a composed system is to be deployed. These distribution patterns have a direct impact upon the QoS of the composition. However, the amount of code required to realise these distribution patterns is considerable. Additionally, there is an increased deployment time associated with setting up di�erent distribution patterns. We therefore propose a novel approach which combines a Model Driven Architecture using UML 2.0 for modeling and subsequently generating Web service compositions, with a method for achieving dynamic decentralised interaction amongst services with reduced deployment overheads. These approaches combined provide for the generation of dynamic Web service compositions driven by a distribution pattern model.}, keywords = {Distribution patterns, Web services, compositions, decentralisation, MDA}, author = {Barrett,R. and Pahl,C. and Patcas,L.M. and Murphy,J.} }
@inproceedings { 315, title = {Non-Intrusive End to End Run-time Path Tracing for J2EE Systems}, booktitle = {IEE Proceedings-Software}, year = {2006}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {An end-to-end runtime path-tracing approach for J2EE systems has been introduced. The approach is non-intrusive and thus does not require instrumentation of middleware or application source code. The implementation of the system has been realised in the COMPAS Java end-to-end monitoring tool that extends and integrates a number of open source projects. The first set of results shows the performance overhead associated with the tool. Further results show the portability of this approach, by applying it to a number of different application server implementations. Finally, it is also shown that runtime paths collected by the implementation can be used for reasoning about the overall system structure and design of complex enterprise applications.}, keywords = {IEEE ,Server}, author = {Parsons,T. and Mos,A. and Murphy,J.} }
@proceedings { 391, title = {Performance Modelling of a JAVAEE Component Application using Layered Queuing Networks:Revised Approach & a Case Study}, year = {2006}, publisher = {Performance Engineering Lab}, address = {Portland,USA}, abstract = {Nowadays component technologies are an integral part of any enterprise production environment. Performance and scalability are among the key properties of such systems. Using Layered Queuing Networks (LQN), one can predict the performance of a component system from its design. This work revises the approach of using LQN templates and offers a case study by using the revised approach to model a realistic component application. Both strong points and shortcomings of the approach are discussed.}, keywords = {performance modeling, JavaEE, component systems, ECPerf, Layered Queuing Network.}, author = {A.Ufimtsev and L.Murphy} }
@proceedings { 395, title = {Protection Againest Link Adaptation for VoWLAN}, year = {2006}, publisher = {Performance Engineering Lab}, address = {Myconos,Greece}, abstract = {In this paper a scheme is proposed to deal with the problem of Link Adaptation (LA) of an ongoing call in a Voice over Wireless Local Area Network (VoWLAN) environment. The scheme operates by dropping the call from the system if the LA affects the call quality of the other ongoing calls. The proposed scheme was evaluated on an experimental test-bed and results show that it protected the quality levels of the other ongoing calls under various network configurations.}, keywords = {Voice over IP (VoIP), IEEE 802.11, Admission Control (AC), Link Adaptation (LA)}, author = {P.McGovern and S.Murphy and L.Murphy} }
@proceedings { 428, title = {Performance Enhancement for Open Corpus Adaptive Hypermedia Systems}, year = {2006}, address = {Dublin,Ireland}, abstract = {Adaptive Hypermedia Systems adjust the content to best suit users’ personal characteristics, but rarely consider delivery performance. Performance issues are even more significant in distributed architectures such as that of an Open Corpus Adaptive Educational Hypermedia System (OAEHS). This paper introduces a Performance Oriented Adaptation Agent (POAA) that enhances OAEHS by taking into consideration not only user personal characteristics but also network delivery conditions in the content selection process. The usage of POAA is expected to bring significant delivery performance improvements in terms of learner satisfaction and learning outcome.}, keywords = {OAEHS,POAA,Hypermedia}, author = {Rovcanin,L. and Muntean,C.H. and Muntean,G.M.} }
@inproceedings { 215, title = {RTS/CTS Based Endpoint Admission Control for VoIP Over 802.11e}, booktitle = {MMNS}, year = {2006}, abstract = {In this paper an endpoint-based admission control mechanism for VoIP over WLAN is proposed. The mechanism operates by first measuring the utilisation of the channel and comparing this to a pre-determined threshold, if the channel utilisation exceeds this threshold, the call is rejected. One important aspect of the mechanism is that it can operate in the presence of hidden terminals. This is done by using the Request-to-Send/Clear-to-Send WLAN signalling to determine channel utilisation. The scheme is designed to be flexible; it can operate with heterogeneous data rates, with varying traffic types and in the presence of legacy 802.11 nodes. The scheme was developed and evaluated using the Qualnet network simulator. An empirical approach was used to determine appropriate admission thresholds. Then, simulations were performed to demonstrate the successful operation of the scheme.}, keywords = {Call Admission Control, VoIP, 802.11e, RTS/CTS}, author = {J. Fitzpatrick, S. Murphy, J. Murphy} }
@inproceedings { 319, title = {Stall & Path Monitoring Issues in SCTP,IEEE Infocom}, booktitle = {Conference on Computer Communications}, year = {2006}, publisher = {UCD}, organization = {UCD}, abstract = {This paper presents how SCTP can stall in multihomed scenarios during failover and under certain circumstances. A stall is where an SCTP end-point ceases to communicate for an extended period of time, but does not report any error to the upper layer. This paper presents two different sets of circumstances where a stall can occur: firstly when there is an underestimation of the Retransmission Time-Out (RTO) value for a redundant network path; and secondly when a network error occurs that causes only SACKs to be lost, which confuses the SCTP sender about which network path is operational. Solutions to both of these stalls are presented that include modifying the RTO value, applying Karn’s algorithm to path monitoring and ensuring the destination address selection policy for SACKs is changed. This paper also presents a mechanism to de-couple data acknowledgement and path monitoring when using multi-homed transport protocols, which should remove the ambiguity about path monitoring and offers a universal solution to the stall.}, keywords = {SCTP}, author = {Noonan,J. and Perry,P. and Murphy,S. and Murphy,J.} }
@proceedings { 214, title = {SCTP based Handover Mechanism for VoIP over IEEE 802.11b Wireless LAN with Heterogeneous Transmission Rates}, year = {2006}, abstract = {In this paper a transport layer handover mechanism for Voice over Internet Protocol (VoIP) in 802.11b using the Stream Control Transmission Protocol (SCTP) is proposed. The multi-homing feature of SCTP is used to allow connections to several 802.11b Access Points (AP's). Probing packets that model VoIP encoded data at various transmission rates are used to obtain quality metrics from each of the available networks. Handover decisions are made based on the Mean Opinion Score (MOS) calculated from the ITU-T E-Model for voice quality assessment using the obtained measurements. The handover mechanism is shown to operate in 802.11b networks with heterogeneous transmission rates using multiple VoIP codecs. The results show a high correlation between the MOS predicted by the proposed mechanism and the MOS experienced by a VoIP call present in the network. Results verify the accurate operation of the scheme using multiple VoIP codecs at various transmission rates. A simulation showing an SCTP endpoint handover between heterogeneous transmission rate AP's is presented.}, keywords = {SCTP, VoIP}, author = {J. Fitzpatrick, and S. Murphy, and J. Murphy,} }
@inproceedings { 321, title = {The 2nd International Middleware Doctoral Symposium:Detecting Performance Antipatterns in Component-Based Enterprise Systems}, booktitle = {IEEE Distributed Systems Online }, year = {2006}, publisher = {PEL}, organization = {PEL}, abstract = {Internet-enabled enterprise applications often fail to meet their performance requirements. This can lead to development delays or, even worse, loss of business due to customer dissatisfaction with sluggish or unreliable service. Inefficient enterprise systems are often the result of system developers making incorrect or suboptimal design decisions. Such decisions occur because today’s enterprise applications are extremely large and complex, and developers often don’t completely understand the entire application. Consequently, they often don’t completely understand the performance implications of their design decisions, and as a result, systems frequently fail to meet their performance agreements. }, keywords = {Performance Oriented,}, author = {Parsons,T. and Murphy,J.} }
@proceedings { 426, title = {The Value of QoE-based adaptation approach in educational hypermedia:Empirical evaluation}, year = {2006}, abstract = {This paper reports the results of a comparison-based empirical study on the applicability of the end-user Quality of Experience-based content adaptation mechanism in adaptive educational hypermedia. The focus of the paper will be the experiment itself: the initial settings, testing scenarios and the results. We will show that for low bit rate connections the QoE-based adaptation decreases study session time, information processing time per page and the number of re-visits to a page, it maintains similar learning outcomes while also improving the user quality of experience and satisfaction with the system. Finally we will comment on the results and interpret them.}, keywords = {QoE}, author = {Muntean,C.H. and McManis,J} }
@article { 419, title = {User Perception of Adapting Video Quality}, journal = {International Journal of Human-Computer Studies/Knowledge Acquisition}, volume = {64}, year = {2006}, pages = {637-647}, publisher = {Science Direct}, abstract = {In general, video quality adaptation and video quality evaluation are distinct activities. Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptation decisions. Equally, video quality evaluation techniques are not designed to evaluate instantaneous quality where the quality is changing over time. We propose that an Optimal Adaptation Trajectory (OAT) through the set of possible encoding exists, and that it indicates how to adapt encoding quality in response to changes in network conditions in order to maximize user-perceived quality. The subjective and objective tests carried out to find such trajectories for a number of different MPEG-4 video clips are described. Experimental subjective testing results are presented that demonstrate the dynamic nature of user perception with adapting multimedia. The results demonstrate that adaptation using the OAT out-performs conventional adaptation strategies in which only a single aspect of the video quality is adapted. In contrast, the OAT provides a mechanism to adapt multiple aspects of the video quality thereby giving better user-perceived quality in both the short and long term.}, keywords = {Video quality; Evaluation/methodology; Perception; Subjective and objective quality; Adaptation}, author = {N.Cranley and P.Perry and L.Murphy} }
@inproceedings { 317, title = {Utility-based Intelligent Network Selection in Beyond 3G Systems}, booktitle = {IEEE International Conference on Communications}, year = {2006}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Development in wireless access technologies and multihomed personal user devices is driving the way towards a heterogeneous wireless access network environment. Success in this arena will be reliant on the ability to offer an enhanced user experience. Users will plan to take advantage of the competition and always connect to the network which can best service their preferences for the current application. They will rely on intelligent network selection decision strategies to aid them in their choice. The contribution of this paper is to propose an intelligent utility-based strategy for network selection in this multi-access network scenario. A number of utility functions are examined which explore different user attitudes to risk for money and delay preferences related to their current application. For example we show that risk takers who are willing to pay more money get a better service.}, keywords = {Wireless Networks,3G}, author = {Ormond,O. and Murphy,J. and Muntean,G.} }
@article { 383, title = {Adaptive VoIP playout Scheduling :A new method for assesing user satisfaction}, journal = {IEEE Internet Computing}, volume = {July 2005}, year = {2005}, pages = {28-34}, publisher = {IEEE}, abstract = {Delay and packet loss dramatically affect the quality of a voice-over-IP (VoIP) call and depend on the playout buffer scheme implemented at the receiver. The choice of playout algorithm can’t be based on statistical metrics without considering the perceived end-to-end conversational speech quality. The authors present a method for evaluating various playout algorithms that extends the Emodel concept by estimating user satisfaction from time-varying transmission impairments. This article evaluates several playout algorithms and shows a correspondence between their results and those obtained via statistical loss and delay metrics.}, keywords = {Delay,Jitter,Packet Loss}, author = {M.Narbutt and A.Kelly and L.Murphy and P.Perry} }
@inproceedings { 301, title = {Automating the Performance Management of Component-Based Enterprise Systems through the use of Redundancy}, booktitle = {IEEE/ACM International Conference on Automated Software Engineering(ASE-2005)}, year = {2005}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Component technologies are increasingly being used for building enterprise systems, as they can address complex functionality and flexibility problems and reduce development and maintenance costs. Nonetheless, current component technologies provide little support for predicting and controlling the emerging performance of software systems that are assembled from distinct components. This paper presents a framework for automating the performance management of complex, component-based systems. The adopted approach is based on the alternate usage of multiple component variants with equivalent functional characteristics, each one optimized for a different running environment. A fully-automated framework prototype for J2EE is presented, along with results from managing a sample enterprise application on JBoss. A mechanism that uses monitoring data to learn and automatically improve the framework’s management behaviour is proposed. The framework imposes no extra requirements on component providers, or on the component technologies.}, keywords = {autonomic management, J2EE, decision policies}, author = {Diaconescu,A. and Murphy,J.} }
@inproceedings { 303, title = {A Low Complexity Algorithm for Statistically Based Estimation of Average IP Packet Delay in Cellular Data Networks}, booktitle = {International Teletraffic Congress,ITC-19}, year = {2005}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A new, low computation complexity technique for prediction of the average delay of IP packets, transported over cellular data networks with SR-ARQ loop, is presented in this paper. This prediction takes into account the SR-ARQ in�uence on the average IP packet delay, assuming that the MAC works with a static schedule policy (offering a �xed periodic access to radio resources). This assumption allows the use of this prediction as a link performance descriptor that is complementary to C/I, BER and BLER. A series of simulations and calculations have been performed to analyze the error introduced by the prediction. The results of these tests prove that the proposed method introduces a negligible prediction error, while the computation complexity is kept at a reasonable low level. Keywords:ARQ, IP packet delay, wireless QoS}, keywords = {IP packet delay, wireless QoS, mobile multimedia}, author = {Graja,H. and Peery,P. and Murphy ,J. } }
@inproceedings { 307, title = {A Statistical Estimation of Average IP Packet Delay in Cellular Data Networks}, booktitle = {IEEE Wireless Communication & Network Conference}, year = {2005}, publisher = {University College Dublin}, organization = {University College Dublin}, abstract = {A novel technique for estimating the average delay experienced by an IP packet in cellular data networks with an SRARQ loop is presented. This technique uses the following input data: a statistical description of the radio channel, ARQ loop design parameters and the size of a transported IP packet. An analytical model is derived to enable a closed form mathematical estimation of this delay. To validate this model, a computer based simulator was built and tests showed good agreement between the simulation results and the model. This new model is of particular interest in predicting the packet delay for conversational traffic such as that used for VoIP applications.}, keywords = {ARQ,IP packet delay, wireless QoS, mobile multimedia}, author = {Graja,H. and Peery,P. and Murphy ,J. } }
@proceedings { 378, title = {Adapting WLAN MAC Parameters to Maximise VoIP Call Capacity }, year = {2005}, abstract = {This work describes a detailed simulation-based study of the performance of an IEEE 802.11e Medium Access Con- trol (MAC) layer over an IEEE 802.11g Physical (PHY) layer. The study focuses on the number of simultaneous bidirectional G.711 Voice over IP (VoIP) calls that can be supported by a Wireless Local Area Network (WLAN) us- ing the Extended Rate PHY - Orthogonal Frequency Division Modulation (ERP-OFDM) mode of 802.11g. A new scheme for adapting the WLAN MAC parame- ters is proposed in this work. The new scheme dynamically adapts the Contention Window (CW) based on the retrans- mission rate of the system. In addition, an adaptive Trans- mission Opportunity (TXOP) mechanism aids in balancing the uplink and downlink tra±c levels and so provides the equality in uplink and downlink performance that is required for bidirectional VoIP tra±c. The proposed scheme can thus maintain acceptable levels of QoS for higher call capacities, increasing the overall VoIP capacity of the system.}, keywords = {Wireless LAN, VoIP, Medium Access Control, Quality of Service, Parameter Adaptation.}, author = {G.Hanley and S.Murphy and L.Murphy} }
@proceedings { 386, title = {A simulation model of a multi-server EJB system}, year = {2005}, publisher = {Performance Engineering Lab}, address = {St.Louis,Missouri,USA}, abstract = {Despite the fact that EJB (Enterprise Java Beans) is a widely used technology, research in the area of performance modelling of EJB application servers is quite sparse. This paper will describe how WorkbenchTM, an advanced simulation modelling tool, can be used to build a scalable model of a multi-server EJB system that allows users to input variables that describe interactions and their constituent methods, as well as system parameters. The model will output the average time for each given user interaction and allow users to seek system improvements by changing the system parameters and workloads.}, keywords = {EJB,JavaBeans}, author = {D.McGuinness and L.Murphy} }
@inproceedings { 306, title = {Cost-based burst dropping strategy in Optical Burst Switching Networks}, booktitle = {IEEE 7th International Conference on Transport Optical Networks}, year = {2005}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Optical Burst Switching (OBS) is a new paradigm for future all-optical networks. Intentional burst dropping is one of techniques used to achieve desired quality of service. In this paper we note that some bursts are more likely to cause contention. We propose a cost function that can be used to predict the likelihood that a given burst will interfere with other traffic, then we explain how, by using this information a new burst dropping strategy can be designed. We compare our method with a random burst dropping technique and show that the cost-based approach offers a significant performance improvement. Keywords: Optical Burst Switching (OBS), burst dropping, quality of service.}, keywords = {Optical communications}, author = {Klusek,B. and Murphy,J. and Barry,L.P.} }
@inproceedings { 309, title = {Cost-based Wavelength Allocation Algorithms in Optical Burst Switching Networks}, booktitle = {APOC 2004,SPIE,Optical Transmission,Switching & Subsystems II,LNCS}, year = {2005}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Optical Burst Switching(OBS) is a new paradigm for future all optical networks.It has been noted that performance of an OBS nodedepends on the wavelength algorithms called cost based algorithms.We note that bursts compete for more type of resources than wavelength alone.For example if a given burst is to be allocated successfully,a Fiber Delay Line (FDL) or a wavelength convertor may have to be used.It can be expected however that the set of available resources will be limited.If at a given time all the convertors are used,then any arriving burst will have to be allocated on the same wavelength-if it is available.Similarly the unavailablity of FDLs will decrease the probablity of burst being accepted.In a cost-based algorithm,each resource is assigned a metric(or price).Channels arepriced according to their suitablity for a particular burst.When a control packet arrives at a core node,all the possible ways of handling the corresponding burst are found(the outgoing channel,with or without a FDL or wavelength converter),and the one with the lowest metric is chosen.To show how the performance of a cost-based algorithm compares to other algorithm we present the result of our simulations for a node with full conversion capablity and a shared FDL.}, keywords = {Wavelength}, author = {Klusek,B. and Murphy,J. and Perry,P.} }
@proceedings { 384, title = {Exploring the Extent & Impact of Playout Adjustments within VoIP Applications on MOS Scores}, year = {2005}, address = {Prague,Czech Republic}, abstract = {Delay and packet loss dramatically affect the quality of a voice-over-IP (VoIP) call and depend on the playout buffer scheme implemented at the receiver. The choice of playout algorithm can’t be based on statistical metrics without considering the perceived end-to-end conversational speech quality. The authors present a method for evaluating various playout algorithms that extends the Emodel concept by estimating user satisfaction from time-varying transmission impairments. This article evaluates several playout algorithms and shows a correspondence between their results and those obtained via statistical loss and delay metrics.}, keywords = {Delay and packet loss dramatically affect the quality of a voice-over-IP (VoIP) call and depend on the playout buffer scheme implemented at the receiver. The choice of playout algorithm can’t be based on statistical metrics without considering the perceiv}, author = {H.Melvin and L.Murphy} }
@article { 300, title = {Middleware Benchmarking:Approaches,Results,Experiences,}, journal = {Concurrency & Computation-Practice & Experience}, volume = {17(15)}, year = {2005}, pages = {1799-1805(7 pages)}, publisher = {John Wiley & Sons}, abstract = {The report summarizes the results of the Workshop on Middleware Benchmarking held during OOPSLA 2003. The goal of the workshop was to help advance the current practice of gathering performance characteristics of middleware implementations through benchmarking. The participants of the workshop have focused on identifying requirements of and obstacles to middleware benchmarking and forming a position on the related issues. Selected requirements and obstacles are presented, together with guidelines to adhere to when benchmarking, open issues of current practice, and perspectives on further research}, keywords = {middleware benchmarking; middleware performance; middleware scalability; middleware evaluation; middleware benchmark design; benchmarking guidelines; benchmarking measurement; benchmarking metrics; OOPSLA 2003 workshop}, author = {Brebner,P. and Cecchet,E. and Marguerite,J. and Tuma,P. and Ciuhandu,O. and Dufour,B. and Eeckhout,L. and Frenot,S. and Krishna,A.S. and Murphy,J. and Verbrugge,C.} }
@inproceedings { 389, title = {Method Input Parameters & Performances of EJB Applications}, year = {2005}, abstract = {We investigated the impact of method input parameters on component performance, which is usually neglected during an application design stage. We evaluated a set of Commercial Off-The-Shelf (COTS) components which use Enterprise Java Beans (EJB) technology. These components were deployed on Web- Sphere Application Server and tested using a custom-built remote client. The client keeps track of execution times, while the server has JProbe Profiler embedded in the EJB container to monitor the interactions. For test purposes we used only stateless session beans, allowing us to concentrate on the possible dependency of server performance on input parameter variations. Test results show that significant performance impacts can be caused by a relatively small number of input parameter dependencies.}, keywords = {EJB container, COTS, method input parameters, performance, profiling}, author = {A.Oufimtsev and L.Murphy} }
@inproceedings { 438, title = {Middleware Support for Data-Flow Distribution in Web-Services Composition}, booktitle = {European Conference on Object-Oriented Programming}, year = {2005}, abstract = {Composition ofWeb services helps to lower the time-to-market of service-based applications by reusing the functionality provided by ser- vices that are already deployed at geographically distributed locations. Due to the diversity of services, the client acceptance of new applica- tions is determined more and more by non-functional aspects, such as Quality of Service, or cost. The throughput, response time, and commu- nication cost of composite services depend on the characteristics of each component service involved, as well as on the manner these components are tied together. Research has shown that distributed data-°ow models can o®er better performance and lower communication costs in service composition than centralized models. However, an impediment towards data-°ow distribution in Web services composition is that the compo- nent services cannot exchange data directly without central mediation. We propose therefore a non-intrusive approach for achieving data distri- bution among Web services that are engaged in composition, bringing minimal extensions to the underlying middleware and not tightening the coupling between them}, keywords = {QoS,Web Service}, author = {L.M.Patcas and J.Murphy and Gabriel-Miro Muntean} }
@proceedings { 387, title = {Mitigating Interference between IEEE 802.16 Systems Operating in License-exempt Mode}, year = {2005}, abstract = {A rudimentary approach to mitigate interference issues in license-exempt 802.16 systems is presented. This approach operates by permitting each Base Station (BS), and associated Subscriber Stations (SSs) to remain inactive for a speci¯ed fraction of the time. Other systems can then transmit with a reduced likelihood of interference. A simulator was developed to determine how this system performs. The results show that the throughput of the system is very sensitive to the fraction of time each BS is active; the system throughput is maximised when each BS is active less than 40% of the time for the scenarios studied. The re- sults demonstrate a discrepancy between uplink and downlink through- put which can be attributed to the greater amount of overheads in the uplink. Finally, the results show that broadcast information being trans- mitted periodically at full power has a signi¯cant detrimental impact on the system.}, keywords = {Internet,Base Station}, author = {O.Ashagi and S.Murphy and L.Murphy} }
@article { 308, title = {New Fiber Delay Line Usage Strategy in Optical Burst Switching Networks}, journal = {Networks & Communication Systems}, volume = {NCS 2005}, year = {2005}, pages = {5 Pages}, publisher = {International Association of Science and Technology for Development}, abstract = {Optical Burst Switching (OBS) is a new paradigm for future all-optical networks. In an OBS node, a Fiber Delay Line may be used to delay a burst, effectively increasing its offset time. Traditionally, FDLs were used in contention resolution, i.e. a burst was only buffered if it would otherwise been dropped. We propose a different approach, where delay lines are used also to better arrange bursts in time. In our strategy both outgoing channels and FDL channels are assigned a price, according to their suitability for a particular burst. When a control packet arrives at a core node, all the possible ways of handling the corresponding burst are found (the outgoing channel, with or without a FDL), and the one with a lowest total price is chosen. This makes it possible to use most FDL channels for the majority of the time, reducing the probability of future contention. We present simulation results, showing how node performance depends on the size of a FDL bank, using either Last Available Unused Channel with Void Filling (LAUC-VF) and the traditional FDL usage strategy or our algorithm.}, keywords = {High-speed Internet, Optical Burst Switching, Fiber Delay Lines, burst scheduling}, author = {Klusek,B. and Murphy,J. and Barry,L.P.} }
@inproceedings { 304, title = {Network Selection Decision in Wireless Heterogenous Networks}, booktitle = {IEEE 16th International Symposium on Personal.Indoor & Mobile Radio Communications}, year = {2005}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In future wireless and mobile environments it is likely that users will have access to multiple networks at the same time. Therefore there is a need to have mechanisms in place to decide which network is the most suitable for each user at each moment in time for every application that the user requires. We propose a user-centric solution where users choose the radio access network which meets their data transfer terms best. Naturally, each user wants timely quality data delivery at a low cost. In the radio environment data rates can never be guaranteed due to the unreliable nature of the radio links. The user network selection algorithm needs to predict the data rate on offer in each of the available networks and make the decision based on those predictions. This paper allows the user to select the network that will maximise the consumer surplus for non real-time data, while taking into account the delays.}, keywords = {Non real-time data, RAN Selection Decision, Service Oriented Heterogeneous Wireless Networks}, author = {Ormond,O. and Perry,P. and Murphy,J.} }
@inproceedings { 434, title = {Network Selection Strategy in Heterogenous Wireless Networks}, booktitle = {IT&T Conference }, year = {2005}, abstract = {Next generation communications will offer a wide range of services available to users anywhere at any time. How wireless users access those services depends on the current user context: location, characteristics of the available networks, user preferences, application requirements and terminal capabilities. The vision is that users will not be tied down to a long-term contract with one single operator and will instead be able to dynamically choose access provision on a per call basis. The evolving competitive marketplace will provide a choice of access networks in any given location, each offering different network technologies with varying characteristics to transport the user’s communications application. This paper highlights the need for an access network selection decision strategy to aid users operating in this heterogeneous multi-network wireless environment. We propose a consumer surplus based algorithm that selects the best available network for transferring non real-time data, with user specified time constraints. When compared to an always cheapest strategy simulation results show significant performance gains in transfer completion time for the consumer surplus based strategy.}, keywords = {Wireless Network,Communication}, author = {O.Ormond and Gabriel-Miro Muntean and J.Murphy} }
@article { 382, title = {Optium Adaptation Trajectories for Streamed Multimedia}, journal = {ACM Multimedia Systems }, volume = {10}, year = {2005}, pages = {392-401}, publisher = {ACM SIGMM}, abstract = {Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptations. We propose that an optimal adaptation trajectory through the set of possible encodings exists and that it indicates how to adapt encoding quality in response to changes in network conditions to maximize user-perceived quality. Such an optimum adaptation trajectory can be used with any transmission adaptation policy. We describe the subjective tests we carried out to find such trajectories for a number of different MPEG-4 video clips and indicate how this knowledge could be used in the operation of a practical system.}, keywords = {Perceptual video quality · Adaptive multimedia transmission · Subjective testing · Video encoding}, author = {N.Cranley and P.Perry and L.Murphy} }
@proceedings { 421, title = {Objective & Subjective Evaluation of QAOS Video Streaming over Broadband Networks}, year = {2005}, abstract = {This article presents objective and subjective testing results that assess the performance of the Quality-Oriented Adaptation Scheme (QOAS) when used for high quality multimedia streaming over local broadband IP networks. Results of objective tests using a QOAS simulation model show very efficient adaptation in terms of end-user perceived quality, loss rate, and bandwidth utilization, compared to existing adaptive streaming schemes such as LDA+, and TFRCP. Subjective tests confirm these results by showing high end-user perceived quality of the QOAS under various network conditions.}, keywords = {QOAS,IP Networks}, author = {G.Muntean and P.Perry and L.Murphy} }
@inproceedings { 302, title = {Performance Modelling of a Distributed Approach to Interference Mitigation in License-Exempt IEEE 802.16 Systems}, booktitle = {IEEE International Symposium on New Frontiers in Dynamic Spectrum Access Networks(DySPAN 2005)}, year = {2005}, publisher = {University College Dublin}, organization = {University College Dublin}, abstract = {In this paper, three approaches to modelling a distributed approach to interference mitigation in 802.16 Licenseexempt (LE) systems are described. An Interference-free (IF) approach in which no interference is permitted at any node of the system; a Controlled-interference (CI-T) and a Controlled- Interference with Fairness (CI-F) approaches where interference is permitted at nodes that do not benefit from receiving the current transmission. The results show that the CI-F and CI-T schemes result in much better overall performance that either the IF scheme or the distributed scheme. Further, they result in much greater levels of BS activity. Despite being very conservative, even the IF scheme performs better than the distributed scheme in terms of throughput. This can be attributed to the fact that the distributed scheme suffers from collisions.}, keywords = {Wireless Communication}, author = {Ashagi,O. and Ruzzelli,A.G. and Murphy,L. and Murphy,J.} }
@proceedings { 379, title = {Performance of VoIP over IEEE 802.11g DSSS-OFDM Mode with IEEE 802.11e QoS Support}, year = {2005}, address = {U.K}, abstract = {This paper examines, via simulation, the performance of an 802.11e MAC over an 802.11g PHY operating in DSSS-OFDM mode. The DSSS-OFDM scheme provides data rates of up to 54Mb/s as well as interoperability with 802.11b nodes. Due to the widespread use of 802.11b nodes, such interoperability is an important consideration. This paper involves a study of the number of simultaneous bidirectional G.711 VoIP calls that can be supported by such a WLAN. The results show that this mode of operation introduces a very significant overhead. The actual number of calls that can be carried is limited to 12 when using the 24Mb/s data rate and 13 when using either the 36Mb/s or 54Mb/s rates. These results demonstrate the well-known disparity between uplink and downlink performance, with the downlink imposing the limit on the number of calls that can be carried by the system in the cases studied. The results also show that when when a significant amount of lower priority traffic is introduced into the system, it can have a significant impact on VoIP call capacity despite the use of 802.11e.}, keywords = {WLAN, IEEE 802.11e, QoS, Voice over IP, Medium Access Control}, author = {G.Hanley and S.Murphy and L.Murphy} }
@proceedings { 381, title = {Performance Modeling & Prediction of Enterprise JavaBeans with Layered Queuing Network Templates }, year = {2005}, address = {Lisbon,Portugal}, abstract = {Component technologies, such as Enterprise Java Beans (EJB) and .NET, are used in enterprise servers with requirements for high performance and scalability. This work considers performance prediction from the design of an EJB system, based on the modular structure of an application server and the application components. It uses layered queueing models, which are naturally structured around the software components. This paper describes a framework for constructing such models, based on layered queue templates for EJBs, and for their inclusion in the server. The resulting model is calibrated and validated by comparison with an actual system.}, keywords = {Layered Queueing Network, template, Enterprise Java Bean, performance modeling, model calibration, software profiling.}, author = {J.Xu and A.Oufimtsev and M.Woodside and L.Murphy} }
@proceedings { 388, title = {Performance Comparison of Multiplexing Techniques for MPEG-4 Object Based Content}, year = {2005}, abstract = {A study of the performance of a number of different multiplexing schemes was conducted in the context of streaming of MPEG-4 object-based content, with particular emphasis on streaming content to mobile devices. The comparison involved six different schemes. The schemes differed in terms of how they packed the data for each arbitrarily shaped video object into packets. An experimental testbed was constructed to compare the performance of the different schemes. The experiments showed that the scheme in which no effort is made to maximise the amount of data in the packet performs worse than the others in terms of the amount of overhead it generates and the video quality obtained when it is used to stream content. The other schemes did exhibit small differences in terms of the amount of overhead generated and video quality obtained, but the differences were not sufficiently large to be able to identify any as being clearly better than the others.}, keywords = {MPEG-4,Multiplexing}, author = {S.Murphy and S.Goor and L.murphy} }
@article { 380, title = {Subjective Assessment of the Quality-Oriented Adaptive Scheme}, journal = {IEEE Transactions on Broadcasting}, volume = {51}, year = {2005}, pages = {276-286}, publisher = {IEEE}, abstract = {The Quality-Oriented Adaptation Scheme (QOAS) supports the distribution of high quality multimedia services to a large number of simultaneous customers via given broadband IP infrastructure. This paper presents subjective testing results that augment previously reported objective performance assessment. Clips representing different classes of multimedia sequences in terms of motion content and types were selected and streamed using a QOAS-based prototype system. Congested delivery network conditions were emulated and the effects of the consequent QOAS-driven adaptations were subjectively assessed by end-users. The test subjects have also graded their perceived quality when using a nonadaptive streaming approach. The QOAS-related results were much higher than those obtained for a nonadaptive approach, being above the “good” perceptual level for all multimedia clips and in all tested delivery conditions.}, keywords = {Adaptive multimedia streaming, end-user perceived quality, feedback control, subjective testing.}, author = {G.Muntean and P.Perry and L.Murphy} }
@inproceedings { 305, title = {Supporting Flexible Network Operator Policies in EGPRS Through Admission Control}, booktitle = {IFIP 10th International Conference on Personal Wireless Communications}, year = {2005}, publisher = {University College Dublin}, organization = {University College Dublin}, abstract = {Many of the admission control strategies for cellular data networks proposed in the literature allow the network operator to use di®erent policies, depending on the network load, the number of users from each quality of service class, etc. Each policy is applied in a certain region, the regions being separated by thresholds. Those approaches su®er from a lack of °exibility: when the operating conditions change, the values for the thresholds have to be re-calculated. Our work supports °exible and adaptable network operator policies, overcoming the drawbacks of the existing algorithms through a fuzzy logic based solution.}, keywords = {Network}, author = {Todinca,D. and Sora,I. and Perry,P. and Murphy,J.} }
@proceedings { 377, title = {Synchronisation of Internet Multimedia Streams:Some Issues & Solutions}, year = {2005}, address = {Miami,Florida}, abstract = {Synchronised clocks and circuit switching constitute a basic building block within the heart of the traditional PSTN and this coupled with dumb terminals ensures that media synchronisation is not an issue. The same cannot be said of Internet Multimedia where delays are generally non-deterministic and where terminals are much more complex. Previous work by the authors has shown that by incorporating synchronised time into VoIP terminals, significant gains in voice quality can be achieved. Related work by the authors has examined the extent to which a lack of synchronisation (or skew) both within and between terminals can affect VoIP quality and has proposed and tested a high-level solution for skew detection/compensation. In this paper we present a number of more complex scenarios where the lack of clock synchronisation can impact on performance; these include PSTN/VoIP gateways, the use of media mixers for combining media streams and conferencing services. We describe a number of testbeds currently under development where the use of synchronised time and the high level skew detection/compensation approach will be evaluated as a means of dealing effectively with these scenarios.}, keywords = {Media Synchronisation, Clock Skew, PSTN-VoIP Gateway, Media Mixers .}, author = {H.Melvin and L.Murphy} }
@proceedings { 385, title = {Solution Design for Efficient Distribution of Muktimedia-based Services to Home Residences}, year = {2005}, publisher = {Performance Engineering Lab}, abstract = {This paper presents a design problem and its solution in form of the Quality Oriented Adaptation Scheme (QOAS), the client-server system that implements it and the related architecture for the delivery of multimedia-based services to residential users. QOAS was proposed to adaptively stream high quality multimedia-based services to home residences, adjusting the content based on existing delivery conditions. QOAS principle, the system that deploys it and the architecture of the system for the delivery of multimedia-based services are briefly described. Subjective testing results are also presented and show very good performance of the implemented QOAS-based multimedia delivery system.}, keywords = {Software Development, Multimedia Streaming, Subjective Testing}, author = {G.Muntean and L.Murphy} }
@proceedings { 390, title = {Seamless Handover of Streamed Video over UDP between Wireless LAN's}, year = {2005}, abstract = {The seamless handover of streamed video in a WLAN with UDP as the transport layer is considered. The use of handover for stationary nodes in the case of network congestion is motivated. Next, the relationship between delay and loss in WLANs is studied, with the conclusion that delay can be used as an indicator of when loss is likely to occur. Delay can therefore be used as a basis of a handover scheme which can minimize loss. Such a handover scheme is proposed in which the client makes two simultaneous connections to the same server through two separate WLANs, and it is shown that the client can use the relative packet delay between the two streams to determine which network delivers the best performance; this information is then used to determine when to perform a handover. The proposed scheme is implemented and results are presented that show the successful handover of an RTP over UDP stream using this scheme in a live WLAN environment.}, keywords = {Seamless Handover, Streamed Video, Wireless LAN.}, author = {G.Cunningham and S.Murphy and L.Murphy and P.Perry} }
@article { 375, title = {A New Adaptive Multimedia Streaming System for ALL-IP Multi Service Networks}, journal = {IEEE Transactions on Broadcasting}, volume = {50}, year = {2004}, pages = {1-10}, publisher = {IEEE}, abstract = {A significant challenge in all-IP multi-service networks is to balance the goal of providing high-quality services to the end-users with the desire to maximize the number of end-users that can be simultaneously served. This paper presents a solution to this challenge by using the Quality-Oriented Adaptation Scheme (QOAS) for delivering multimedia streams. This adaptive mechanism uses feedback from clients regarding the quality of delivery to assist the server in making dynamic adjustments to the transmitted streams. Experimental objective and subjective test results illustrate the significant performance improvements achieved by QOAS, both in terms of number of simultaneous viewers served and of end-user perceived quality.}, keywords = {Adaptive multimedia streaming, all-IP multi-service networks, dynamic feedback, grading scheme, statistical multiplexing.}, author = {G.Muntean and P.Perry and L.Murphy} }
@inproceedings { 288, title = {An Analysis of Delay of Small IP Packets in Celluar Data Networks}, booktitle = {IEE 5th International Conference on 3G Mobile Communication Technologies}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The delay characteristics of small IP packets in cellular data networks is investigated through the analysis of the SR-ARQ mechanism. The delay of the radio link controller is taken as the primary delay in the radio access network and all core networking delays are neglected. Results indicate that the average delay may be a misleading measure of system performance for conversational traf�c such as Voice over IP packets.}, keywords = {3G Mobile Communication}, author = {Graja,H. and Peery,P. and Murphy ,J. } }
@inproceedings { 290, title = {A Statistical Analysis of IP Packet Delay and Jitter in Cellular Networks}, booktitle = {IEEE 15th International Symposium on Personal,Indoor & Mobile Radio Communications}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A novel methodology is proposed for the analysis of the IP packet delay performance of SR-ARQ mechanisms in a generalized wireless system. A simulation model of the system including a novel channel model is described and results are obtained for a range of IP packet size. To demonstrated the ef�cacy of the methodology, the test scenario is tailored to the transmission of small packets containing real-time data carried over an EGPRS system. The results show that the use of a mean value for IP packet delay estimation is of limited use when small packets are considered.}, keywords = {ARQ, IP packet delay, wireless QoS, mobile multimedia}, author = {Graja,H and Perry,P. and Murphy J } }
@inproceedings { 291, title = {Adaptive Dynamic Bandwidth Allocation Algorithm for Ethernet PONs}, booktitle = {30th European Conference on Optical Communications,ECOS 2004}, number = {740-741}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {We present an Adaptive Dynamic Bandwidth Allocation algorithm for Passive Optical Networks. We include results of simulation experiments to show the comparison of its performance with other bandwidth allocation algorithms.}, keywords = {Optical Communication}, author = {Nowak,D. and Perry,P. and Murphy,J.} }
@inproceedings { 292, title = {A Novel Service Level Agreement Based Algorithm for Diffrentiated Services enabled Ethernet PONs}, booktitle = {9th Opto Electronics & Communications Conference & 3rd International Conference on Optical Internet}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {We present a Dynamic Bandwidth Allocation algorithm that supports Service Level Agreements in Ethernet Passive Optical Networks and show that it provides a reliable protection of agreed traffic parameters. We include results of simulation experiments.}, keywords = {Optical Communication}, author = {Nowak,D. and Perry,P. and Murphy,J.} }
@inproceedings { 294, title = {A Framework for automatically Detecting & Assesing Performance Antipatterns in Component Based Systems using Run -Time Analysis}, booktitle = {9th International Workshop on Component Oriented Programming(WCOP) & 18th European Conference on Object Oriented Programming(ECOOP)}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {We propose a framework for automatically detecting and assessing the impact of poor performance design (performance antipatterns) in component based systems using run time analysis. The framework consists of three modules, a monitoring module, a detection module, and a visualization module. Our framework borrows techniques from the field of Knowledge Discovery in Databases. We intend to instantiate the framework for the Enterprise Java Beans platform.}, keywords = {Component Oriented}, author = {Parsons,T. and Murphy,J.} }
@inproceedings { 295, title = {Automatic Performance Management in Component Based Software Systems}, booktitle = {IEEE International Conference on Autonomic Computing}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A framework for automatic performance tuning of component-based enterprise applications is presented. A non-intrusive monitoring and diagnosis module is employed by an application adaptation module that automatically chooses optimal component implementations for different execution contexts. Both modules can optimize their overhead by automatically focusing on the application hot-spots, making the framework suitable for long-running systems. Currently, implementation work is targeted at J2EE systems}, keywords = {IEEE}, author = {Diaconescu,A. and Mos,A. and Murphy,J.} }
@inproceedings { 298, title = {A Framework for Automatic Performance Monitoring,Analysis & Optimisation of Component based Software Systems }, booktitle = {2nd ICSE Workshop on Remote Analysis and Measurement of Software Systems(RAMSS 04),26th International Conference on Software Engineering(ICSE 2004)}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A framework for automating the runtime performance management of component-based software systems is presented. The framework leverages static performance information obtained at component development time, if available, and executes performance monitoring, analysis and optimisation operations during runtime. The dynamic performance optimisation process is based on the automatic selection and activation of one of multiple functionally-equivalent implementation variants, available at runtime, each one optimised for a different running context. The framework consists of three main modules: monitoring & diagnosis, evaluation & decision and component activation. Current implementation work targets Enterprise JavaBeans systems.}, keywords = {Component Oriented`}, author = {Diaconescu,A. and Murphy,J.} }
@proceedings { 369, title = {Application Layer Delay-Centric Handover of Streamed Video in a 4G Network}, year = {2004}, publisher = {Performance Engineering Lab}, address = {Limerick,Ireland}, abstract = {In the currently proposed schemes for performing a vertical handover between wireless networks, it is common for a substantial break in connectivity to occur that would be unacceptable for streamed video. This paper proposes a scheme that ensures packets are not lost, through the use of soft handover. It is shown that the client can decide when to perform a soft handover by using the difference in packet delay between the two streams. The scheme is implemented and results are presented that show the successful handover of an RTP stream using this scheme in a test bed that emulates network conditions.}, keywords = {Wireless Network,4G}, author = {G.Cunningham and P.Perry and L.Murphy} }
@proceedings { 374, title = {An Evaluation of Delay-Aware Receiver Playout Strategies for VoIP Applications}, year = {2004}, address = {Athens,Greece}, abstract = {Previous work by the authors confirm the feasiblity of implementing a delay-aware receiver buffering strategy based on synchronised time within VoIP applications.Our objective in this paper is to extensively test this delay-aware approach, termed the hybrid playout strategy over diverse networks using a combination of simulation & delay emulation.We utilise both measured delay data & derived delay models and quantify the significant performance gainsthrough use of the ITU-TE model.We also analyse recent Internet delay studied to further assess the hybrid's wider applicably.}, keywords = {Periodicd Network Measurements,Simulation,Network Emulation,Synchronised Time}, author = {H.Melvin and L.Murphy} }
@proceedings { 376, title = {A New VoIP Adaptive Playout Algorithm }, year = {2004}, address = {London,UK}, abstract = {A novel playout algorithm for VoIP applications is presented. The playout times of voice packets are calculated using adaptive estimation of network delays. In contrast to previous solutions, the weighting factor that controls the estimation process is dynamically adjusted according to the observed delay variations. This results in higher-quality estimates of network delays. With this algorithm, the trade-off between buffering delay and late packet loss at the receiver is significantly improved. Experimental results show that the new algorithm can achieve higher subjective call quality than the basic adaptive algorithm, as measured by the ITU-T EModel methodology.}, keywords = {jitter compensation, playout buffer algorithm}, author = {M.Narbutt and L.Murphy} }
@article { 285, title = {BER Performance in Wavelength Packet Switched WDM systems during Nano-Second Wavelength switching Events}, journal = {Journal of Optical Communication}, volume = {242}, year = {2004}, pages = {171-177(7Pages)}, publisher = {Research Institute for Network and Communications Engineering}, abstract = {An important characteristic of wavelength tuneable laser transmitters is that as they tune between output wavelength channels they may generate light at a range of other wavelengths. This effect may ultimately influence the design of WDM wavelength packetswitched networks employing wavelength tuneable transmitters. We have investigated this effect by examining the BER transmission performance of a WDM channel as a function of the degree of attenuation of another WDM wavelength signal during fast wavelength switching events. Our results show the importance of attenuating the output signal from the wavelength switched laser in order to prevent performance degradations on the monitored data channel.}, keywords = {Optical communications, networks, wavelength division multiplexing, tuneable laser, packet switching, cross-channel interference}, author = {Dantcha,A. and Barry,L. and Murphy J. and Dunne,J. and Mullane,T. and Mcdonald,D.} }
@inproceedings { 286, title = {Bandwidth Allocation For Service Level Agreement Aware Ethernet Passive Optical Networks}, booktitle = {IEEE Globecom 2004}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Passive Optical Networks (PON) are thought to be the next step in the development of access networks and providing broadband access in the ”last mile” area. Ethernet PONs (EPONs) are gaining the most attention from industry as they offer a highly flexible, cost effective solution. In this paper, we present a new approach to the problem of optimal bandwidth allocation in EPONs. We show that by moving all the access control functionality to the Optical Line Terminator, a flexible solution could be achieved which offers full support for Service Level Agreements and removes the burden of managing the configuration of every Optical Network Unit. We include results of simulations that show that such an approach can deliver good performance in terms of average and maximum packet delay. We show that, a novel Grant Multiplexing scheme can significantly reduce jitter and end-to-end delay experienced by the high priority classes of traffic. To prove these points we present results of detailed experiments that were run on a C++ event driven simulator, that we haveloped.}, keywords = {IEEE}, author = {Nowak,D. and Perry,P. and Murphy,J.} }
@inproceedings { 293, title = {Bandwidth Scheduling Techniques For Diffrentiated Services Support in Ethernet Passive Optical Networks}, booktitle = {4th International Symposium on Communication Systems,Networks & Digital Signal Processing}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Passive Optical Networks are thought to be the next step in the development of Access Networks and providing broadband access in the ”last mile” area. Ethernet PONs (EPON) gain the most attention from the industry as they offer highly flexible, cost effective solution. In this paper we propose algorithms that provide Dynamic Bandwidth Allocation and shift the burden of queue management from the customer to the network, this results in less complicated and more generic equipment used on the customer’s premises. We show the results of simulations to validate the effectiveness of algorithms presented. }, keywords = {Optical Communication}, author = {Nowak,D. and Perry,P. and Murphy,J.} }
@inproceedings { 287, title = {Client Controlled Network Selection}, booktitle = {IEE 5th International Conference on 3G Mobile Communication Technologies(3G 2004)}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {It is likely that an ensemble of overlapping heterogeneous wireless networks will be required to provide ubiquitous data communications. In this scenario, the mobile user’s choice of network will directly affect the applications’ performance. This paper examines this decision, and proposes that it is made by the client application by considering network characteristics and cost. This is facilitated by a modified version of SCTP. Using simulation results, we show that a marked improvement in application performance is possible by monitoring the available networks, and making the appropriate selection.}, keywords = {SCTP, path selection, mobility management}, author = {Noonan,J. and Perry,P. and Murphy,J.} }
@inproceedings { 299, title = {COMPAS:Adaptive Performance Monitoring of Component Based Systems}, booktitle = {2nd ICSE Workshop on Remote Analysis and Measurement of Software Systems(RAMSS 04),26th International Conference on Software Engineering(ICSE 2004)}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A performance monitoring framework for adaptive instrumentation and diagnosis is presented. Instrumentation is performed by low-overhead monitoring probes which are automatically activated and deactivated based on runtime conditions. Both a collaborative distributed model and a centralised model for assisting the diagnosis and adaptation processes are presented. The framework targets component-based systems in general and J2EE in particular.}, keywords = {Component Oriented`}, author = {Mos,A. and Murphy,J.} }
@inproceedings { 423, title = {Content-Based Adaptation of Streamed Multimedia}, booktitle = {7th IFIP/IEEE international Conference on Management of Multimedia Networks & Services}, year = {2004}, abstract = {Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptations. We show that an Optimal Adaptation Trajectory (OAT) through the set of possible encodings exists, and that it indicates how to adapt encoding quality in response to changes in network conditions in order to maximize user-perceived quality. The OAT is related to the characteristics of the content, in terms of spatial and temporal complexity. We describe an objective method to automatically determine the OAT in response to the time-varying characteristics of the content. The OAT can be used with any transmission adaptation policy. We demonstrate content-based adaptation using the OAT in a practical system, and show how this form of adaptation can result in differing adaptation behaviour.}, keywords = {OAT,Streamed Multimedia}, author = {N.Cranley and P.Perry and L.Murphy} }
@inproceedings { 450, title = {Delay-Centric Handover in SCTP over WLAN}, booktitle = {Trans. on Automatic Control & Control Science}, year = {2004}, abstract = {In the field of personal mobile communications, it has been suggested that SCTP could provide a solution to the problems encountered by the currently implemented TCP/Mobile IP scheme. By exploiting SCTP’s multihoming feature to connect to several separate wireless networks concurrently, allows a Mobile Node to choose which wireless path suits the particular needs of the user application it is running. However, there is one drawback to this scenario - the current handover scheme implemented in SCTP is failure-centric in nature. This paper proposes an improved handover scheme for SCTP. This proposed scheme offers the benefit of performing handover based on measured path delays, thus it does not require a path failure for handover to occur. In some cases it can actually pre-empt the path failure, and handover before it occurs.}, keywords = {SCTP, Handover, WLAN, Computer}, author = {A.Kelly and Gabriel-Miro Muntean and P.Perry and J.Murphy} }
@inproceedings { 464, title = {Evaluating the Impact of Network Performance on Video Streaming Quality for Categorised Video Content}, booktitle = {14th International Packet Video Workshop}, year = {2004}, abstract = {This paper describes an empirical study that examines the relationship between network performance and video streaming quality for different types of video content. Three classes of video content – newsclips, music and movie trailers – are studied in order to generate appropriate maps from network performance to a quality score with correlates with perceived video quality. More specifically, a mapping from measured packet loss and delay jitter to one of a number of levels of approximate video quality is obtained. This mapping information can be used in the context of dynamic server selection to provide QoS support to a distributed RTP-based multimedia delivery system. The focus of the study is on short clips of low bit-rate video which is suitable for transmission to mobile devices. The results illustrate that the three classes of content react quite differently to changes in the network conditions. The movie trailers, which are typically characterized by high motion content suffer considerably more than the other two categories when there is jitter or loss on the network path between client and server. The music video content behaves similar to the high motion content for low packet loss and jitter, but tends to behave more like the low motion news content in the presence of high loss and jitter. There is sufficient difference between the performance of the different video content classes to warrant different maps for each of the content types which can be used to support server selection decisions in a distributed video content system.}, keywords = {Video quality assessment, Real-time video, Video streaming, QoS support, Server selection, Distributed multimedia}, author = {S.Murphy and M.Searles and C.Rambeau and L.Murphy} }
@proceedings { 368, title = {Experimental Performance Analysis of RTP-based Transmission Techniques for MPEG-4}, year = {2004}, publisher = {Performance Engineering Lab}, address = {Irvine,California}, abstract = {The performance of different approaches to streaming MPEG-4 video over RTP was investigated. Three specific approaches were compared: first, no multiplexing is used and only a single video data unit i.e. a coded video frame or a coded video frame segment, is transmitted per packet; in the second many video data units are multiplexed into a single RTP packet. The third approach is similar to the multiplexed case, but the units are interleaved across RTP packets. An experimental test bed was developed to determine the performance of the schemes under various emulated network conditions. The streaming approaches were analysed in terms of transmission performance and streamed video quality. The performance of the two multiplexed approaches was very similar, with neither showing a clear advantage over the other; both multiplexed cases performed better than the nonmultiplexed cases. When multiplexing was employed there was a 60% reduction in the number of packets required to stream the content, and the overhead introduced by packet headers was reduced from approximately 8% to just over 4%. In terms of video quality, the multiplexed cases resulted in roughly 5% fewer damaged frames.}, keywords = {Video Streaming, MPEG-4, Multiplexing, FlexMux, RFC 3016.}, author = {S.Goor and S.Murphy and L.Murphy} }
@proceedings { 432, title = {End-User Quality of Experience Layer for Adaptive Hypermedia Systems}, year = {2004}, abstract = {In the context of new devices and the variety of network technologies that allow access to the Internet, the deployers of Web applications need to ensure that end-users have a positive experience using new applications and they will be willing to re-use them. User experience is dependent not only on the content served to them, but also on the performance of that service. This paper explores a new dimension of individual differences between Web users: end-user Quality of Experience (QoE). It proposes a solution on how to provide satisfactory end-user QoE in the field of educational adaptive hypermedia. A new QoE layer for Adaptive Hypermedia is introduced that attempts to take into account multiple factors affecting Quality of Experience, which might arise from a wide range of Web components (e.g. text, images, video, audio). Usability evaluation based on comparison of a classic adaptive e-learning system with a QoE-aware one has shown that students considered the QoE-aware system significantly more usable than the classic system. Learning performance tests indicated that the changes made by the QoE-aware system did not affect the learning capabilities offered by the classic system.}, keywords = {Internet,QoE}, author = {Muntean,C.H. and McManis,J.} }
@inproceedings { 422, title = {Issues in Developing a Simulation Model of an EJB Application Server}, booktitle = {Computer Measurement Group 2004 International Conference}, year = {2004}, abstract = {Despite the fact that EJB (Enterprise Java Beans) is such a widely used technology, research in the area of performance modelling EJB application servers is quite sparse. This paper will describe how Ptolemy II, a discrete event simulator and general modelling tool, can be used to build a scalable model of an EJB system that allows users to input variables that describe interactions and their constituent methods, as well as system parameters. The model will output the average time for each given user interaction and allow users to seek system improvements by changing the system parameters and workloads.}, keywords = {EJB,Ptolemy,}, author = {D.McGuinness and L.Murphy and A.Lee} }
@inproceedings { 289, title = {Novel Admission Control Algorithm for GPRS/EGPRS Based on Fuzzy Logic}, booktitle = {IEE 5th International Conference on 3G Mobile Communication Technologies}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {As users in a GPRS/EGPRS network have different Quality of Service (QoS) demands, the network aims to satisfy their demands while maximizing the utilization of the existing resources. A crucial aspect of the resource allocation problem in cellular data networks is the admission control (AC). We propose a new session admission control algorithm that overcomes most of the difficulties encountered by the existing AC algorithms. The novelty of our approach is the use of fuzzy logic (fuzzy inference) for the AC. We demonstrate the efficiency of our AC algorithm by simulations.}, keywords = {GPRS/EGPRS, admission control, fuzzy logic}, author = {Todinca,D. and Perry,P. and Graja,H. and Murphy,J.} }
@article { 372, title = {Performance Comparison of Local Area Video Streaming Systems}, journal = {IEEE Communications Letters}, volume = {8}, year = {2004}, pages = {326-328}, publisher = {IEEE}, abstract = {The performance of our Quality Oriented Adaptation Scheme (QOAS) for multimedia streaming in local networks is compared with other existing solutions (TFRCP, LDA+, and non-adaptive). This comparison is done in terms of bandwidth utilization, number of concurrent clients, loss rate, and end-user perceived quality. Simulation results show that for the same average end-user quality, our QOAS system can accommodate a significantly higher number of simultaneous clients while also having higher bandwidth utilization. For the same number of clients, the average end-user quality is always higher for QOAS than for the other solutions studied.}, keywords = {Adaptive video streaming, feedback control, grading scheme, end-user quality.}, author = {G.Muntean and P.Perry and L.Murphy} }
@inproceedings { 424, title = {Performance Assesment of the Quality-Oriented Adaptation Scheme}, booktitle = {7th IFIP/IEEE International Conference on Management of Multimedia Networks & Services}, year = {2004}, abstract = {This paper focuses on the experimental performance assessment of the Quality-Oriented Adaptation Scheme (QOAS) when used for streaming high quality multimedia-based services via local broadband IP networks. Results of objective tests using a QOAS simulation model show very efficient adaptation in terms of end-user perceived quality, loss rate, and bandwidth utilization, compared to existing adaptive streaming schemes such as LDA+ and TFRCP. Subjective tests confirm these results by showing high end-user perceived quality of the QOAS under various network conditions.}, keywords = {QOAS,Bandwidth Utilisation}, author = {G.Muntean and P.Perry and L.Murphy} }
@proceedings { 371, title = {Perceptual Quality Adaptation(PQA) Algorithm for 3GP & Multi-Tracked MPEG-4Content over Wireless IP Networks}, year = {2004}, abstract = {Many adaptive delivery mechanisms have been devised for streaming multimedia over best-effort IP networks, such as the Internet. Most of these adaptive schemes do not consider the user’s perception of quality when making adaptations. We describe a Perceptual Quality Adaptation algorithm (PQA) and prototype system architecture that uses knowledge of user perceived quality to make adaptation decisions using an optimum adaptation trajectory. This optimum adaptation trajectory indicates how encoding quality should be adapted (upgraded/downgraded) with respect to user perceived quality in response to rapidly fluctuating network conditions. We present simulation results that demonstrate the behavior of a perceptual quality adaptation algorithm.}, keywords = {Quality, Perception, Multimedia, Adaptation algorithm, MPEG-4, 3GP}, author = {N.Cranley and P.Perry and L.Murphy} }
@proceedings { 373, title = {Quality-Oriented Adaptation Scheme (QOAS) for High Bit-Rate Multimedia Streaming}, year = {2004}, abstract = {A Quality Oriented Adaptation Scheme (QOAS) for multimedia streaming in local networks is introduced, and its performance is compared with other existing solutions (TFRCP, LDA+, and non-adaptive). QOAS is designed to balance two opposing goals: providing the highest quality to the end-users, while increasing the network operators’ revenues by increasing the number of simultaneous customers. Simulation results show that for the same average end-user quality, our QOAS system can accommodate a significantly higher number of simultaneous clients while also having higher bandwidth utilization. For the same number of clients, the average end-user quality is always higher for QOAS than for the other solutions studied.}, keywords = {Adaptive video streaming, multimedia networking, feedback control, end-user perceived quality.}, author = {G.Muntean and P.Perry and L.Murphy} }
@proceedings { 433, title = {QoSAHA:A Performance Oriented Learning System}, year = {2004}, abstract = {This paper presents a framework for QoS enhancement of Adaptive Hypermedia Systems which is applicable to the area of education. The enhanced system adapts Web content based on both user-perceived QoS and user knowledge. The goal of the enhancement is to be able to improve performance metrics while not significantly affecting learning outcomes. A novel Perceived Performance Model that captures user-perceived performance and suggests content constraints to improve user satisfaction is described. The approach is tested by comparing the AHA! System to a QoS enhanced version of the same system. Preliminary results show that the enhancement significantly improves download times for users with low speed connections, while maintaining similar learning outcomes}, keywords = {QoS}, author = {Muntean,C.H. and McManis,J.} }
@inproceedings { 296, title = {Simulation of Multimedia Traffic over SCTP Modified for Delay-Centric Handover}, booktitle = {5th World Wireless Congress(B3G)}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The mobile wireless environment can be challenging for multimedia applications, with poor performance and handover issues causing service degradation. In this paper, a modified version of the new IETF transport protocol, SCTP, is shown to improve the performance of a voice-like application in an environment where two wireless LANs overlap. It does this by monitoring both networks and selecting the network with the better performance. This paper shows simulations of an SCTP handover scheme which selects the better path based on a moving average of end-to-end delay. The significant contribution of this work is to show the feasibility of a mobile transport protocol, based on SCTP, that can handover between networks and support multi-media type traffic.}, keywords = {SCTP, transport layer, handover, mobile, delay}, author = {Noonan,J. and Kelly,A. and Perry,P. and Murphy,S. and Murphy,J.} }
@proceedings { 370, title = {Soft,Vertical Hadover of Streamed Video}, year = {2004}, publisher = {Performance Engineering Lab}, address = {London,England}, abstract = {The delay and jitter of an RTP stream transported by TCP over WLAN are examined as candidates for assisting handover between networks. Jitter was found to be a good indicator of when a mobile is close to the edge of a WLAN cell and was used to spawn a vertical handover mechanism. The implemented handover scheme used an averaged delay difference to complete the handover of the video stream.}, keywords = {Handover, Streamed Video, Wireless LAN.}, author = {G.Cunningham and P.Perry and L.Murphy} }
@inproceedings { 297, title = {Using Runtime Information for Adapting Enterprise Java Beans Application Servers}, booktitle = {2nd Internatioanl Workshop on Dynamic Analysis(WODA)}, number = {52-59}, year = {2004}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Modern component-based technologies, such as Enterprise Java Beans (EJB), simplify system development by allowing developers focus on business logic, while system services are provided by an underlying application server. A class of system services, such as transactions or security, control the context in which components run. The provisioning of such services can introduce performance overhead, as some system services might be executed redundantly. As EJB components bind dynamically, the determination that such an execution is redundant can be made only at runtime. We present a runtime mechanism for identifying and removing such redundant executions.}, keywords = {Dynamic Analysis}, author = {Trofin,M. and Murphy,J.} }
@inproceedings { 281, title = {A Modified SCTP Handover Scheme for Real Time Traffic}, booktitle = {First International Working Conference on Performance Modelling and Evaluation of Heterogenous Networks}, year = {2003}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A new transport protocol, SCTP, offers the possibility of enabling mobile data communications systems to automatically handover between networks. The existing protocol implementations do this on the basis of link failure and are shown here to take of the order of fifteen seconds to perform this handover. For real time applications this is clearly unacceptable. A modified handover regime is proposed which monitors round trip time and initiates a handover when a predetermined threshold is breached. This promises to preempt link failure and has the potential to deliver Quality of Service improvements for real time users. This proposed scheme requires no alteration to the existing SCTP standard}, keywords = {Real Time Traffic}, author = {Kelly,A. and Perry,P. and Murphy J} }
@inproceedings { 282, title = {A Self Optimizing Container Design for Enterprise Java Beans Applications}, booktitle = {8th International Workshop on Component Oriented Programming}, year = {2003}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Contextual component frameworks, such as Enterprise Java Beans (EJB), facilitate the development of easily evolvable and modifiable enterprise applications. Support for dynamic re-composition, such as instance-level contextual composition and runtime binding are the base upon which such features are offered. Applications can be built out of third-party components and deployed on third-party platforms. At the same time, this black box nature of third-party components and platforms diminishes the effectiveness of traditional performance analysis methods. This raises the role played by runtime optimizations in addressing performance issues of such systems. We propose a self-optimizing application server design. The optimization is driven by the discovery of inter-component communication patterns and the application of container refactorings.}, keywords = {Component Oriented}, author = {Trofin,M. and Murphy,J.} }
@inproceedings { 284, title = {A Framework for Using Component Redundancy for Self Optimising & Self Healing Component Based Systems}, booktitle = {International Conference on Software Engineering}, year = {2003}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The ever-increasing complexity of software systems makes it progressively more difficult to provide dependability guarantees for such systems, especially when they are deployed in unpredictably changing environments. The Component Based Software Development initiative addresses many of the complexity related difficulties, but consequently introduces new challenges. These are related to the lack of component intrinsic information that system integrators face at system integration time, as well as the lack of information on the component running-context that component providers face at component development time. We propose an addition to existing component models, for enabling new capabilities such as adaptability, performance optimisation and tolerance to context-driven faults. The concept of ‘component redundancy’ is at the core of our approach, implying alternate utilisation of functionally equivalent component implementations, for meeting application-specific dependability goals. A framework for implementing component redundancy in component-based applications is described and an example scenario showing the utility of our work is given.}, keywords = {Software Architectures}, author = {Diaconescu,A. and Murphy,J.} }
@inproceedings { 361, title = {An Integrated NTP-RTCP Solution to Audio Skwe Detection & Compensation for VoIP Applications}, booktitle = {International Conference on Multimedia & Expo}, year = {2003}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The circuit switched POTS (Plain Old Telephone System) preserves the timing relationship between media samples from sender to receiver through use of a common clock. For PC-based Internet multimedia, the existence of separate audio and system clocks on either end-host can introduce significant complications. Much work has taken place in recent years that addresses the issue of system clock skew and its effect on precise delay measurement. In a Voice over IP (VoIP) environment, where adaptive buffering techniques are employed, system and audio clock skew can distort both delay measurement and playout control as well as lead to poor buffer performance. This paper presents a high level mechanism to measure and compensate for the skew relationships between system and audio clocks at each end of a multimedia session. The mechanism utilises both the Network Time Protocol (NTP) and the RTP (Realtime Transport Protocol) Control Protocol or RTCP. Preliminary and positive results are presented from a testbed system and plans for further work are outlined.}, keywords = {VoIP,Multimedia,Internet}, author = {H.Melvin and L.Murphy} }
@inproceedings { 365, title = {An Adaptive MPEG-4 Streaming System based on Object Prioritisation}, booktitle = {IEI/IEEE Symposium on Telecommunications System Research}, year = {2003}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Streaming of video and multimedia content has generated a lot of interest, especially with the recent development of mobile devices with multimedia capabilities. However, ubiquitous multimedia systems face many challenges, such as varied and limited network performance and viewing device capabilities. Adaptive streaming systems are frequently used to reconcile these limitations, while also providing an acceptable level of perceptible quality to the end user. In this paper, we propose an adaptive streaming system that exploits the Video Object (VO) coding capabilities of MPEG-4 by applying priorities to the individual objects. By allowing the content provider to define prioritisation of objects, video adaptation can be customised based on the content.}, keywords = {Video Streaming, Scalability, MPEG-4, Video Objects, Prioritisation.}, author = {S.Goor and L.Murphy} }
@proceedings { 359, title = {A Methodology for Predicting the Performance of Component Based Applications}, year = {2003}, publisher = {Performance Engineering Lab}, address = {Darmstadt,Germany}, abstract = {One of the major problems in building large-scale enterprise applications is predicting the performance of the eventual solution before the application has been built. Middleware offered by component technologies such as Sun’s Enterprise JavaBeans, Microsoft’s .NET, or OMG’s CORBA Component Model does not guarantee the fulfillment of performance requirements. These technologies support assembly of components and provide means to connect components together, but they do not provide support for predicting the quality of the assembly or an application built on assemblies. When systems are built using assemblies, an important characteristic in predicting the performance of the system is to predict the performance of a given assembly. We propose a methodology for reasoning about the performance of component based applications. Our methodology is based on creating performance profiles for each component, assembly and connection type, and groups them together in order to predict the performance of the applications. Development of a framework to implement this methodology is in progress, with the current focus on Microsoft .Net technology.}, keywords = {.Net assembly, COM+, performance prediction}, author = {N.Dumitrascu and S.Murphy and L.Murphy} }
@proceedings { 362, title = {An Adaptive MPEG-4 Streaming System based on Object Prioritisation}, year = {2003}, publisher = {Performance Engineering Lab}, address = {Limerick,Ireland}, abstract = {Streaming of video and multimedia content has generated a lot of interest, especially with the recent development of mobile devices with multimedia capabilities. However, ubiquitous multimedia systems face many challenges, such as varied and limited network performance and viewing device capabilities. Adaptive streaming systems are frequently used to reconcile these limitations, while also providing an acceptable level of perceptible quality to the end user. In this paper, we propose an adaptive streaming system that exploits the Video Object (VO) coding capabilities of MPEG-4 by applying priorities to the individual objects. By allowing the content provider to define prioritisation of objects, video adaptation can be customised based on the content.}, keywords = {Video Streaming, Scalability, MPEG-4, Video Objects, Prioritisation}, author = {S.Goor and L.Murphy} }
@proceedings { 364, title = {An Evaluation of the Potential of Synchronised Time to improve VoIP Quality}, year = {2003}, publisher = {Performance Engineering Lab}, address = {Anchorage,Alaska}, abstract = {Delivering PSTN-like quality over current besteffort Internet infrastructure presents many technical challenges. Much research in recent years has focused on receiver-based approaches which adapt to varying network conditions in order to optimize playout quality. In this paper, we propose and evaluate a receiver-based approach that implements a hybrid adaptivefixed playout regime by integrating synchronized time into the playout algorithm. Such an approach can deliver significantly better quality than existing adaptive techniques particularly when the underlying network is not heavily congested and end-toend delays are not excessive. We present some initial results from our testbed system using the ITU-T E-model to quantify improvements.}, keywords = {Internet,PSTN}, author = {H.Melvin and L.Murphy} }
@proceedings { 367, title = {Adaptive MPEG-4 transmission at the Wireless Transmitter}, year = {2003}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Streaming of video and multimedia content has generated a lot of interest, especially with the recent development of mobile devices with multimedia capabilities. However, ubiquitous multimedia systems face many challenges, such as varied and limited network performance and viewing device capabilities. Adaptive streaming systems are frequently used to reconcile these limitations, while also providing an acceptable level of perceptible quality to the end user. In this paper, we propose an adaptive streaming system that exploits the Video Object (VO) coding capabilities of MPEG-4 by applying priorities to the individual objects. By allowing the content provider to define prioritisation of objects, video adaptation can be customised based on the content.}, keywords = {Video Streaming, Scalability, MPEG-4, Video Objects, Prioritisation.}, author = {G.Cunningham and L.Murphy} }
@inproceedings { 280, title = {BER Performance in Wavelength Packet Switched WDM systems during Nano-Second Wavelength switching Events}, booktitle = {29th European Conference on Optical Communications}, year = {2003}, publisher = {Intune Technologies Ltd}, organization = {Intune Technologies Ltd}, abstract = {The BER performance of a WDM channel is investigated as a function of the attenuation of another WDM signal during fast wavelength switching events. A nano-second tuneable laser is switched across the monitored channel to perform the study.}, keywords = {Wavelength}, author = {Dantcha,A. and Barry,L. and Murphy J. and Dunne,J. and Mullane,T. and Mcdonald,D.} }
@inproceedings { 283, title = {Novel GPRS Simulator for Testing MAC Protocols}, booktitle = {IEE 4th International Conference on 3G Mobile Communication Technologies}, year = {2003}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {A simple, effective model of a GPRS/GSM cell is developed that can give a clear insight into the behaviour of MAC layer scheduling algorithms for a definable cohort of users. Users are defined in terms of their QoS class, their mobility characteristics and their traffic characteristics. The channel model is a C/I statistical model that has a variable mean value that is generated from a two state Markov model for each user. As an example, a weighted round robin scheduling algorithm is analysed within this simulated environment to predict its effect on traffic flow and user perceived network performance. Results presented show that the scheduling algorithm can simply and effectively implement QoS differentiation and reduce the perceived delay for real time streaming users, thereby improving the user perceived performance of the network.}, keywords = {3G Mobile Communication}, author = {Graja,H. and Perry,P. and Todinca,D. and Murphy ,J. } }
@proceedings { 360, title = {Probe based Dynamic Server Selection for Multimedia QoS}, year = {2003}, publisher = {Performance Engineering Lab}, address = {Ilkley,England}, abstract = {This paper proposes a probe-based scheme to select which one of a number of replica servers to use to satisfy client requests for multimedia content. Our scheme attempts to select the candidate server that can provide the best connection in terms of loss, delay and jitter (delay variation). A grading system applies meaningful values to periodic active probe measurements, and a selection algorithm chooses a server so as to avoid congested paths and bursty network traffic in order to improve end-user video presentation quality. Our proposed dynamic server selection system has been designed to work as a complementary technology with any existing multimedia congestion control system. Some experiments to evaluate the performance of the proposed scheme are described.}, keywords = {Mobile Multimedia, Multimedia QoS support, Dynamic server selection, Multimedia traffic management, Video streaming.}, author = {M.Searles and P.Perry and L.Murphy} }
@article { 357, title = {Quality Oriented Adaptation Scheme for Video-On-Demand}, journal = {IEE Electronic Letters}, volume = {39}, year = {2003}, pages = {1689-1690}, publisher = {IEE}, abstract = {The QOAS system proposed in [1, 2] is used for MPEG2 Video-on-Demand (VoD) delivery in local multi-service IP networks. QOAS balances the need for high end-user quality with increased network utilisation, regardless of the nature of other cross traffic. A high utilisation would allow an increased number of customers to be served from a limited infrastructure, minimising the costs, but decreasing the end-user quality. The goal of QOAS is to maximise end-user perceived quality and links’ utilisation in the existing network conditions. QOAS varies the transmitted quantity of video data by dynamically adjusting the quality of the streamed video. In comparison with other approaches [3], its novelty is that these adjustments are carried out based on client-computed quality scores that describe the current quality of delivery sent via regular feedback. These scores include shortterm and long-term assessments of both the end-user perceived video quality [1] and IP performance parameters (e.g. delay, jitter, loss rate). During transmission the video quality is varied in a controlled manner according to the feedback reports. It requires fewer negative quality scores to trigger a quality decrease than positive for an increase. This ensures a fast reaction during bad delivery conditions helping to eliminate their cause and makes sure that quality upgrades are performed only after the network conditions have improved.}, keywords = {MPEG,QoS,IP Networks}, author = {G.Muntean and P.Perry and L.Murphy} }
@proceedings { 366, title = {Selecting Among Replicated Rate-Adaptive Multimedia Servers}, year = {2003}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Content/media replication is an important technique for improving the scalability and performance of a media delivery system. The efficient utilization of a set of replica servers hinges upon the ability to appropriately allocate servers to clients. In this paper, we present a probe based Server Selection System that has been specifically designed to work as a complementary technology with an existing Rate-adaptive Multimedia Streaming Application. The server selection process is driven by multimedia-media specific QoS metrics. The goal of the selection system is to direct clients to those servers whose paths are best equipped to fulfil the real-time requirements of the streaming media application while attempting to optimise the performance of the complementary rate-adaptive scheme.}, keywords = {Web Server,Multimedia}, author = {M.Searles and L.Murphy} }
@proceedings { 363, title = {User-Perceived Quality-Aware Adaptive Delivery of MPEG-4 Content}, year = {2003}, publisher = {Performance Engineering Lab}, address = {Monterey,California}, abstract = {Many adaptive delivery mechanisms have been devised for streaming multimedia over best-effort IP networks. Most of these adaptive schemes do not consider the user’s perception of quality when making adaptations. We propose that an optimum adaptation trajectory exists which indicates how encoding quality should be adapted (upgraded/downgraded) with respect to user perceived quality in response to network conditions. This optimum adaptation trajectory can be used with any transmission adaptation policy. We describe a system architecture that uses knowledge of user perceived quality to make adaptation decisions and give an example of how this knowledge can be used to complement the sender-based adaptation algorithm, LDA.}, keywords = {Quality, Perception, Multimedia, Adaptation algorithm}, author = {N.Cranley and P.Perry and L.Murphy} }
@proceedings { 358, title = {VoIP Playout Buffer Adjustment using Adaptive Estimation of Network Delays}, year = {2003}, publisher = {UCD}, address = {Berlin,Germany}, abstract = {The poor quality of Voice over IP can be improved by adaptive playout buffering at the receiver. This technique dynamically adapts the playout deadline to network conditions, thus minimizing both late packet loss and buffering time. A standard playout buffer strategy uses an estimate (Exponentially Weighted Moving Average) of the mean and variance of network delay to set the playout deadline. This estimation is characterized by a fixed, constant weighting factor. We show that tuning of this parameter so that the strategy works very well for all network conditions is not feasible. Therefore we propose to extend this standard buffer strategy by replacing the fixed, constant weighting factor with a dynamic one. In our solution, the weighting factor is dynamically adjusted according to the observed delay variations. When these variations are high (which implies that the network conditions are changing), the parameter is set low, and vice-versa. This allows rapid adaptation to network variations and reduces the frequency of late packets (or buffering time). Simulations and experimental results show that with our strategy, the trade-off between buffering delay and late packet loss at the receiver is improved significantly.}, keywords = {VoIP,Internet}, author = {M.Narbutt and L.Murphy} }
@inproceedings { 276, title = {A Framework for Performace Monitoring,Modelling & Prediction of Component Oriented Distributed Systems}, booktitle = {ACM 3rd International Workshop on Software and Performance }, year = {2002}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {We present a framework that can be used to identify performance issues in component-oriented distributed systems. The framework consists of a monitoring module, a modelling module and a prediction module, that are interrelated. The monitoring block extracts real-time performance data from a live or under development system. The modelling block generates UML models of the system showing where the performance problems are located and drives the monitoring process. The performance prediction block simulates different system-loads on the generated models and pinpoints possible performance issues. The technological focus is currently on Enterprise Java Beans systems.}, keywords = {Component Oriented}, author = {Mos,A. and Murphy,J.} }
@inproceedings { 279, title = {Algorithms for Resource Allocation in Data Transfer over EGPRS Network}, booktitle = {2nd European Conference on Universal Multiservice Networks}, year = {2002}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Mobile telephone systems are undergoing a substantial change from voice based systems which also support data transfer to become systems which truly support packet switched data services to mobile subscribers. This evolution towards the third generation (3G) mobile system will be based on the Global System for Mobile communications (GSM) [1] and will begin with the General Packet Radio Service (GPRS) [2], [3]. Finally the additional channel capacity offered by the Enhanced Datarates for Global Evolution (EDGE) will bring 3G services to users of these systems. This final system is often regarded as part of the 3G family and is referred to as Enhanced GPRS (EGPRS). Our goal is to investigate the efficiency of different algorithms used for resource allocation in data transfer over EGPRS networks. We consider a number of users in a cell that want either to send or to receive data and a centralized controller known as the Packet Control Unit (PCU). The PCU is the part of the Base Station Sub-system (BSS) which performs the arbitration mechanism to share the radio resources between users. The users can use nine different channel coding schemes, each one allowing a certain bit rate, but for the purposes of this discussion it is assumed that users can only use coding schemes one and two (CS1 and CS2) as a higher degree of flexibility is unimportant to this investigation. }, keywords = {Wireless, Mobile, GPRS, Enhanced GPRS, resource allocation algorithms}, author = {Todinca,D. and Perry,P. and Murphy,J.} }
@inproceedings { 412, title = {A Framework for Optical Deployment Scheme in Component-based Systems}, booktitle = {10th Conference on Software,Telecommunications & Computer Networks}, year = {2002}, abstract = {Lately, multimedia-related Internet applications have become very popular, and make up an increasing percentage of network traffic. This paper presents a quality-of-transmissionorientated adaptive mechanism for streaming of pre-recorded multimedia content. It aims to maintain the continuity of both the transmission and the remote stream play-out, at the expense of varying the stream's quality. A feedback scheme, in conjunction with a quality of transmission grading scheme, allows the server to learn the current network conditions. During transmission, the server can switch between different quality versions of the same multimedia content at certain checkpoints to modify the quality of the overall streaming process, and therefore the transferred quantity of data. Preliminary statistical and user perceptual test results from our prototype system show that in increased traffic conditions, the users' satisfaction was higher than if a receiver buffering solution was used.}, keywords = {Internet Applications,Multimedia,Network Traffic}, author = {N.Dumitrascu and L.Murphy} }
@inproceedings { 437, title = {An Adaptive Mechanism for Pre-recorded Multimedia Streaming Based on Traffic Conditions}, booktitle = {11th W3C WWW Conference}, year = {2002}, abstract = {The multimedia streams transmissions, done over the existing "best-effort" networks, are continuously increasing in number, making network congestion more likely to appear. The paper presents a traffic-based adaptive technique for transmitting pre-recorded multimedia streams, regardless the network condition. The adaptive mechanism is implemented by a feedback-controlled multimedia system which ensures continuous transmissions and play-out of streams even in congested network conditions. The measures taken into account vary the quantity of streamed data with the expense of modifying the streams' quality. Experimental results show improved behavior of the system in highly changing network conditions.}, keywords = {Adaptive transmission, multimedia streaming, traffic-based, feedback-control}, author = {Gabriel-Miro Muntean and L.Murphy} }
@proceedings { 411, title = {Adaptive Pre-recorded Multimedia Streaming}, year = {2002}, address = {Taipei,Taiwan}, abstract = {Lately, multimedia-related Internet applications have become very popular, and make up an increasing percentage of network traffic. This paper presents a quality-of-transmissionorientated adaptive mechanism for streaming of pre-recorded multimedia content. It aims to maintain the continuity of both the transmission and the remote stream play-out, at the expense of varying the stream's quality. A feedback scheme, in conjunction with a quality of transmission grading scheme, allows the server to learn the current network conditions. During transmission, the server can switch between different quality versions of the same multimedia content at certain checkpoints to modify the quality of the overall streaming process, and therefore the transferred quantity of data. Preliminary statistical and user perceptual test results from our prototype system show that in increased traffic conditions, the users' satisfaction was higher than if a receiver buffering solution was used.}, keywords = {Multimedia,Internet Streaming,Remote Stream Play-out}, author = {G.Muntean and L.Murphy} }
@proceedings { 413, title = {Adaptive Traffic-based Techniques for Live Multimedia Streaming}, year = {2002}, address = {Beijing,China}, abstract = {The growing number of multimedia stream transmissions done through the existing "best-effort"-based networks contributes to the increased traffic conditions. The latter affect the time-sensitive applications and especially the continuity of multimedia streaming. The paper presents some adaptive techniques for transmitting live multimedia streams over the Internet, regardless the overall traffic conditions. Their goal is to maintain the continuity of both the transmission and the remote play out processes by varying the streams' quality. A feedback-controlled multimedia system was built in order to allow for the deployment and testing of the proposed adaptive mechanisms. Some experimental results show that the continuity has been maintained even in highly changing network conditions.}, keywords = {Multimedia Streaming,Internet Traffic}, author = {G.Muntean and L.Murphy} }
@proceedings { 414, title = {Adaptive Multicast Architecture for Streamed MPEG-4 over IP Networks}, year = {2002}, address = {Cork,Ireland}, abstract = {Currently multimedia is either downloaded before viewing, or streamed over a network. However, streaming real-time or near real-time applications with a specified Quality of Service (QoS) over best-effort IP networks is not yet a solved problem. The Real-time Transport Protocol (RTP) can be used to facilitate streaming, but also has the potential to support QoS. Multicast transmissions are currently quite static and inflexible as all users receive the same treatment and it is only the network behaviour which differentiates between their perceived QoS. By gathering network statistics during the session and defining different customer groups, we propose to adapt multicast multimedia streaming to a fluctuating network load and/or client requests, thereby providing adaptive QoS.}, keywords = {QoS,IP Networks,Multimedia Streaming}, author = {M.Searles and N.Cranley and L.Murphy} }
@proceedings { 416, title = {A Novel Traffic-Based Adaptive Technique for Feedback-Controlled Transmissions of Pre-Recorded Multimedia Streams}, year = {2002}, abstract = {The multimedia streams transmissions, done over the existing "best-effort" networks, are continuously increasing in number, making network congestion more likely to appear. The paper presents a traffic-based adaptive technique for transmitting pre-recorded multimedia streams, regardless the network condition. The adaptive mechanism is implemented by a feedback-controlled multimedia system which ensures continuous transmissions and play-out of streams even in congested network conditions. The measures taken into account vary the quantity of streamed data with the expense of modifying the streams' quality. Experimental results show improved behavior of the system in highly changing network conditions.}, keywords = {Adaptive transmission, multimedia streaming, traffic-based, feedback-control}, author = {G.Muntean and L.Murphy} }
@proceedings { 417, title = {A Clients Perception Based Adaptive Web Server Application}, year = {2002}, address = {Honolulu,Hawaii}, abstract = {The Web is continually increasing in size and importance and so does the interest of the Web server administrators to maximize their users' satisfaction, while efficiently using the existing resources. The paper proposes an adaptive Web server application that tries to increase the performance of the Web server that hosts a Web site, as seen from the clients' point of view. The adaptiveness is based on the customization of the Web site in a manner that emphasizes the interests of the clients. Our tests show that both the user satisfaction and the server performance are improved.}, keywords = {Web server performance, customer satisfaction, adaptive Web server, and performance parameters}, author = {C.Hava and J.McManis and J.Murphy and L.Murphy} }
@inproceedings { 274, title = {Framework for predicting the performance of Component based Systems}, booktitle = {IEEE 10th International Conference on Software,Telecommunications and Computer Networks}, year = {2002}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The performance of component-based systems, especially of e-commerce applications, becomes a key factor in keeping business relations active. Middleware performance offered by technologies such as EJB, .NET, CORBA does not guarantee the fulfilment of performance requirements. We propose a framework that automatically builds an analytical model and drives possible performance improvements of the system under study. We outline a methodology of discovering transactions within the system at run-time. }, keywords = {E-Commerce}, author = {Mania,D. and Murphy,J.} }
@inproceedings { 277, title = {Novel Prioritised EGPRS Medium Access Regime For Reduced File Transfer Delay During Congested Periods}, booktitle = {IEE 3G 2002;Third International Conference on 3G Mobile Communications Technologies}, year = {2002}, abstract = {The goal of this paper is to investigate the efficiency of different algorithms used for resource allocation in data transfer over EGPRS networks. The focus is on the efficiency during congested periods in order to ensure reduced file transfer delay. A number of algorithms are presented for the resource allocation, and some generic mathematical results are presented for a two coding system. Simulation is relied on to produce results for the algorithms and it is found that Iterative Round Robin (IRR) and Oldest Queue (OQ) produce the best results. These are then proposed to be good candidates for implementing transmission control.}, keywords = {GPRS }, author = {Todinca,D. and Perry,P. and Murphy,J.} }
@inproceedings { 275, title = {Performance Management in Component-Oriented Systems using a Model Driven Architecture Approach}, booktitle = {IEEE 6th International Enterprise Distributed Object Computing Conference}, year = {2002}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Developers often lack the time or knowledge to profoundly understand the performance issues in large-scale component-oriented enterprise applications. This situation is further complicated by the fact that such applications are often built using a mix of in-house and Commercial-Off-The-Shelf (COTS) components. This paper presents a methodology for understanding and predicting the performance of component-oriented distributed systems both during development and after they have been built. The methodology is based on three conceptually separate parts: monitoring, modelling and performance prediction. Performance predictions are based on UML models created dynamically by monitoring-and-analysing a live or under-development system. The system is monitored using non-intrusive methods and run-time data is collected. In addition, static data is obtained by analysing the deployment configuration of the target application. UML models enhanced with performance indicators are created based on both static and dynamic data, showing performance hot spots. To facilitate the understanding of the system, the generated models are traversable both horizontally at the same abstraction level between transactions, and vertically between different layers of abstraction using the concepts defined by the Model Driven Architecture. The system performance is predicted and performance-related issues are identified in different scenarios by generating workloads and simulating the performance models. Work is under way to implement a framework for the presented methodology with the current focus on the Enterprise Java Beans technology.}, keywords = {Component Oriented}, author = {Mos,A. and Murphy,J.} }
@article { 415, title = {Time Synchronization for VoIP Quality of Service}, journal = {IEEE Internet Computing}, volume = {25-26}, year = {2002}, pages = {6 Pages}, publisher = {IEEE}, abstract = {Although packet-based and unmanaged networks like the Internet are ideal for delivering timeinsensitive data such as e-mail or static Web traffic, the growing demand for Web-based multimedia data exposes the limitations of core Internet protocols. With no end-to-end delay bounds, the public Internet’s best-effort service is unsuitable for delivering time-sensitive data and for interactive applications such as voice-over-IP. Normal speech consists of talkspurts, which typically last a few hundred milliseconds, and silence periods, which occur both within a spoken word and between words. In a packet-based network, voice packets are generated periodically at the sender and transmitted across the network. To cope with the packet interarrival variance inherent in besteffort service, current VoIP implementations generally implement fixed buffer schemes. Fixed buffer schemes make no attempt to match receiver operation to current network performance. An alternative approach is to use a more complex adaptive buffer scheme. This continuously matches playout delay to network conditions, at the expense of some packet loss due to late arrivals and some distortion of intertalkspurt silence periods. Various approaches seek to optimize the quality of service of VoIP applications (see the sidebar, “Quality of Service for VoIP,” next page, for a categorization of QoS approaches). We propose a system that uses synchronized time to combine the useful characteristics of both fixed and adaptive buffer strategies, thereby improving VoIP quality of service. Using a combination of global positioning system (GPS) technologies and the network time protocol (NTP), hosts can learn the precise end-to-end delay for each packet. This information can benefit both domestic and business Internet telephony users. In this article, we outline our proposed system and discuss issues arising from the use of synchronized time.}, keywords = {Web Traffic,Web-based Multimedia,VoIP}, author = {H.Melvin and L.Murphy} }
@inproceedings { 273, title = {Transaction Distribution Algorithms with user Classes for Distributed Application Performance Optimisation}, booktitle = {IEEE 10th International Conference on Software,Telecommunications and Computer Networks}, year = {2002}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {There is a growing need for high performance enterprise distributed systems that provide the scalability and availability required by modern enterprise portals and ecommerce systems. New technologies such as Enterprise Java Beans help building these systems by providing the framework to support such increasingly complex applications. The need for different response times for transactions, according to the situation, is often not taken into account. We present a new approach for optimising the overall response time of the system, introducing transaction priorities.}, keywords = {Reusablity of Software}, author = {Ciuhandu,O. and Murphy,J. } }
@inproceedings { 278, title = {Understanding Performance Issues in Component-Oriented Distributed Applications:The COMPAS Framework}, booktitle = {7th International Workshop on Component-Oriented Programming of the 16th European Conference on Object Oriented Programming}, year = {2002}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {Large enterprise applications such as financial systems are increasingly making use of Commercial-Off-The-Shelf (COTS) components in order to reduce development costs and increase productivity. Developers of such applications use productivity frameworks and component-oriented middleware such as EJB or .NET that help the development effort by providing run-time environments with support for a wide range of system-level services such as transactions and load-balancing. Due to the inherent complexity of such environments, it is often difficult to model and predict the performance of the resulting application, particularly when COTS components are used. We propose a framework that uses three interrelated modules to help developers understand and predict performance problems in component-oriented applications. The monitoring module extracts performance data in real-time from a running application. The modelling module generates UML models based on performance measurements from the monitoring module. Finally, the performance prediction module simulates the generated models for different workloads, helping developers understand the consequences of changes in user behaviour or changes in application design. Work is under way to implement the framework, with the current focus on the EJB platform.}, keywords = {Component Oriented}, author = {Mos,A. and Murphy,J.} }
@inproceedings { 270, title = {A New Dynamic Web Server}, booktitle = {8th International Conference on Telecommunication}, year = {2001}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The growth of traffic on the Internet and the explosion in the number of Web sites created in recent years make Web server performance an important issue for Web site designers. To improve the server's performance, it is necessary to determine the main factors affecting it before proposing new solutions for Web server design. Here we first present some experimental results on factors which influence Web server performance. We show how the number of concurrent clients accessing the server and the overall network traffic dynamics affect the performance. The details of a Web page’s composition are also studied to determine their effect on performance. Then we describe a new approach for developing a Web server, in which the server takes its performance as the clients see it into account and dynamically generates the requested Web pages. Their content depends on the traffic conditions and client capabilities. Some results are described to show the feasibility of our proposed design.}, keywords = {Web Servers}, author = {Hava-Muntean,C. and McManis,J. and Murphy,J.} }
@inproceedings { 272, title = {A Client-Oriented Dynamic Web Server}, booktitle = {IEE 17th UK Teletraffic Symposium}, year = {2001}, publisher = {N/A}, organization = {N/A}, abstract = {The cost of computer systems has decreased continuously in recent years, leading to an exponential growth in the number of computer users. In such an environment, more and more Web servers have been created offering many types of information. As a result Internet traffic has grown significantly, affecting the quality of the services offered by the Web servers. We propose a new approach for designing Web servers, which takes into account client requirements and constraints, and whose implementation is based on Java servlet and applet technology. This client-orientated Web server classifies each client into one of a number of pre-defined categories. The Web page generated for a client then depends on the client's current category. A Web page generated in this way may differ from one generated for another client in its content, number of images, graphic design and structure.}, keywords = {Web Servers}, author = {Hava-Muntean,C. and McManis,J. and Murphy,J. and Murphy,L.} }
@inproceedings { 466, title = {Adaptive Anti-Jitter Mechanism for Multi-Party Conferencing in a H.323 Multi Point Control Unit}, booktitle = {IEI/IEE Symposium on Tlecommunications System Research}, year = {2001}, abstract = {In this paper we propose a mechanism that can support multi-party conferencing. The main objective of this mechanism is to minimize effect of delay jitter. We have tested this mechanism in the Internet using H.323 terminals and H.323 Multipoint Control Unit. Our results show that the playout algorithms traditionally designed to work in the receiving endpoints can also be successfully implemented in the Multipoint Control Unit. As a result one can lower the rate of lost packets due to their late arrival.}, keywords = {Delay,Jitter}, author = {M.Narbutt and L.Murphy} }
@proceedings { 350, title = {Adaptive Playout Buffering for H.323 Voice over IP applications}, year = {2001}, publisher = {UCD}, abstract = {In this paper we investigate the performance of various buffer algorithms that might be implemented in H.323 VoIP applications. The main objective of those algorithms is to minimize effect of the delay jitter. We have tested those algorithms in the Internet using H.323 VoIP terminals. Our results show that the algorithm proposed by us can achieve the lowest rate of lost packets while adding acceptably small delays.}, keywords = {VoIP,Internet}, author = {M.Narbutt and L.Murphy} }
@proceedings { 351, title = {Adaptive Quality of Service for Streamed MPEG-4 over the Internet}, year = {2001}, publisher = {Performance Engineering Lab}, address = {Helsinki,Finland}, abstract = {Currently multimedia is either downloaded before viewing, or streamed over a network. However, streaming real-time or near real-time applications with a specified Quality of Service (QoS) over the Internet is not yet a solved problem. The Real-time Transport Protocol (RTP) can be used to facilitate streaming, but also has the potential to support QoS. By gathering network statistics during the session and defining different QoS levels, we propose to adapt multimedia streaming to a fluctuating network load and/or client requests, thereby providing adaptive QoS. We describe the simple server and client applications we have implemented to illustrate this adaptation process.}, keywords = {QoS,RTS,Internet}, author = {N.Cranley and L.Murphy} }
@proceedings { 352, title = {A Novel Feedback Controlled Multimedia Transmission Scheme}, year = {2001}, publisher = {Performance Engineering Lab}, address = {Bucharest,Romania}, abstract = {The number of multimedia transmissions over the existing network infrastructure is continually increasing. This leads to longer periods of network congestion which affects these transmissions and hence their playout. We propose a novel feedback controlled multimedia transmission scheme in order to ensure continuous stream delivery and play-out, even in the case of network congestion. Data transmission and the exchange of control information are done via a doublechannel (TCP and UDP) link. A special protocol (Client Initiated Protocol) has been defined to provide the transmission mechanism with a reduced overhead. We describe both its components, the Client Initiated Streaming Protocol (CISP) used for control and the Client Initiated Transport Protocol (CITP) used for data transmissions. We also present the feedback scheme and describe the server's possible state transitions. A multicast approach is explored and its advantages and disadvantages outlined. We present some experimental results to show the functionality of our scheme.}, keywords = {Multimedia,TCP/UDP}, author = {G.Muntean and L.Murphy} }
@proceedings { 353, title = {A New Dynamic Web Server }, year = {2001}, publisher = {Performance Engineering Lab}, address = {Bucharest,Romania}, abstract = {The growth of traffic on the Internet and the explosion in the number of Web sites created in recent years make Web server performance an important issue for Web site designers. To improve the server's performance, it is necessary to determine the main factors affecting it before proposing new solutions for Web server design. Here we first present some experimental results on factors which influence Web server performance. We show how the number of concurrent clients accessing the server and the overall network traffic dynamics affect the performance. The details of a Web page’s composition are also studied to determine their effect on performance. Then we describe a new approach for developing a Web server, in which the server takes its performance as the clients see it into account and dynamically generates the requested Web pages. Their content depends on the traffic conditions and client capabilities. Some results are described to show the feasibility of our proposed design.}, keywords = {Internet,QoS,Web Server}, author = {C.Hava and J.McManis and J.Murphy and L.Murphy} }
@proceedings { 355, title = {Adaptive Playout Buffering for Audio/Video transmission over the Internet}, year = {2001}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Transmitting real-time audio/video over the Internet is very difficult due to packet loss and jitter. These parameters vary depending on the locations of the senders and receivers, with typical packet loss rates of 0−20% and one-way delays of 5-500 ms. Delay variations occur within and across audio and video streams, complicating the synchronization process. One possibility for reducing jitter involves buffering audio and video packets at the receiver, so that slower packets arrive in time to be played out in the correct sequence at the appropriate times. This paper presents various adaptive playout buffer algorithms that minimize the effect of delay jitter. We evaluate their effectiveness through experiments based on a real network and compare their performance in terms of delay/packet loss ratios. Although the main focus of this paper is the playout buffering for audio, the synchronization between audio and video streams is also specified.Transmitting real-time audio/video over the Internet is very difficult due to packet loss and jitter. These parameters vary depending on the locations of the senders and receivers, with typical packet loss rates of 0−20% and one-way delays of 5-500 ms. Delay variations occur within and across audio and video streams, complicating the synchronization process. One possibility for reducing jitter involves buffering audio and video packets at the receiver, so that slower packets arrive in time to be played out in the correct sequence at the appropriate times. This paper presents various adaptive playout buffer algorithms that minimize the effect of delay jitter. We evaluate their effectiveness through experiments based on a real network and compare their performance in terms of delay/packet loss ratios. Although the main focus of this paper is the playout buffering for audio, the synchronization between audio and video streams is also specified.}, keywords = {Internet,Online-Streaming}, author = {M.Narbutt and L.Murphy} }
@proceedings { 356, title = {Adaptive Quality of Service for Streamed MPEG-4 over the Internet}, year = {2001}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Currently multimedia is either downloaded before viewing, or streamed over a network. However, streaming real-time or near real-time applications with a specified Quality of Service (QoS) over the Internet is not yet a solved problem. The Real-time Transport Protocol (RTP) can be used to facilitate streaming, but also has the potential to support QoS. By gathering network statistics during the session and defining different QoS levels, we propose to adapt multimedia streaming to a fluctuating network load and/or client requests, thereby providing adaptive QoS. We describe the simple server and client applications we have implemented to illustrate this adaptation process.}, keywords = {RTP,QoS}, author = {N.Cranley and L.Murphy} }
@proceedings { 465, title = {An Investigation into the use of Synchronised Time to Improve VoIP Service }, year = {2001}, abstract = {This paper presents an overview of work in progress relating to the use of synchronised time in Voice over IP (VoIP) networks. One of the principal limita- tions of conventional IP networks is the best-e�ort service that they provide. In recent years, the In- ternet Engineering Task Force (IETF) have created the multimedia data and control architecture which incorporates protocols such as the Realtime Trans- port Protocol (RTP), RTP Control Protocol (RTCP) and Real Time Streaming Protocol (RTSP). Whilst these protocols assist in delivery of multimedia traÆc, the lack of bounds on end-to-end delay still presents signi�cant problems for interactive applications such as VoIP. The ITU-T recommendation G.114 speci�es that a round-trip-delay of 300ms should not be ex- ceeded and the Plain Old Telephone System (POTS) generally does much better than this. Along with RTP and RTCP, various approaches have been pro- posed and taken to improve the performance of VoIP networks from an interactive viewpoint. These range from sender-based codec measures to network-based policies that di�erentiate between traÆc ows and �- nally to various bu�er schemes at the receiver that balance overall delay with receiver packet loss due to late arrival. This paper summarises much of this work but focuses on receiver-based measures. RTP timestamps are principally used to enable re- ceiver hosts to monitor and react to the inter-packet delay variance (jitter). RTCP packet timestamps fur- ther enable sender hosts to periodically determine round-trip-times (RTT). Such calculations do not re- quire that end host clocks are synchronised. In this paper, a scheme is described whereby syn- chronised time is available to hosts in a VoIP ses- sion. As Global Positioning System (GPS) receivers become increasingly cost-e�ective and always-on In- ternet connections more prevalent, VoIP hosts can avail of synchronised time either via GPS or Network Time Protocol (NTP). This time synchronisation en- ables each host to know precisely the end-to-end de- lays on a packet-by-packet basis. This is a signi�- cant improvement on the present situation whereby sender hosts can periodically determine round-trip- times and thus estimate one-way-delays. Most adap- tive receiver bu�er schemes do not consider such es- timates and are designed to minimise delay at the expense of tolerable packet loss due to late arrival and some distortion of inter-talkspurt silence peri- ods. In many instances, the performance of private IP networks and the localised public Internet will op- erate well within the bounds of G.114. In such sit- uations, a �xed end-to-end delay within the G.114 bounds yet marginally above the actual end-to-end performance would result in a tolerable delay with no late packet loss and no distortion of silence pe- riods. With synchronised time, supporting protocols and receiver-based intelligence, such a system can be implemented.}, keywords = {VoIP,IP Networks}, author = {H.Melvin and L.Murphy} }
@proceedings { 354, title = {Experimental Results for a Feedback-Controlled Multimedia Transmission System}, year = {2001}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Multimedia transmissions over IP networks have increased significantly in recent years. Both user expectations and traffic levels have increased as well. One way to take these into account is for senders to receive and respond to feedback about the quality of their transmissions. We have built a feedback controlled multimedia transmission system, and we have tested and analysed the influence of various factors on transmission performance. This paper presents the results of some of these tests, and suggests some solutions for improving the quality of multimedia transmissions under network congestion.}, keywords = {Multimedia,IP}, author = {G.Muntean and L.Murphy} }
@article { 349, title = {Feedback Controlled Traffic Shaping for Multimedia Transmission in a Real-Time Client-Server System}, year = {2001}, publisher = {UCD}, abstract = {The number of applications requiring real-time transmission of multimedia streams over the existing network structure is increasing. Large amounts of digital video, audio and text data of continuous nature and with associated timing constraints are thus being exchanged, making network overloads more likely. Our paper presents a feedbackcontrolled solution for ensuring a continuous transmission and play-out of MPEG streams even in congested network conditions. A doublechannel link (TCP and UDP) allows data to be sent from the server to the client, and control information describing the quality of the transmission to be sent between client and server. The control data is collected by a special unit located at the client which regularly inspects the receiver and driver buffers. The control data received from the client is processed by a feedback manager at the server which controls a transmission shaper. The latter can influence the transmission process by modifying parameters such as the transmission buffer size and the transmission frequency. Experimental results show improved behavior of the system in congested network conditions.}, keywords = {Real-Time,Multimedia Streams}, author = {G.Muntean and L.Murphy} }
@inproceedings { 269, title = {New Methods for Performance Monitoring of J2EE Applications Servers}, booktitle = {IEEE 8th International Conference on Telecommunications}, year = {2001}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {There is a growing need for high performance enterprise distributed systems that provide the scalability and availability required by modern enterprise portals and ecommerce systems. New technologies such as Enterprise Java Beans help building these systems by providing the framework to support the increasingly complex applications. Their performance, however, is not guaranteed by the technology itself and it is mostly the responsibility of the developers to build the application so that it meets the required performance needs. We present a number of approaches for monitoring existing Enterprise Java Beans applications in order to help the developers identify performance problems at an object-oriented level.}, keywords = {Applications Servers}, author = {Mos,A. and Murphy,J.} }
@inproceedings { 267, title = {Performance Monitoring of JAVA Component-Oriented Distributed Applications}, booktitle = {IEEE 9th International Conference on Software,Telecommunication & Computer Networks}, year = {2001}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {We present a framework for monitoring the performance of component oriented distributed applications based on the Enterprise Java Beans specification. The environment leverages EJB architecture to monitor existing applications in real-time and to provide detailed run-time information that help identify performance hotspots at an object-oriented level. It is non-intrusive, portable across all EJB compliant application servers and easily extendable to accommodate new data-acquisition or graphical presentation components. Current status of the work serves as proof of concept and a complete implementation is under development.}, keywords = {performance, monitoring, EJB, component-oriented, distributed systems}, author = {Mos,A. and Murphy,J.} }
@inproceedings { 271, title = {Resource Allocation for Interactive traffic classes over GPRS Network}, booktitle = {IEE 17th UK Teletraffic Symposium}, year = {2001}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {The General Packet Radio Service (GPRS) is a new bearer service for GSM that greatly simplify wireless access to packet data networks, e.g., to the Internet, to the corporate LAN or to the mobile portals. It applies a packet radio standard to transfer user data packets in a well-organized way between Mobile Stations (MS) and external packet data networks. The introduction of guaranteed performance services in GPRS networks requires detailed studies of the resource allocation and service integration issue. This paper proposes some different schemes of allocating the physical channels to mobile stations. We consider the integration of voice and data over Time Division Multiple Access wireless cellular networks. We describe different radio resource allocation algorithms, and describe their similarities and differences in the context of GSM and GPRS networks. However these algorithms can be used for diversified types of wireless networks. In this paper we consider the interactive best effort traffic class as one of the most important traffic classes in GPRS.}, keywords = {GPRS }, author = {Nowicki,E. and Murphy,J.} }
@inproceedings { 268, title = {The Influence of Web Page Images on the Performance of Web Servers}, booktitle = {International Confrence on Networking}, year = {2001}, publisher = {Performance Engineering Lab}, organization = {Performance Engineering Lab}, abstract = {In recent years World Wide Web traffic has shown phenomenal growth. The main causes are the continuing increase in the number of people navigating the Internet and the creation of millions of new Web sites. In addition, the structure of Web pages has become more complex, including not only HTML files but also other components. This has affected both the download times of Web pages and the network bandwidth required. The goal of our research is to monitor the download times of Web pages from different Web sites, and to find out to what extent the images contained in these Web pages influence these times. We also suggest some possible ways of decreasing the bandwidth requirements and download times of complex Web pages.}, keywords = {Web Servers}, author = {Hava-Muntean,C. and McManis,J. and Murphy,J.} }
@inproceedings { 266, title = {Assuring Performance in E-Commerce Section}, booktitle = {IEE 16th UK Teletraffic Symposium}, number = {29/1-29/7}, year = {2000}, publisher = {N/A}, organization = {N/A}, abstract = {Performance Assurance is a methodology that, when applied during the design and development cycle, will greatly increase the chances of an e-Commerce project satisfying user performance requirements first time round. This paper discusses the primary risk factors in development projects, the keys to a successful risk management programme, and the tools required. It also discusses problems that can occur in e-Commerce systems and some examples of how these might manifest themselves. A definition and the reasoning behind a performance assurance methodology is given, and the performance assurance methodology that is proposed is outlined.}, keywords = {E-Commerce}, author = {Murphy, J.} }
@proceedings { 346, title = {An Object-Oriented Prototype System for Feedback Controlled Multimedia Networking}, year = {2000}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Multimedia networking refers to the transfer of related audio, video, images, text and/or data among networked computers. Because of their very large filesize and their continuous nature, these transfers are problematic. Unlike the majority of proposed solutions for transmitting continuous media, which either request a dedicated connection or use connectionless protocols, we propose a solution which uses a connection-oriented protocol (TCP/IP). A dynamic feedback and buffering mechanism allows us to continue with the transmission even in the case that the network load increases, decreasing the necessary bandwidth by gradually reducing the quality of the transmitted stream. Transmission quality is restored when the network traffic reduces. An object-oriented approach is used to build both server and client, allowing easier system debugging and expansion. Multithreading is used to solve some problems which require concurrent solutions.}, keywords = {dynamic feedback scheme, audio/video synchronization, multimedia networking}, author = {G.Muntean and L.Murphy} }
@proceedings { 345, title = {Initial Tool for Monitoring Performance of Web Sites}, volume = {45(59)}, year = {2000}, publisher = {Performance Engineering Lab}, abstract = {A very important application, which offers access to information on the Internet, is the World Wide Web (WWW or Web). The WWW is primarily responsible for the growth of e-commerce activity by the use of the Internet. To improve users' satisfaction with e-commerce WWW services, a lot of work has been done on characterizing the performance of Internet applications and servers. We discuss in this article about a monitoring application for performance measurement of the WWW Servers. By observing the behaviour of WWW servers and measuring their performance, we can estimate several performance indices. Our application simulates the access of a number of clients to the same Web page and its links and analyses the results. Three different cases are taken into account: the clients access the same Web page one after the other (i.e. serially), at the same time (i.e. in parallel), checking before a ‘cache’ structure.}, keywords = {Web,Internet}, author = {C.Hava and S.Holban and J.Murphy and L.Murphy} }
@proceedings { 348, title = {Performance Measurement of World Wide Web Servers}, year = {2000}, publisher = {Performance Engineering Lab}, address = {Harlow,England}, abstract = {The World Wide Web (WWW, or Web) is one of the most important Internet services, and has been largely responsible for the increasing popularity of the Internet in recent years. The WWW continues to expand in both size and content, and is primarily responsible for the growth of e-commerce activity by the use of the Internet. To improve users' satisfaction with e-commerce WWW services, a lot of work has been done on characterizing the performance of Internet applications and servers. In this paper we outline a monitoring application for performance measurement of WWW servers. By observing the behaviour of WWW servers and measuring their performance, we can estimate several performance indices. Our monitoring application simulates the access of a number of clients to the same Web page and its links. Our simulator allows the user to choose different scenarios based on different ways clients can access a Web page, and compare the resulting times.}, keywords = {WWW Servers,Internet}, author = {C.Hava and L.Murphy} }
@proceedings { 347, title = {Quality of Service for Streamed Multimedia over the Internet}, year = {2000}, publisher = {Performance Engineering Lab}, address = {Dublin,Ireland}, abstract = {Multimedia is any combination of text, graphics, audio, video, animation and data. Multimedia applications over the Internet include Video on Demand (VoD), interactive video, and videoconferencing. However there are limitations to these applications, as it is often required that a multimedia file be completely downloaded before it can be played or viewed. Streaming is the ability to start processing data before all of it has arrived, thus making delivery in real-time or near real-time possible. Streaming technologies are designed to overcome the problem of limited bandwidth. The implication of this is that multimedia files of any size can be played/displayed over the Internet in real-time or near real-time. To date, there has been no definitive way to transmit streamed MPEG-4 files across the Internet with an associated Quality of Service. One possibility is to write a control protocol on top of TCP/IP, which manages the flow of multimedia data [1]. In this paper, an alternative approach using a protocol stack comprising a Real-time Transport Protocol (RTP) layer over a User Datagram Protocol (UDP)/Internet Protocol (IP) layer is described. Firstly we provide a brief description of MPEG/MPEG-4 and RTP/RTCP, followed by a description of the system implemented and plans for its future development.}, keywords = {Multimedia,Real-time}, author = {N.Cranley and L.Fiard and L.Murphy} }
@proceedings { 344, title = {Some Software Issues of a Real-Time Multimedia Networking System}, volume = {45(59)}, year = {2000}, publisher = {Performance Engineering Lab}, address = {Timisoara,Romania}, abstract = {The transmission of related multimedia data causes problems because of their very large size and continuous nature. Unlike the majority of the existing solutions for transmitting continuous media, which use connectionless protocols, we propose one that uses a connection-oriented protocol (TCP/IP). An object-oriented approach is used to build both server and client, allowing easier system debugging and expansion. We implemented a buffering mechanism which allows us to continue playing for a period when the network load increases. Multithreading is used to solve some problems which require concurrent solutions.}, keywords = {TCP/IP,Multimedia}, author = {G.Muntean and L.Murphy} }
@inproceedings { 265, title = {Why Worry about Performance in e-commerce Solutions}, booktitle = {IEE 16th UK Teletraffic Symposium}, year = {2000}, publisher = {E-Commerce Performance}, organization = {E-Commerce Performance}, abstract = {This paper will discuss the evolution of computer systems, and will show that while the system performance is getting increasingly critical, it is also getting harder to master performance assurance and to master the system evolution. This paper proposes that the real challenge posed currently for the performance engineer is the explosion of e-Commerce systems where the users are increasingly impatient and the design methodologies are in their infancy. The reason that the systems are getting more complex is that the system dynamics are critical to performance, but they are not addressed by traditional design methodologies. One solution to this is to use a performance assurance process that guarantees that the system dynamics are captured. Overall the odds are not good for building complex systems, but performance assurance can reduce risk by a factor of ten or more.}, keywords = {E-Commerce}, author = {Upchurch,E. and Murphy, J.} }
</bibtex>