Pubs:2003

<bibtex> @inproceedings{280, author={Dantcha,A.;Barry,L.;Murphy J.;Dunne,J.;Mullane,T. ;Mcdonald,D.}, title={BER Performance in Wavelength Packet Switched WDM systems during Nano-Second Wavelength switching Events}, booktitle={29th European Conference on Optical Communications}, year={2003}, 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}, pdf={ber performance.pdf}, } </bibtex> <bibtex> @inproceedings{281, author={Kelly,A.;Perry,P. ;Murphy J}, 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}, 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}, pdf={modified sctp.pdf}, } </bibtex> <bibtex> @inproceedings{282, author={Trofin,M.;Murphy,J.}, title={A Self Optimizing Container Design for Enterprise Java Beans Applications}, booktitle={8th International Workshop on Component Oriented Programming}, year={2003}, 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}, pdf={self optimizing.pdf}, } </bibtex> <bibtex> @inproceedings{283, author={Graja,H.;Perry,P.;Todinca,D.;Murphy ,J. }, title={Novel GPRS Simulator for Testing MAC Protocols}, booktitle={IEE 4th International Conference on 3G Mobile Communication Technologies}, year={2003}, 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}, pdf={novel gprs.pdf}, } </bibtex> <bibtex> @inproceedings{284, author={Diaconescu,A.;Murphy,J.}, title={A Framework for Using Component Redundancy for Self Optimising & Self Healing Component Based Systems}, booktitle={International Conference on Software Engineering}, year={2003}, 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}, pdf={framework.pdf}, } </bibtex> <bibtex> @article{357, author={G.Muntean;P.Perry;L.Murphy}, title={Quality Oriented Adaptation Scheme for Video-On-Demand}, journal={IEE Electronic Letters}, year={2003}, pages={1689-1690}, volume={39}, 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}, pdf={quality oriented.pdf}, } </bibtex> <bibtex> @inproceedings{358, author={M.Narbutt;L.Murphy}, title={VoIP Playout Buffer Adjustment using Adaptive Estimation of Network Delays}, booktitle={International Teletraffic Congress ITC-18}, year={2003}, 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}, pdf={voip playout.pdf}, } </bibtex> <bibtex> @inproceedings{359, author={N.Dumitrascu;S.Murphy;L.Murphy}, title={A Methodology for Predicting the Performance of Component Based Applications}, booktitle={8th International Workshop on Component-Oriented Programming}, year={2003}, 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}, pdf={methodology.pdf}, } </bibtex> <bibtex> @inproceedings{360, author={M.Searles;P.Perry;L.Murphy}, title={Probe based Dynamic Server Selection for Multimedia QoS}, booktitle={First International Working Conference on Performance Modelling & Evaluation of Heterogenous Networks}, year={2003}, 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.}, pdf={probe based.pdf}, } </bibtex> <bibtex> @inproceedings{361, author={H.Melvin;L.Murphy}, title={An Integrated NTP-RTCP Solution to Audio Skwe Detection & Compensation for VoIP Applications}, booktitle={International Conference on Multimedia & Expo}, year={2003}, 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}, pdf={integrated ntp.pdf}, } </bibtex> <bibtex> @inproceedings{362, author={S.Goor;L.Murphy}, title={An Adaptive MPEG-4 Streaming System based on Object Prioritisation}, booktitle={Irish Signals & Systems Conference}, year={2003}, 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}, pdf={adaptive mpeg4.pdf}, } </bibtex> <bibtex> @inproceedings{363, author={N.Cranley;P.Perry;L.Murphy}, title={User-Perceived Quality-Aware Adaptive Delivery of MPEG-4 Content}, booktitle={13th International Workshop on Network & Operating Systems Support for Digital Audio & Video}, year={2003}, 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}, pdf={user perceived.pdf}, } </bibtex> <bibtex> @inproceedings{364, author={H.Melvin;L.Murphy}, title={An Evaluation of the Potential of Synchronised Time to improve VoIP Quality}, booktitle={International Conference on Communications}, year={2003}, 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}, pdf={an evaluation.pdf}, } </bibtex> <bibtex> @inproceedings{365, author={S.Goor;L.Murphy}, title={An Adaptive MPEG-4 Streaming System based on Object Prioritisation}, booktitle={IEI/IEEE Symposium on Telecommunications System Research}, year={2003}, 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.}, pdf={adaptive mpeg4.pdf}, } </bibtex> <bibtex> @inproceedings{366, author={M.Searles;L.Murphy}, title={Selecting Among Replicated Rate-Adaptive Multimedia Servers}, booktitle={IEI/IEEE Symposium on Telecommunications System Research}, year={2003}, 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}, pdf={selecting among.pdf}, } </bibtex> <bibtex> @inproceedings{367, author={G.Cunningham;L.Murphy}, title={Adaptive MPEG-4 transmission at the Wireless Transmitter}, booktitle={IEI/IEEE Symposium on Telecommunications System Research}, year={2003}, 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.}, pdf={adaptive mpeg4.pdf}, } </bibtex>