Pubs:2004

<bibtex> @article{285, 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}, journal={Journal of Optical Communication}, year={2004}, pages={171-177(7Pages)}, volume={242}, 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}, pdf={ber performance.pdf}, } </bibtex> <bibtex> @inproceedings{286, author={Nowak,D.;Perry,P.;Murphy,J.}, title={Bandwidth Allocation For Service Level Agreement Aware Ethernet Passive Optical Networks}, booktitle={IEEE Globecom 2004}, year={2004}, 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}, pdf={bandwidth allocation.pdf}, } </bibtex> <bibtex> @inproceedings{287, author={Noonan,J.;Perry,P.;Murphy,J.}, title={Client Controlled Network Selection}, booktitle={IEE 5th International Conference on 3G Mobile Communication Technologies(3G 2004)}, year={2004}, 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}, pdf={client controlled.pdf}, } </bibtex> <bibtex> @inproceedings{288, author={Graja,H.;Peery,P.;Murphy ,J. }, 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}, 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}, pdf={analysis of delay.pdf}, } </bibtex> <bibtex> @inproceedings{289, author={Todinca,D.;Perry,P.;Graja,H.;Murphy,J.}, title={Novel Admission Control Algorithm for GPRS/EGPRS Based on Fuzzy Logic}, booktitle={IEE 5th International Conference on 3G Mobile Communication Technologies}, year={2004}, 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}, pdf={novel admission.pdf}, } </bibtex> <bibtex> @inproceedings{290, author={Graja,H;Perry,P.;Murphy J }, 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}, 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}, pdf={statistical analysis.pdf}, } </bibtex> <bibtex> @inproceedings{291, author={Nowak,D.;Perry,P.;Murphy,J.}, title={Adaptive Dynamic Bandwidth Allocation Algorithm for Ethernet PONs}, booktitle={30th European Conference on Optical Communications,ECOS 2004}, year={2004}, 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}, pdf={adaptive dynamic.pdf}, } </bibtex> <bibtex> @inproceedings{292, author={Nowak,D.;Perry,P.;Murphy,J.}, 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}, 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}, pdf={novel service.pdf}, } </bibtex> <bibtex> @inproceedings{293, author={Nowak,D.;Perry,P.; Murphy,J.}, 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}, 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}, pdf={bandwidth.pdf}, } </bibtex> <bibtex> @inproceedings{294, author={Parsons,T.;Murphy,J.}, 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}, 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}, pdf={framework for automatically.pdf}, } </bibtex> <bibtex> @inproceedings{295, author={Diaconescu,A.;Mos,A.;Murphy,J.}, title={Automatic Performance Management in Component Based Software Systems}, booktitle={IEEE International Conference on Autonomic Computing}, year={2004}, 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}, pdf={automatic performance.pdf}, } </bibtex> <bibtex> @inproceedings{296, author={Noonan,J.;Kelly,A.;Perry,P.;Murphy,S.;Murphy,J.}, title={Simulation of Multimedia Traffic over SCTP Modified for Delay-Centric Handover}, booktitle={5th World Wireless Congress(B3G)}, year={2004}, 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 LAN?s 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}, pdf={simulations.pdf}, } </bibtex> <bibtex> @inproceedings{297, author={Trofin,M.;Murphy,J.}, title={Using Runtime Information for Adapting Enterprise Java Beans Application Servers}, booktitle={2nd Internatioanl Workshop on Dynamic Analysis(WODA)}, year={2004}, 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}, pdf={using runtime.pdf}, } </bibtex> <bibtex> @inproceedings{298, author={Diaconescu,A.;Murphy,J.}, 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}, 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`}, pdf={framework.pdf}, } </bibtex> <bibtex> @inproceedings{299, author={Mos,A.; Murphy,J.}, 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}, 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`}, pdf={compas.pdf}, } </bibtex> <bibtex> @inproceedings{368, author={S.Goor;S.Murphy;L.Murphy}, title={Experimental Performance Analysis of RTP-based Transmission Techniques for MPEG-4}, booktitle={14th International Packet Video Workshop}, year={2004}, 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.}, pdf={experimental performance.pdf}, } </bibtex> <bibtex> @inproceedings{369, author={G.Cunningham;P.Perry;L.Murphy}, title={Application Layer Delay-Centric Handover of Streamed Video in a 4G Network}, booktitle={ITT 2004}, year={2004}, 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}, pdf={application layer.pdf}, } </bibtex> <bibtex> @inproceedings{370, author={G.Cunningham;P.Perry;L.Murphy}, title={Soft,Vertical Hadover of Streamed Video}, booktitle={IEE International Conference on 3G Mobile Communication Technologies}, year={2004}, 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.}, pdf={soft vertical.pdf}, } </bibtex> <bibtex> @inproceedings{371, author={N.Cranley;P.Perry;L.Murphy}, title={Perceptual Quality Adaptation(PQA) Algorithm for 3GP & Multi-Tracked MPEG-4Content over Wireless IP Networks}, booktitle={15th IEEE International Symposium on Personal,Indoor & Mobile Radio Communications}, 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}, pdf={perceptual quality.pdf}, } </bibtex> <bibtex> @article{372, author={G.Muntean;P.Perry;L.Murphy}, title={Performance Comparison of Local Area Video Streaming Systems}, journal={IEEE Communications Letters}, year={2004}, pages={326-328}, volume={8}, 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.}, pdf={performance comparison.pdf}, } </bibtex> <bibtex> @inproceedings{373, author={G.Muntean;P.Perry;L.Murphy}, title={Quality-Oriented Adaptation Scheme (QOAS) for High Bit-Rate Multimedia Streaming}, booktitle={6th International Conference on Technical Informatics(CONTI 2004)}, 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.}, pdf={quality oriented.pdf}, } </bibtex> <bibtex> @inproceedings{374, author={H.Melvin;L.Murphy}, title={An Evaluation of Delay-Aware Receiver Playout Strategies for VoIP Applications}, booktitle={Third IFIP-TC6 Networking Conference }, year={2004}, 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}, pdf={an evaluation.pdf}, } </bibtex> <bibtex> @article{375, author={G.Muntean;P.Perry;L.Murphy}, title={A New Adaptive Multimedia Streaming System for ALL-IP Multi Service Networks}, journal={IEEE Transactions on Broadcasting}, year={2004}, pages={1-10}, volume={50}, 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.}, pdf={new adaptive.pdf}, } </bibtex> <bibtex> @inproceedings{376, author={M.Narbutt;L.Murphy}, title={A New VoIP Adaptive Playout Algorithm }, booktitle={IEE Telecommunications Quality of Service:The Business of Success(QoS 2004)}, year={2004}, 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}, pdf={new voip.pdf}, } </bibtex> <bibtex> @inproceedings{422, author={D.McGuinness;L.Murphy;A.Lee}, 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,}, pdf={issues.pdf}, } </bibtex> <bibtex> @inproceedings{423, author={N.Cranley;P.Perry;L.Murphy}, 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}, pdf={content-based.pdf}, } </bibtex> <bibtex> @inproceedings{424, author={G.Muntean;P.Perry;L.Murphy}, 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}, pdf={performance assessment.pdf}, } </bibtex> <bibtex> @inproceedings{432, author={Muntean,C.H.;McManis,J.}, title={End-User Quality of Experience Layer for Adaptive Hypermedia Systems}, booktitle={3rd International Conference on Adaptive Hypermedia & Adaptive Web-Based 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}, pdf={end user.pdf}, } </bibtex> <bibtex> @inproceedings{433, author={Muntean,C.H.;McManis,J.}, title={QoSAHA:A Performance Oriented Learning System}, booktitle={AACE World Conference on Educational Multimedia,Hypermedia & Telecomm}, 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}, } </bibtex> <bibtex> @inproceedings{450, author={A.Kelly;Gabriel-Miro Muntean;P.Perry;J.Murphy}, 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}, pdf={delay.pdf}, } </bibtex> <bibtex> @inproceedings{464, author={S.Murphy;M.Searles;C.Rambeau;L.Murphy}, 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}, pdf={evaluating.pdf}, } </bibtex>