The seamless handover of streamed video in a WLAN with UDP as the transport layer is considered. ... more 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.
A recently standardized transport protocol -SCTP and the Mobile IP standard for IPv4 are examined... more A recently standardized transport protocol -SCTP and the Mobile IP standard for IPv4 are examined. Both these protocols have been suggested as offering some additional functionality to mobile users over and above that which is currently available from TCP/IP. Here, the interaction of these two new protocols is investigated through the examination of traffic flows through a number of network topologies. The results seem to suggest that although these protocols do work together, they do not currently provide all the functionality that a mobile user might desire. In particular, some limitations caused by implementations are highlighted that could be remedied by small modifications without the need to change either standard specification.
The characterisation and large-signal modelling of InGaAs pseudomorphic high electron mobility transistors
... Department of Electonic and Electrical Engineenng University College Dublin, Dublin 4, Irelan... more ... Department of Electonic and Electrical Engineenng University College Dublin, Dublin 4, Ireland Tel: +353-1-706 1908;Fax: +353-1-2830921; E-mail: [email protected] RaSa ... (3) Vgst =g5-VTO +'yt s where VIDis the pinch-off voltage and a; (3, & A, p are model parameters. ...
It is likely that an ensemble of overlapping heterogeneous wireless networks will be required to ... more 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.
Fifth IEE International Conference on 3G Mobile Communication Technologies (3G 2004) The Premier Technical Conference for 3G and Beyond, 2004
The delay characteristics of small IP packets in cellular data networks is investigated through t... more 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 traffic such as Voice over IP packets.
International Journal of Human-computer Studies / International Journal of Man-machine Studies, 2006
In general, video quality adaptation and video quality evaluation are distinct activities. Most a... more 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
The combination of increased data rates in 4G cellular networks (such as LTE Advanced), dedicated... more The combination of increased data rates in 4G cellular networks (such as LTE Advanced), dedicated multicast/broadcast services (e-MBMS) and the emergence of scalable video coding standards (H. 264 SVC) allow mobile operators to offer multimedia-...
A recently standardized transport protocol - SCTP and the Mobile IP standard for IPv4 are examine... more A recently standardized transport protocol - SCTP and the Mobile IP standard for IPv4 are examined. Both these protocols have been suggested as offering some additional functionality to mobile users over and above that which is currently available from TCP/IP. Here, the interaction of these two new protocols is investigated through the examination of traffic flows through a number of
2008 Conference on Lasers and Electro-Optics, 2008
Authors present a cost efficient narrow linewidth laser transmitter for future coherent detection... more Authors present a cost efficient narrow linewidth laser transmitter for future coherent detection systems. The spectral purity of the laser allows the phase modulation of data signals at bit rates as low as 155 Mb/s.
Ethernet Passive Optical Networks (EPONs) have attracted considerable attention from industry as ... more Ethernet Passive Optical Networks (EPONs) have attracted considerable 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 centralized environment can deliver good performance in terms of average and maximum packet delay. In this paper two new algorithms are introduced that target SLAaware EPONs and provide a good protection of offered quality of service against interference from other sources.
Bugs in a project, at any stage of Software life cycle development are costly and difficult to fi... more Bugs in a project, at any stage of Software life cycle development are costly and difficult to find and fix. Moreover, the later a bug is found, the more expensive it is to fix. There are static analysis tools to ease the process of finding bugs, but their results are not easy to filter out critical errors and is time consuming to analyze. To solve this problem we used two steps: first to enhance the bugs severity and second is to estimate the code quality, by Weighted Error Code Density metric. Our experiment on 10 widely used open-source Java applications automatically shows their code quality estimated using our objective metric. We also enhance the error ranking of FindBugs, and provide a clear view on the critical errors to fix as well as low priority ones to potentially ignore.
This paper develops a theoretical analysis of the tradeoff between carrier suppression and nonlin... more This paper develops a theoretical analysis of the tradeoff between carrier suppression and nonlinearities induced by optical IQ modulators in direct-detection subcarrier multiplexing systems. The tradeoff is obtained by examining the influence of the bias conditions of the modulator on the transmitted single side band signal. The frequency components in the electric field and the associated photocurrent at the output of the IQ modulator are derived mathematically. For any frequency plan, the optimum bias point can be identified by calculating the sensitivity gain for every subchannel. A setup composed of subcarriers located at multiples of the data rate ensures that the effects of intermodulation distortion are studied in the most suitable conditions. Experimental tests with up to five QPSK electrical subchannels are performed to verify the mathematical model and validate the predicted gains in sensitivity.
Modern computer applications, especially at enterprise-level, are commonly deployed with a big nu... more Modern computer applications, especially at enterprise-level, are commonly deployed with a big number of clustered instances to achieve a higher system performance, in which case single machine based solutions are less cost-effective. However, how to effectively manage these clustered applications has become a new challenge. A common approach is to deploy a front-end load balancer to optimise the workload distribution between each clustered application. Since then, many research efforts have been carried out to study effective load balancing algorithms which can control the workload based on various resource usages such as CPU and memory. The aim of this paper is to propose a new load balancing approach to improve the overall distributed system performance by avoiding potential performance impacts caused by Major Java Garbage Collection. The experimental results have shown that the proposed load balancing algorithm can achieve a significant higher throughput and lower response time compared to the round-robin approach. In addition, the proposed solution only has a small overhead introduced to the distributed system, where unused resources are available to enable other load balancing algorithms together to achieve a better system performance.
Automatic, load-independent detection of performance regressions by transaction profiles
ABSTRACT Performance regression testing is an important step in the production process of enterpr... more ABSTRACT Performance regression testing is an important step in the production process of enterprise applications. Yet, analysing this type of testing data is mainly conducted manually and depends on the load applied during the test. To ease such a manual task we present an automated, load-independent technique to detect performance regression anomalies based on the analysis of performance testing data using a concept known as Transaction Profile. The approach can be automated and it utilises data already available to the performance testing along with the queueing network model of the testing system. The presented ``Transaction Profile Run Report'' was able to automatically catch performance regression anomalies ca-used by software changes and isolate them from those caused by load variations with a precision of 80% in a case study conducted against an open source application. Hence, by deploying our system, the testing teams are able to detect performance regression anomalies by avoiding the manual approach and eliminating the need to do extra runs with varying load.
The seamless handover of streamed video in a WLAN with UDP as the transport layer is considered. ... more 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.
A recently standardized transport protocol -SCTP and the Mobile IP standard for IPv4 are examined... more A recently standardized transport protocol -SCTP and the Mobile IP standard for IPv4 are examined. Both these protocols have been suggested as offering some additional functionality to mobile users over and above that which is currently available from TCP/IP. Here, the interaction of these two new protocols is investigated through the examination of traffic flows through a number of network topologies. The results seem to suggest that although these protocols do work together, they do not currently provide all the functionality that a mobile user might desire. In particular, some limitations caused by implementations are highlighted that could be remedied by small modifications without the need to change either standard specification.
The characterisation and large-signal modelling of InGaAs pseudomorphic high electron mobility transistors
... Department of Electonic and Electrical Engineenng University College Dublin, Dublin 4, Irelan... more ... Department of Electonic and Electrical Engineenng University College Dublin, Dublin 4, Ireland Tel: +353-1-706 1908;Fax: +353-1-2830921; E-mail: [email protected] RaSa ... (3) Vgst =g5-VTO +'yt s where VIDis the pinch-off voltage and a; (3, & A, p are model parameters. ...
It is likely that an ensemble of overlapping heterogeneous wireless networks will be required to ... more 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.
Fifth IEE International Conference on 3G Mobile Communication Technologies (3G 2004) The Premier Technical Conference for 3G and Beyond, 2004
The delay characteristics of small IP packets in cellular data networks is investigated through t... more 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 traffic such as Voice over IP packets.
International Journal of Human-computer Studies / International Journal of Man-machine Studies, 2006
In general, video quality adaptation and video quality evaluation are distinct activities. Most a... more 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
The combination of increased data rates in 4G cellular networks (such as LTE Advanced), dedicated... more The combination of increased data rates in 4G cellular networks (such as LTE Advanced), dedicated multicast/broadcast services (e-MBMS) and the emergence of scalable video coding standards (H. 264 SVC) allow mobile operators to offer multimedia-...
A recently standardized transport protocol - SCTP and the Mobile IP standard for IPv4 are examine... more A recently standardized transport protocol - SCTP and the Mobile IP standard for IPv4 are examined. Both these protocols have been suggested as offering some additional functionality to mobile users over and above that which is currently available from TCP/IP. Here, the interaction of these two new protocols is investigated through the examination of traffic flows through a number of
2008 Conference on Lasers and Electro-Optics, 2008
Authors present a cost efficient narrow linewidth laser transmitter for future coherent detection... more Authors present a cost efficient narrow linewidth laser transmitter for future coherent detection systems. The spectral purity of the laser allows the phase modulation of data signals at bit rates as low as 155 Mb/s.
Ethernet Passive Optical Networks (EPONs) have attracted considerable attention from industry as ... more Ethernet Passive Optical Networks (EPONs) have attracted considerable 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 centralized environment can deliver good performance in terms of average and maximum packet delay. In this paper two new algorithms are introduced that target SLAaware EPONs and provide a good protection of offered quality of service against interference from other sources.
Bugs in a project, at any stage of Software life cycle development are costly and difficult to fi... more Bugs in a project, at any stage of Software life cycle development are costly and difficult to find and fix. Moreover, the later a bug is found, the more expensive it is to fix. There are static analysis tools to ease the process of finding bugs, but their results are not easy to filter out critical errors and is time consuming to analyze. To solve this problem we used two steps: first to enhance the bugs severity and second is to estimate the code quality, by Weighted Error Code Density metric. Our experiment on 10 widely used open-source Java applications automatically shows their code quality estimated using our objective metric. We also enhance the error ranking of FindBugs, and provide a clear view on the critical errors to fix as well as low priority ones to potentially ignore.
This paper develops a theoretical analysis of the tradeoff between carrier suppression and nonlin... more This paper develops a theoretical analysis of the tradeoff between carrier suppression and nonlinearities induced by optical IQ modulators in direct-detection subcarrier multiplexing systems. The tradeoff is obtained by examining the influence of the bias conditions of the modulator on the transmitted single side band signal. The frequency components in the electric field and the associated photocurrent at the output of the IQ modulator are derived mathematically. For any frequency plan, the optimum bias point can be identified by calculating the sensitivity gain for every subchannel. A setup composed of subcarriers located at multiples of the data rate ensures that the effects of intermodulation distortion are studied in the most suitable conditions. Experimental tests with up to five QPSK electrical subchannels are performed to verify the mathematical model and validate the predicted gains in sensitivity.
Modern computer applications, especially at enterprise-level, are commonly deployed with a big nu... more Modern computer applications, especially at enterprise-level, are commonly deployed with a big number of clustered instances to achieve a higher system performance, in which case single machine based solutions are less cost-effective. However, how to effectively manage these clustered applications has become a new challenge. A common approach is to deploy a front-end load balancer to optimise the workload distribution between each clustered application. Since then, many research efforts have been carried out to study effective load balancing algorithms which can control the workload based on various resource usages such as CPU and memory. The aim of this paper is to propose a new load balancing approach to improve the overall distributed system performance by avoiding potential performance impacts caused by Major Java Garbage Collection. The experimental results have shown that the proposed load balancing algorithm can achieve a significant higher throughput and lower response time compared to the round-robin approach. In addition, the proposed solution only has a small overhead introduced to the distributed system, where unused resources are available to enable other load balancing algorithms together to achieve a better system performance.
Automatic, load-independent detection of performance regressions by transaction profiles
ABSTRACT Performance regression testing is an important step in the production process of enterpr... more ABSTRACT Performance regression testing is an important step in the production process of enterprise applications. Yet, analysing this type of testing data is mainly conducted manually and depends on the load applied during the test. To ease such a manual task we present an automated, load-independent technique to detect performance regression anomalies based on the analysis of performance testing data using a concept known as Transaction Profile. The approach can be automated and it utilises data already available to the performance testing along with the queueing network model of the testing system. The presented ``Transaction Profile Run Report'' was able to automatically catch performance regression anomalies ca-used by software changes and isolate them from those caused by load variations with a precision of 80% in a case study conducted against an open source application. Hence, by deploying our system, the testing teams are able to detect performance regression anomalies by avoiding the manual approach and eliminating the need to do extra runs with varying load.
Uploads
Papers by Philip Perry