David Erman

The effects of Packet Delay Variation on the perceptual quality of video

The satisfaction of end-users is important when evaluating services and products. Visualizing the network behavior in mobile streaming as well as modeling the correlation between Quality of Service (QoS) and Quality of Experience (QoE) is expected to improve user satisfaction of services on the Internet. Given that network and human factors are the elements that affect the final output of the measurements, it is important to take the Packet Delay Variation (PDV) into consideration. In this paper we observe the PDV during a series of real-life experiments on a 3rd Generation (3G) network while streaming videos. User Rating (UR) values from user input are recorded accordingly. With this aim, we implemented a QoE assessment tool that measures network metrics in kernel space, while simultaneously logging user ratings with regards to the perception of an ongoing realtime video on an Android phone. The primary goal is to identify a clear trend in the QoE modeling, so that we can assess the satisfaction of a user by deriving the QoE from measurable QoS metrics. We find that PDV degrades user perception. Observations show that, during the experiments, sudden breaks and restarts in the packet flow exist. Even though the use of Exponentially Weighted Moving Average (EWMA) assists in finding a model that shows the relationship between PDV and UR, on-off flushing is a major threat affecting this relationship. The results show that correlations with different quality can be reached with various modifications of the proposed matching model.

A Survey of Reliable Multicast Communication

The paper reports on recent developments and challenges in reliable multicast communication, with special focus on reliable multicast communication at the application layer. The foundation of reliable multicast communication is given by several components, which are multicast communication, congestion control and error control. Our paper is providing a survey of these mechanisms in multicast environments.

BitTorrent Traffic Characteristics

This paper reports on a measurement and modeling study of session and message characteristics of BitTorrent traffic. BitTorrent is a peer-to-peer (P2P) replication and distribution system developed as an alternative to the classical client-server model to reduce the load on content servers and networks. Results are reported on measurement, modeling and analysis of application and link layer traces collected at the Blekinge Institute of Technology (BTH) and a local ISP in Sweden. Link layer traces and application logs were collected, modeled and analyzed using a dedicated measurement infrastructure developed at BTH to collect P2P traffic. New results are reported on important session and message characteristics of BitTorrent, i.e., session inter arrivals, sizes and durations, request rates and response times. Our results show that session interarrivals can be accurately modeled by a second-order hyper-exponential distribution while session durations and sizes can be reasonably well modeled by various mixtures of the log-normal and Weibull distributions. Response times have been observed to be modeled by a dual log-normal mixture, while request rates are modeled as dual Gaussian distributions

A middleware framework for communication in cognitive radio networks

Cognitive radio networks are expected to address and resolve important operational challenges such as opportunistic spectrum access, spectrum and network heterogeneities and requests for the provision of diverse Quality-of-Service (QoS) for different applications. Accordingly, a number of network functionalities are required to take into account these challenges towards the efficient management of cognitive radio networks. This paper advances a new architecture for the management of cognitive radio networks. The architecture is designed and developed at the application layer and incorporates sensing and prediction, addressing and routing, middleware and decision making. Accordingly, a number of management functions are required to address the challenges associated with the management of cognitive radio networks. The paper provides an analysis of these components as well.

Providing an User Centric Always Best Connection

Although Quality of Experience (QoE) is perceived as a subjective measure of a user’s experience, it is the only measure that actually counts to a user of a service. It is essential to identify, quantify and ultimately improve the perception of QoE for a user. The PERIMETER project improves the user’s experience by identifying a more user-centric network selection, based on QoE calculations and user preferences. PERIMETER defines a generic QoE model which forms the basis for QoE signalling and QoE based content adaptation support. This paper provides an insight into how user centric seamless mobility is being achieved by PERIMETER, beginning with an explanation of QoE and the need for preferences. Next, more details of the complete system, including QoE management, user feedback and the final delivery, are provided. Finally, an outlook is given on PERIMETER’s future plans and its contributions to research in the Future Internet.

Performance of cognitive radio spectrum access with intra- and inter-handoff

Opportunistic spectrum access (OSA) is a technology that allows unlicensed users to access spectrum holes and to provide so efficient use of radio resources. Most studies done on OSA focus on the situation when the unlicensed user performs the spectrum handoff only within a single cognitive radio network (so-called intra-handoff). In this paper, we consider the users (licensed or unlicensed) to be able to do inter-handoff among different cognitive radio cells as well. The cells provide priority to inter-handoff users. By considering multiple cells being in steady-state and showing identical statistics, the arrival rates of inter-handoff users are determined. We study the OSA performance of unlicensed users under both intra- and inter-handoff schemes, with respect to the blocking and forced-termination probabilities of unlicensed users as well as the unlicensed user service-completion and inter-handoff throughputs. Our Markov chain based numerical analysis is validated by simulation experiments.

Simulation and analysis of a combined mobility model with obstacles

The use of simulations has become increasingly frequent in the study and the performance evaluation of network systems. The simulation environment deeply influences the behaviour of results, so a model that simulates a realistic movement of the nodes is necessary for the study of wireless networks. Simple mobility models do not provide realistic scenarios. Often movements are completely random, uncorrelated and in open space, without the chance of considering the effects of obstacles or rules that limit and guide the movement. In this paper, we propose a more realistic mobility model, studied for indoor environments (but applicable to outdoor models as well). Given the map of the obstacles in the simulation area (e.g. a floor plan), the nodes have the possibility to move in random walk just avoiding to cross the obstacles (e.g. walls), or following a specified virtual path that connects all the simulation area, or a hybrid of the two. Our tool creates a file containing the movement of the nodes during the whole simulation time. Simulation results show that nodes are highly dependent on the different obstacles maps and pathways. Furthermore, a mathematical demonstration is given to validate the results obtained by simulation in a simple case.

Validating BitTorrent models

BitTorrent (bt), a Peer-to-Peer (p2p) distribution system, is a major bandwidth consumer in the current Internet. This paper reports on a measurement study of bt traffic intended to identify potential traffic invariants. To this end, we employ high-accuracy packet capture hardware together with specialized parsing software. Important characteristics regarding bt sessions and messages as well as general system characteristics are reported.The results indicate that characteristics such as session inter-arrival times are corroborated to be exponentially distributed, while other characteristics are shown to differ from previously reported results. These differences are attributed to changes in the core bt algorithms. Further, it is observed that long- and heavy-tailed distributions can be used to model several characteristics. The log-normal, Pareto and mixtures of these distributions are used to model session sizes and durations, while the Weibull distribution has been observed to model message inter-arrival and inter-departure times for bandwidth-limited clients.

Transfer Rate Models for Gnutella Signaling Traffic

This paper reports on transfer rate models for the Gnutella signaling protocol. New results on message-level and IP-level rates are presented. The models are based on traffic captured at the Blekinge Institute of Technology (BTH) campus in Sweden and offer several levels of granularity: message type, application layer and network layer. The aim is to obtain parsimonous models suitable for analysis and simulation of P2P workload.

An application layer architecture for seamless roaming

The paper advances a new architecture for seamless roaming, which is implemented at the application layer. This architecture is subject for the research projects PERIMETER and MOBICOME, recently granted by the EU STREP FP7 and EUREKA, respectively. The research challenges are on mobility management, security, QoE management, overlay routing, node positioning, mobility modeling and prediction, middleware and handover. The foundation of seamless handover is provided by several components, the most important ones being the handover, mobility management, connectivity management and Internet mobility. The paper provides an analysis of these components as well.