Greediness control algorithm for multimedia streaming in wireless local area networks

This work investigates the interaction between the application and transport layers while streaming multimedia in a residential Wireless Local Area Network (WLAN). Inconsistencies have been identified that can have a severe impact on the Quality of Experience (QoE) experienced by end users. This problem arises as a result of the streaming processes reliance on rate adaptation engines based on congestion avoidance mechanisms, that try to obtain as much bandwidth as possible from the limited network resources. These upper transport layer mechanisms have no knowledge of the media which they are carrying and as a result treat all traffic equally. This lack of knowledge of the media carried and the characteristics of the target devices results in fair bandwidth distribution at the transport layer but creates unfairness at the application layer. This unfairness mostly affects user perceived quality when streaming high quality multimedia. Essentially, bandwidth that is distributed fairly between competing video streams at the transport layer results in unfair application layer video quality distribution. Therefore, there is a need to allow application layer streaming solutions, tune the aggressiveness of transport layer congestion control mechanisms, in order to create application layer QoE fairness between competing media streams, by taking their device characteristics into account. This thesis proposes the Greediness Control Algorithm (GCA), an upper transport layer mechanism that eliminates quality inconsistencies caused by rate / congestion control mechanisms while streaming multimedia in wireless networks. GCA extends an existing solution (i.e. TCP Friendly Rate Control (TFRC)) by introducing two parameters that allow the streaming application to tune the aggressiveness of the rate estimation and as a result, introduce fair distribution of quality at the application layer. The thesis shows that this rate adaptation technique, combined with a scalable video format allows increased overall system QoE. Extensive simulation analysis demonstrate that this form of rate adaptation increases the overall user QoE achieved via a number of devices operating within the same home WLAN

Wireless Efficiency Versus Net Neutrality

Symposium: Rough Consensus and Running Code: Integrating Engineering Principles into Internet Policy Debates, held at the University of Pennsylvania\u27s Center for Technology Innovation and Competition on May 6-7, 2010. This Article first addresses congestion and congestion control in the Internet. It shows how congestion control has always depended upon altruistic behavior by end users. Equipment failures, malicious acts, or abandonment of altruistic behavior can lead to severe congestion within the Internet. Consumers benefit when network operators are able to control such congestion. One tool for controlling such congestion is giving higher priority to some applications, such as telephone calls, and giving lower priority or blocking other applications, such as file sharing. The Article then turns to wireless networks and shows that in addition to congestion issues, priority routing in wireless can make available capacity that would otherwise go unused. Wireless systems that are aware of the application being carried in each packet can deliver more value to consumers than can dumb networks that treat all packets identically. Handsets are both complements to and substitutes for the network infrastructure of wireless networks and any analysis of handset bundling should consider this complementarity. Next, the Article reviews analogous issues in electrical power and satellite communications and shows how various forms of priority are used to increase the total value delivered to consumers by these systems. Finally, the Article observes that regulations that prohibit priority routing of packets and flows on the Internet will create incentives to operate multiple networks

Support infrastructures for multimedia services with guaranteed continuity and QoS

Advances in wireless networking and content delivery systems are enabling new challenging provisioning scenarios where a growing number of users access multimedia services, e.g., audio/video streaming, while moving among different points of attachment to the Internet, possibly with different connectivity technologies, e.g., Wi-Fi, Bluetooth, and cellular 3G. That calls for novel middlewares capable of dynamically personalizing service provisioning to the characteristics of client environments, in particular to discontinuities in wireless resource availability due to handoffs. This dissertation proposes a novel middleware solution, called MUM, that performs effective and context-aware handoff management to transparently avoid service interruptions during both horizontal and vertical handoffs. To achieve the goal, MUM exploits the full visibility of wireless connections available in client localities and their handoff implementations (handoff awareness), of service quality requirements and handoff-related quality degradations (QoS awareness), and of network topology and resources available in current/future localities (location awareness). The design and implementation of the all main MUM components along with extensive on the field trials of the realized middleware architecture confirmed the validity of the proposed full context-aware handoff management approach. In particular, the reported experimental results demonstrate that MUM can effectively maintain service continuity for a wide range of different multimedia services by exploiting handoff prediction mechanisms, adaptive buffering and pre-fetching techniques, and proactive re-addressing/re-binding

Adaptation of the IEEE 802.11 protocol for inter-satellite links in LEO satellite networks

Knowledge of the coefficient of thermal expansion (CTE) of a ceramic material is important in many application areas. Whilst the CTE can be measured, it would be useful to be able to predict the expansion behaviour of multiphase materials.. There are several models for the CTE, however, most require a knowledge of the elastic properties of the constituent phases and do not take account ofthe microstructural features of the material. If the CTE could be predicted on the basis of microstructural information, this would then lead to the ability to engineer the microstructure of multiphase ceramic materials to produce acceptable thermal expansion behaviour. To investigate this possibility, magnesia-magnesium aluminate sp~el (MMAS) composites, consisting of a magnesia matrix and magnesium aluminate s~ne'l (MAS) particles, were studied. Having determined a procedure to produce MAS fr alumina and magnesia, via solid state sintering, magnesia-rich compositions wit ~ various magnesia contents were prepared to make the MMAS composites. Further, the l\.1MAS composites prepared from different powders (i.e. from an alumina-magnesia mixture ahd from a magnesia-spinel powder) were compared. Com starch was added into the powder mixtures before sintering to make porous microstructures. Microstructural development and thermal expansion behaviour ofthe MMAS composites were investigated. Microstructures of the MAS and the MMAS composites as well as their porous bodies were quaritified from backscattered electron micrographs in terms of the connectivity of solids i.e. solid contiguity by means of linear intercept counting. Solid contiguity decreased with increasing pore content and varied with pore size, pore shape and pore distribution whereas the phase contiguity depended strongly on the chemical composition and was less influenced by porosity. ' The thermal expansion behaviour of the MAS and the MMAS composites between 100 and 1000 °C was determined experimentally. Variation in the CTE ofthe MAS relates to the degree of spinel formation while the thermal expansion of the MMAS composites depends strongly on phase content. However, the MMAS composites with similar phase compositions but made from different manufacturing processes showed differences in microstructural features and thermal expansion behaviour. Predictions of the CTE values for composites based on a simple rule-of-mixtures (ROM) using volume fraction were compared with the measured data. A conventional ROM accurately predicted the effective CTE of a range of dense alumina-silicon carbide particulate composites but was not very accurate for porous multiphase structures. It provided an upper bound prediction as all experimental values were lower. Hence, the conventional ROM was modified to take account of quantitative microstructural parameters obtained from solid contiguity. The modified ROM predicted lower values and gave a good agreement with the experimental data. Thus, it has been shown that quantitative microstructural information can be used to predict the CTE of multiphase ceramic materials with complex microstructures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Interaktive latenzkritische Anwendungen in mobilen Ad-hoc Netzen

In this thesis we discuss the challenges that latency-sensitive interactive applications face in mobile ad-hoc networks. By using multi-player games as an example, we argue that the traditional client-server architecture is unsuitable for this new environment. We consequently create a novel communication architecture as well as quality of service mechanisms that can support the network requirements of such applications in mobile environments. By using a number of distributed zone servers that are selected and managed dynamically by our server selection algorithm, we provide a scalable approach that offers the necessary redundancy. Furthermore, we propose additional quality of service mechanisms to reduce latency and packet loss for interactive applications. We evaluate our approach through network simulation and realistic mobile gaming scenarios. The performance of our evaluation is checked against real-world measurements.In dieser Arbeit werden die Probleme und Herausforderungen von latenz-kritischen interactiven Computeranwendungen in mobilen Ad-hoc Netzen untersucht. Am Beispiel von Mehrbenutzercomputerspielen zeigen wir, dass traditionelle Client-Server Architekturen für diese neuen Umgebungen ungeeignet sind. Im Rahmen dieser Arbeit wird daher eine neue Kommunikationsarchitektur sowie verschiedene Mechanismen zur Erhöhung der Dienstgüte vorgeschlagen. Mit Hilfe von Zonenserver, die durch den Serverauswahlalgorithmus ausgesucht und verwaltet werden zeigen wir einen Ansatz auf, der sowohl bezüglich der Netzgröße skalierbar ist als auch die notwendige Redundanz bereitstellt. Wir zeigen die Funktionalität und die Leistung unseres Ansatzes mit Hilfe von Netzsimulationen bei denen realistische Szenarien für mobiles Spielen simuliert werden. Der hierbei benutze Netzsimulator wurde dafür auf Basis von eigenen Messungen verbessert und für das jeweilige Szenario passend eingestellt