Traffic Control and Quality of Service in Wireless LANs

The thesis deals with two aspects of the IEEE 802.11 standard. The first is the so-called “performance anomaly”: the variable bandwidth of the links and the use of multiple transmission rates push the throughput of all stations to align to the slowest one. To tackle this problem we designed and developed a simple channel-aware scheduling algorithm, called DTT, which actualises the proportional fairness concept, thus leading to noteworthy improvements, and in particular to flow isolation. This is achieved by measuring link quality as the time needed to deliver a frame. The resource to share is no longer capacity, but the time the channel is in use. DTT has then been integrated into a prototype Access Point, which is the first working implementation of a scheduler based on proportional fairness. Secondly, we focused on 802.11e networks, which, though enhancing QoS support, still offer scarce reliability of QoS guarantees and suffer from network congestion. We devised two admission control algorithms to assess the maximum number of users allowable to the services while satisfying QoS requirements. Following the studies on DTT, both algorithms centre the admission test on the time occupancy of the medium. The first algorithm builds on an analytical model of the EDCA mode in non-saturation conditions. This closely matches the real behaviour of a network carrying time-sensitive applications, thus overcoming the limits of all previous works, based on saturation models. The second algorithm uses and extends to 802.11e the NUC, a parameter defined and proved effective for 802.11b systems. This scheme needs measures of the actual state of the network. Simulations run within the E-model framework show good accuracy performance for both models

Investigation of quality of services (QoS) support for real-time or mission critical services over IEEE 802.11e wireless networks.

Multimedia application is currently making much impact in this technological era. It has been thekey driving force behind the convergence of fixed, mobile and IP networks. Furthermore, real-timeapplications are making head way in vehicular networks, mission critical applications which usededicated short range communications (DSRC). 802.l i e standards support quality of services(QoS) guarantees in these applications. This is opposed to the problem with 802.11 legacy whichis based on distributed coordination function (DCF), and its inability to prioritized applications forservice differentiation. Simulation was done on various 802.l i e networks which use enhancedDCF (EDCF). In these simulations, it was observed that controlling low priority applicationsenhances the effectiveness of high priority applications. Different MAC and traffic generationparameters were used in various scenarios. It was actually observed that high priority applicationshave greater impacts on the performance of the network and hence performs better when itcomes to delay and throughput requirements. Even when the number of high priority applicationswere reduced, the results obtained was still able to satisfy QoS requirements for each traffic type.Results for different scenarios were taken and discussed. Also, differentiated values of delay,throughput and packet loss were recorded when same and different values of MAC and trafficgeneration parameters were used. In all results the International Telecommunications Union (ITU-T) values of these metrics parameters were kept low. These make the network design suitable forroad safety application where very low delay is required for emergency messages and tolerabledelay in routine messages. The results obtained show th at, this network can be applicable inroad safety, simply because of the low delay, and low loss which implies , messages to cars canbe successfully delivered and also good throughput. 802.11 legacy standard lacks servicedifferentiation that limits QoS support for real-time applications. These simulations were able tohandle the drawback associated with this standard and prefer a better standard which is 802.l i ethat provides differentiated access to the metrics that was used in analyzing QoS in this research

Towards the Quality of Service for VoIP traffic in IEEE 802.11 Wireless Networks

The usage of voice over IP (VoIP) traffic in IEEE 802.11 wireless networks is expected to increase in the near future due to widely deployed 802.11 wireless networks and VoIP services on fixed lines. However, the quality of service (QoS) of VoIP traffic in wireless networks is still unsatisfactory. In this thesis, I identify several sources for the QoS problems of VoIP traffic in IEEE 802.11 wireless networks and propose solutions for these problems. The QoS problems discussed can be divided into three categories, namely, user mobility, VoIP capacity, and call admission control. User mobility causes network disruptions during handoffs. In order to reduce the handoff time between Access Points (APs), I propose a new handoff algorithm, Selective Scanning and Caching, which finds available APs by scanning a minimum number of channels and furthermore allows clients to perform handoffs without scanning, by caching AP information. I also describe a new architecture for the client and server side for seamless IP layer handoffs, which are caused when mobile clients change the subnet due to layer 2 handoffs. I also present two methods to improve VoIP capacity for 802.11 networks, Adaptive Priority Control (APC) and Dynamic Point Coordination Function (DPCF). APC is a new packet scheduling algorithm at the AP and improves the capacity by balancing the uplink and downlink delay of VoIP traffic, and DPCF uses a polling based protocol and minimizes the bandwidth wasted from unnecessary polling, using a dynamic polling list. Additionally, I estimated the capacity for VoIP traffic in IEEE 802.11 wireless networks via theoretical analysis, simulations, and experiments in a wireless test-bed and show how to avoid mistakes in the measurements and comparisons. Finally, to protect the QoS for existing VoIP calls while maximizing the channel utilization, I propose a novel admission control algorithm called QP-CAT (Queue size Prediction using Computation of Additional Transmission), which accurately predicts the impact of new voice calls by virtually transmitting virtual new VoIP traffic

Quality aspects of Internet telephony

Internet telephony has had a tremendous impact on how people communicate. Many now maintain contact using some form of Internet telephony. Therefore the motivation for this work has been to address the quality aspects of real-world Internet telephony for both fixed and wireless telecommunication. The focus has been on the quality aspects of voice communication, since poor quality leads often to user dissatisfaction. The scope of the work has been broad in order to address the main factors within IP-based voice communication. The first four chapters of this dissertation constitute the background material. The first chapter outlines where Internet telephony is deployed today. It also motivates the topics and techniques used in this research. The second chapter provides the background on Internet telephony including signalling, speech coding and voice Internetworking. The third chapter focuses solely on quality measures for packetised voice systems and finally the fourth chapter is devoted to the history of voice research. The appendix of this dissertation constitutes the research contributions. It includes an examination of the access network, focusing on how calls are multiplexed in wired and wireless systems. Subsequently in the wireless case, we consider how to handover calls from 802.11 networks to the cellular infrastructure. We then consider the Internet backbone where most of our work is devoted to measurements specifically for Internet telephony. The applications of these measurements have been estimating telephony arrival processes, measuring call quality, and quantifying the trend in Internet telephony quality over several years. We also consider the end systems, since they are responsible for reconstructing a voice stream given loss and delay constraints. Finally we estimate voice quality using the ITU proposal PESQ and the packet loss process. The main contribution of this work is a systematic examination of Internet telephony. We describe several methods to enable adaptable solutions for maintaining consistent voice quality. We have also found that relatively small technical changes can lead to substantial user quality improvements. A second contribution of this work is a suite of software tools designed to ascertain voice quality in IP networks. Some of these tools are in use within commercial systems today

Achieving Soft Real-time Guarantees for Interactive Applications in Wireless Mesh Networks

The use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic

Analysis and design of efficient techniques for video transmission in IEEE 802.11 wireless ad hoc networks

[EN] Wireless mobile ad ho networks, also known as MANETs, are omposed by independent mobile stations that ommuni ate without requiring any sort of infrastru ture for support. These networks are hara terized by variable bandwidth values and frequent path breaks, whi h are due to hannel noise, interferen e between stations and mobility. Su h fa tors require significant adaptation apabilites at different levels of the proto ol suites employed, enabling stations to qui kly respond to fast- hanging network onditions. Resear h on the most adequate proto- ols for the physi al, MAC and routing layers is still on-going, though some basi onsensus has already been rea hed and several testbeds have been setup around the world. To deploy real-time multimedia servi es, namely voi e and video, on top of su h an unreliable network environment is a very hallenging task. In this thesis we propose to a hieve that goal starting from urrently available Wi-Fi te hnology, and gradually finding the most adequate enhan ements to ea h proto ol layer of interest; we then ombine these enhan ements until we a hieve a omplete QoS framework for ad ho networks. By using urrently available te hnology we assure that the proposal of this thesis has an inherent high-level of appli ability on real life environments. Sin e our working field fo uses on video transmission over wireless ad ho networks, we will show how it is possible to support several QoS- onstrained video streams in MANET environments hara terized by moderate to high mobility levels, and by a significant amount of best efort traffic[ES] Las redes inalámbricas ad hoc, también conocidas como redes MANET, están compuestas por un conjunto de estaciones móviles independientes capaces de omunicarse entre sí sin necesidad de ningún tipo de infraestructura común de comunicaciones. Estas redes se caracterizan por tener un ancho de banda variable y pérdidas frecuentes de ruta que se pueden atribuir al ruido del anal inalámbrico, a la interferencia entre las estaciones móviles o bien a la movilidad de las estaciones. Dichos factores requieren una gran capacidad de adaptación en las diferentes capas de la arquitectura de protocolos, permitiendo a una estación responder rápidamente a posibles cambios bruscos en las condiciones de la red. A pesar de que aún se están realizando trabajos de investigación en bus a de los protocolos más adecuados para las capas físicas, a eso al medio (MAC) y encaminamiento, ha sido posible llegar a un nivel básico de consenso, lo cual ha permitido el despliegue de plataformas y entornos aplicados que utilizan tecnología de red MANET. Ofrecer servicios multimedia, como voz y vídeo, en redes con tan poca habilidad es un desafío importante. En esta tesis nos proponemos alcanzar este objetivo partiendo de la tecnología Wi-Fi actualmente disponible, encontrando de forma paulatina las mejoras más importantes en las diferentes capas de la arquitectura de red, para llegar, finalmente, a una solución integrada capaz de ofrecer calidad de servicio (QoS) en las redes MANET. Al utilizar la tecnología que disponemos actualmente nos aseguramos que las propuestas de esta tesis tengan un alto grado de aplicabilidad en entornos reales. Ya que la línea de trabajo de la tesis está aplicada a la transmisión de vídeo en redes MANET, demostraremos que es posible ofrecer calidad de servicio a varios flujos de vídeo en una red MANET caracterizada por altos grados de movilidad en sus nodos y un nivel significativo de tráfico o de tipo best effortTavares De Araujo Cesariny Calafate, CM. (2006). Analysis and design of efficient techniques for video transmission in IEEE 802.11 wireless ad hoc networks [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135282TESI

Bandwidth reservation in mobile ad hoc networks for providing QoS : adaptation for voice support

Le support de qualité de service (QoS) dans les réseaux MANETs (Mobile Ad-Hoc NETworks) a attiré une grande attention ces dernières années. Bien que beaucoup de travaux de recherche ont été consacré pour offrir la QoS dans les réseaux filaires et cellulaires, les solutions de QoS pour le support du trafic temps réel dans les MANET reste l'un des domaines de recherche les plus difficiles et les moins explorés. En fait, les applications temps réel telles que la voix et la vidéo ne pourrait pas fonctionner correctement dans les MANET sans l'utilisation d'un protocole de contrôle d'accès au support (MAC) orienté QoS. En effet, les trafics temps réel demandent des exigences strictes en termes de délai de transmission et de taux de perte de paquets qui peuvent être remplies uniquement si la sous-couche MAC fournit un délai d'accès au canal borné, et un faible taux de collision. Le but de cette thèse est la proposition et l'analyse d'un protocole MAC basé sur la réservation pour garantir la QoS dans les MANETs. Tout d'abord, nous étudions un problème majeur dans la réservation de ressources dans les MANETs qui est la cohérence des réservations. Notre analyse des protocoles de réservation existant pour les MANETs révèle que de nombreux conflits de réservations entre les nœuds voisins se produisent pendant la phase d'établissement de réservation. Ces conflits, qui sont principalement dues à la collision des messages de contrôle de réservation, ont un impact important sur les performances du protocole de réservation, et conduisent à un taux de collision et de perte de paquet importants pendant la durée de vie de la connexion, ce qui n'est pas acceptable pour les trafics temps réels. Nous proposons un nouveau protocole MAC basé sur la réservation qui résout ces conflits. Le principe de notre protocole est d'établir une meilleure coordination entre les nœuds voisins afin d'assurer la cohérence des réservations. Ainsi, avant de considérer qu'une réservation est réussite, le protocole s'assure que chaque message de contrôle envoyé par un nœud pour établir une réservation est bien reçu par tous ses nœuds voisins. Dans la deuxième partie de cette thèse, nous appliquons le protocole de réservation proposé au trafic de type voix. Ainsi, nous étendons ce protocole afin de prendre en compte les caractéristiques du trafic voix, tout en permettant le transport de trafic de données. Nous nous focalisons sur l'utilisation efficace de la bande passante et les mécanismes pour réduire le gaspillage de bande passante. La dernière partie de cette thèse concerne l'extension du protocole proposé en vue de réserver la bande passante pour une connexion temps réel sur un chemin. Ainsi, le protocole MAC de réservation proposé est couplé avec un protocole de routage réactif. En outre, le protocole est étendu avec des mécanismes de gestion de à mobilité afin de faire face à la dégradation des performances due à la mobilité des nœuds. Nous évaluons les performances du protocole proposé dans plusieurs scénarios dans lesquels nous montrons sa supériorité par rapport aux standards existants.QoS provisioning over Mobile Ad-Hoc Networks (MANETs) has attracted a great attention in recent years. While much research effort has been devoted to provide QoS over wired and cellular networks, QoS solutions for the support of real-time traffic over MANETs remains one of the most challenging and least explored areas. In fact, real-time applications such as voice and video could not function properly on MANETs without a QoS oriented medium access control (MAC) scheme. Indeed, real-time traffics claim strict requirements in terms of transmission delay and packet dropping that can be fulfilled only if the MAC sub-layer provides bounded channel access delay, and low collision rate. The purpose of this thesis is the proposal and analysis of an efficient reservation MAC protocol to provide QoS support over MANETs. Firstly, we study one major issue in resource reservation for MANETs which is reservation consistency. Our analysis of existing reservation MAC protocols for MANETs reveals that many reservation conflicts between neighbor nodes occur during the reservation establishment phase. These conflicts which are mainly due to collisions of reservation control messages, have an important impact on the performance of the reservation protocol, and lead to a significant collision and loss of packets during the life-time of the connection, which is not acceptable for real-time traffics. We design a new reservation MAC protocol that resolves these conflicts. The main principle of our protocol is to achieve better coordination between neighbor nodes in order to ensure consistency of reservations. Thus, before considering a reservation as successful, the protocol tries to ensure that each reservation control message transmitted by a node is successfully received by all its neighbors. In the second part of this thesis, we apply the proposed reservation protocol to voice traffic. Thus, we extend this protocol in order to take into account the characteristics of voice traffic, while enabling data traffic. We focus on efficient bandwidth utilization and mechanisms to reduce the waste of bandwidth. The last part of this thesis relates to the extension of the proposed protocol in order to reserve resources for a real-time connection along a path. Thus, the proposed reservation MAC protocol is coupled with a reactive routing protocol. In addition, the protocol is extended with mobility handling mechanisms in order to cope with performance degradation due to mobility of nodes. We evaluate the performance of the proposed scheme in several scenarios where we show its superiority compared to existing standards

LTE Optimization and Resource Management in Wireless Heterogeneous Networks

Mobile communication technology is evolving with a great pace. The development of the Long Term Evolution (LTE) mobile system by 3GPP is one of the milestones in this direction. This work highlights a few areas in the LTE radio access network where the proposed innovative mechanisms can substantially improve overall LTE system performance. In order to further extend the capacity of LTE networks, an integration with the non-3GPP networks (e.g., WLAN, WiMAX etc.) is also proposed in this work. Moreover, it is discussed how bandwidth resources should be managed in such heterogeneous networks. The work has purposed a comprehensive system architecture as an overlay of the 3GPP defined SAE architecture, effective resource management mechanisms as well as a Linear Programming based analytical solution for the optimal network resource allocation problem. In addition, alternative computationally efficient heuristic based algorithms have also been designed to achieve near-optimal performance