Saturation Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a saturation throughput analysis of the IEEE 802.11 protocol at the data link layer by including the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture effects, specially in an environment of high interference, become important in terms of the actual observed throughput. As far as the 4-way handshaking mechanism is concerned, we extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel. This way, any channel model characterizing the physical transmission medium can be accommodated, including AWGN and fading channels. We also extend the Markov model in order to consider the behavior of the contention window when employing the basic 2-way handshaking mechanism. Under the usual assumptions regarding the traffic generated per node and independence of packet collisions, we solve for the stationary probabilities of the Markov chain and develop expressions for the saturation throughput as a function of the number of terminals, packet sizes, raw channel error rates, capture probability, and other key system parameters. The theoretical derivations are then compared to simulation results confirming the effectiveness of the proposed models.Comment: To appear on IEEE Transactions on Communications, 200

Unsaturated Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a throughput analysis of the IEEE 802.11 protocol at the data link layer in non-saturated traffic conditions taking into account the impact of both transmission channel and capture effects in Rayleigh fading environment. The impact of both non-ideal channel and capture become important in terms of the actual observed throughput in typical network conditions whereby traffic is mainly unsaturated, especially in an environment of high interference. We extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel, along with a state characterizing the system when there are no packets to be transmitted in the buffer of a station. Finally, we derive a linear model of the throughput along with its interval of validity. Simulation results closely match the theoretical derivations confirming the effectiveness of the proposed model.Comment: To appear on IEEE Transactions on Wireless Communications, 200

A flexible QoS-aware routing protocol for infrastructure-less B3G networks

International audienceCurrent mobile devices support multiple network technolo- gies and network composition via such devices can enable service provisioning across heterogeneous networks. One of the key challenges for realizing this view is inter-domain routing. Indeed, given the diversity of involved network technologies and infrastructures, a exible routing protocol that takes into account their quality properties and dynam- ics is an important requirement. In this paper, we present a exible quality-aware routing protocol for infrastructure-less B3G environments that enables discovery of routes with op- timal bandwidth, delay or cost according to the preference of each client. The protocol is based on the Optimized Link- State Routing (OLSR) protocol and is designed to enable computation of quality-aware routes in multi-network envi- ronments. We detail the protocol, discuss its deployment and provide experimental results

Implementation and Performance Evaluation of an NGN prototype using WiMax as an Access Technology

Telecommunications networks have evolved to IP-based networks, commonly known as Next Generation Networks (NGN). The biggest challenge in providing high quality realtime multimedia applications is achieving a Quality of Service (QoS) consistent with user expectations. One of the key additional factors affecting QoS is the existence of different QoS mechanisms on the heterogeneous technologies used on NGN platforms. This research investigates the techniques used to achieve consistent QoS on network technologies that use different QoS techniques. Numerous proposals for solving the end-to-end QoS problem in IP networks have adopted policy-based management, use of signalling protocols for communicating applications QoS requirements across different Network Elements and QoS provisioning in Network Elements. Such solutions are dependent on the use of traffic classification and knowledge of the QoS requirements of applications and services on the networks. This research identifies the practical difficulties involved in meeting the QoS requirements of network traffic between WiMax and an IP core network. In the work, a solution based on the concept of class-of-service mapping is proposed. In the proposed solution, QoS is implemented on the two networks and the concept of class-of-service mapping is used to integrate the two QoS systems. This essentially provides consistent QoS to applications as they traverse the two network domains and hence meet end-user QoS expectations. The work is evaluated through a NGN prototype to determine the capabilities of the networks to deliver real-time media that meets user expectations

CORDENA : uma plataforma para gestão de redes baseada em políticas : arquitecturas e mecanismos de tradução de políticas

O alargamento das redes, o aumento da sua complexidade e a heterogeneidade dos equipamentos a elas ligados têm dificultado de uma forma geral a sua gestão e monitorização. Garantir uma determinada qualidade de serviço fim-a-fim, ou disponibilizar de uma forma controlada serviços de valor para suportar processos de negócio críticos, são objectivos complexos a que a área da gestão de redes tem tentado dar resposta. O presente trabalho propõe uma plataforma para Gestão de Redes Baseada em Políticas – A Plataforma CORDENA e uma forma escalável de transposição de políticas para a rede ao nível do repositório de políticas como forma de minimizar os impactos em termos de desempenho e escalabilidade. O enfoque principal vai para a modelação mecânica e lógica da arquitectura, para a estrutura do modelo de informação subjacente, e para os mecanismos internos de tradução, responsáveis por transcrever entidades organizacionais em propriedades da infra-estrutura. São tecidos alguns exemplos de aplicação como forma de elucidar acerca das vantagens no uso de uma implementação com base nos princípios e mecanismos aqui descritos. É também descrito o ambiente laboratorial virtual com o qual foram testadas diversas tecnologias no decurso dos trabalhos inerentes à investigação associada. Estas incursões técnicas foram incluídas como uma mais valia e uma abordagem interessante para o desenvolvimento, teste e aplicação de políticas em rede que esta dissertação não quis deixar de registar. É ainda apresentado um conjunto de considerações colhidas no decurso das experimentações efectuadas e no desenho da arquitectura propriamente dita, assim como uma proposta de planeamento. O trabalho realça ainda alguns trabalhos de investigação, mantendo uma linha de continuidade caracterizada pela criação de redes inteligentes ou auto suficientes, nomeadamente o uso de meta-políticas como complemento ao modelo aqui apresentado.The growth of communication networks, their increasing complexity and the heterogeneity of the connected equipments, are making the administration and monitoring tasks difficult to accomplish. Providing a specific Quality of Service from an end-to-end view, or delivering value added services in a controlled way to support critical business processes, are becoming complex goals for which the network management tries to get the right answers. The present work proposes a framework for Policy Based Network Management - The Framework CORDENA, along with a scalable solution for policy translation from the high business level to the network layer. This is carried out at the repository level in order to minimize the performance impact and to maintain the architecture more scalable. The main focus is given to the mechanical and logical modeling of the architecture, for the underlying information model structures, and for the internal mechanisms which translate the business objects into infrastructure properties. In order to understand to what extent the principles and the mechanisms described here can be useful in a real live environment, some application examples are provided. The test laboratory environment used for the technology research and experimentation is also described since it brings a added value contribution for polices development and testing. In addition, it is presented an implementation plan and some considerations collected throughout the work in designing and modelling the CORDENA framework. Finally, this work also highlights some research initiatives that complement the scope regarding the Intelligent Networks research area, namely the meta-policies approach

Recent Advances in Wireless Communications and Networks

This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters