Adaptive fair channel allocation for QoS enhancement in IEEE 802.11 wireless LANs

The emerging widespread use of real-time multimedia applications over wireless networks makes the support of quality of service (QoS) a key problem. In this paper, we focus on QoS support mechanisms for IEEE 802.11 wireless ad-hoc networks. First, we review limitations of the upcoming IEEE 802.11e enhanced DCF (EDCF) and other enhanced MAC schemes that have been proposed to support QoS for 802.11 ad-hoc networks. Then, we describe a new scheme called adaptive fair EDCF that extends EDCF, by increasing the contention window during deferring periods when the channel is busy, and by using an adaptive fast backoff mechanism when the channel is idle. Our scheme computes an adaptive backoff threshold for each priority level by taking into account the channel load. The new scheme significantly improves the quality of multimedia applications. Moreover, it increases the overall throughput obtained both in medium and high load cases. Simulution results show that our new scheme outperforms EDCF and other enhanced schemes. Finally, we show that the adaptive fair EDCF scheme achieves a high degree of fairness among applications of the same priority level

Métrologie pour l'analyse comparative des performances temporelles des liens Bluetooth

Cet article présente une étude métrologique des performances temporelles de la technologie de réseau sans fil Bluetooth. Cette étude est réalisée en collaboration avec le Centre Commun de Recherche d'EADS dans le but de connaître précisément le temps d'acheminement d'une donnée quelconque par le réseau Bluetooth. Les caractéristiques essentielles de Bluetooth ayant une forte incidence sur les performances temporelles sont présentées dans une première partie. Dans un second temps, l'étude métrologique est détaillée, du mode opératoire à la présentation des résultats. L'analyse de ces derniers montre que cette technologie présente des performances intéressantes sur le plan temporel, notamment dans son mode de transmission synchrone

FHCF: A simple and efficient scheduling scheme for IEEE 802.11e wireless networks

The IEEE 802.11e medium access control (MAC) layer protocol is an emerging standard to support quality of service (QoS) in 802.11 wireless networks. Some recent works show that the 802.11e hybrid coordination function (HCF) can improve signi¯cantly the QoS support in 802.11 networks. A simple HCF referenced scheduler has been proposed in the 802.11e which takes into account the QoS requirements of °ows and allocates time to stations on the basis of the mean sending rate. As we show in this paper, this HCF referenced scheduling algorithm is only e±cient and works well for °ows with strict constant bit rate (CBR) characteristics. However, a lot of real-time applications, such as videoconferencing, have some variations in their packet sizes, sending rates or even have variable bit rate (VBR) characteristics. In this paper we propose FHCF, a simple and e±cient scheduling algorithm for 802.11e that aims to be fair for both CBR and VBR °ows. FHCF uses queue length estimations to tune its time allocation to mobile stations. We present analytical model evaluations and a set of simulations results, and provide performance comparisons with the 802.11e HCF referenced scheduler. Our performance study indicates that FHCF provides good fairness while supporting bandwidth and delay requirements for a large range of network loads

ANALISIS MODEL TXOP WLAN IEEE 802.11E/G MENGGUNAKAN DISCRETE PHASE-TYPE UNTUK LAYANAN RT-CBR

Wireless Local Area Network (WLAN) merupakan solusi untuk keperluan manusia yang memerlukan komunikasi data cepat dan fleksibel. Terdapat banyak standard WLAN di dunia, salah satunya adalah IEEE 802.11e. Standard ini mendukung jaminan Quality of Service (QoS) sehingga dapat membuat layanan real time berjalan dengan baik, namun standard ini tidak dapat berdiri sendiri, diperlukan standard IEEE lain yang berfungsi sebagai physical layer yaitu IEEE 802.11g. Pada Tugas Akhir ini, analisis model Transmission Opportunity (TXOP) metastabil terfokus pada protokol HCF Coordinated Channel Access (HCCA) untuk layanan real time. HCCA merupakan protokol yang memberikan perlakuan sama untuk semua jenis traffic, karena karakteristik unik tersebut, protokol ini cocok digunakan untuk menangani layanan real time. Proses yang terjadi pada protokol HCCA selalu melibatkan superframe yang secara garis besar terdiri dari beacon, Contention Free Period (CFP) dan Contention Period (CP), selain itu CFP terbentuk dari PCF Inter Frame Space (PIFS), Short Inter-Frame Space (SIFS), dan TXOP. Bagian yang dianalisis hanya CFP, sedangkan bagian yang dimodelkan hanya TXOP yang durasinya dipengaruhi oleh bitrate. Pemodelan dilakukan menggunakan Discrete Phase-Type (DPH) dengan beberapa asumsi yaitu satu user hanya mendapatkan satu TXOP dan bitrate yang digunakan adalah bitrate mandatory dengan asumsi constant bitrate. Dengan melakukan pemodelan TXOP, diperoleh komposisi metastabil untuk satu superframe yang dapat menangani real time service dengan baik. Hal ini terbukti dari waktu tunggu yang diperlukan setiap user memenuhi syarat real time service jika komposisi ini digunakan dengan kondisi user yang terhubung ke Access Point (AP) selalu 100. Di samping itu, ditemukan juga panjang TXOP untuk komposisi user yang berbeda-beda

THE INFLUENCE OF MAC BUFFER ON THE CONTENTION-BASED ACCESS SCHEME WITH BURSTING OPTION FOR IEEE 802.11E WIRELESS NETWORKS

Wireless LANs are increasingly being used for inelastic applications. Currently, there is little support for quality of service in the IEEE 802.11 MAC protocol, and IEEE task group E has defined the 802.11e MAC extension. Enhanced distributed channel access (EDCA) is a contention-based scheme of the 802.11e standard. To allow a station to transmit more than one frame from a single contention, an optional feature known as controlled frame-bursting (CFB) is introduced in the standard. In this paper, we initially performed an average analysis to determine a suitable burst duration limit. Then, a detailed evaluation and comparison of the EDCA protocol with the CFB option is carried out through simulation to quantify its performance gain. The impact of the MAC transmit buffer size is also incorporated. Accordingly, we have proposed a suitable approach to guide the configuration of the burst duration limit. It is demonstrated that an optimized CFB configuration allows the MAC protocol to achieve 30% more capacity than the basic EDCA scheme

Throughput quantitative analysis of EDCA 802.11e in different scenarios

This document presents a quantitative analysis of the direct and relative throughput of IEEE 802.11e. The global throughput of an 802.11e WLAN is determined by EDCA (Enhanced Distributed Channel Access) parameters, among other aspects, that are usually configured with predetermined and static values. This study carefully evaluates the Quality of Service (QoS) of Wi-Fi with EDCA in several realistic scenarios with noise and a blend of wireless traffic (e.g., voice, video, and best effort, with Pareto distribution). The metrics of the benefits obtained in each case are compared, and the differentiated impact of network dynamics on each case is quantified. The results obtained show that the default settings are not optimal, and that with an appropriate selection, can be achieved improvements of the order of 25 %, according to the type of traffic. In addition, it could be shown the quantitative impact of each parameter EDCA on the overall performance. This study proposes a new experimental scenario based on the relative proportion of traffic present in the network. Stations have been simulated using the Möbius tool, which supports an extension of SPN (Stochastic Petri Networks), known as HSAN (Hierarchical Stochastic Activity Networks).Facultad de Informátic

Evaluation of 802.11a for streaming data in ad-hoc networks

Abstract — Advances in communication and processing have made ad-hoc networks of wireless devices a reality. One application is home entertainment systems where multiple Home-to-Home (H2O) devices collaborate as peers to stream audio and video clips to a household. In this study, we investigate the feasibility of IEEE 802.11a protocol in combination with both TCP and UDP to realize a H2O device. Challenges include lossy connections, unfair allocation of bandwidth between multiple simultaneous transmissions, and the exposed node limitation [22], [19], [13], [4]. Our primary contribution is an empirical study of 802.11a to quantify these factors and their significance. Our multi-dimensional experimental design consists of the following axes: distance between participating devices, number of intermediate H2O devices used to route a stream from a producing H2O device to a consuming H2O device, and simultaneous number of active streams in the same radio range. Both operating system and application level routing were considered. Obtained results demonstrate the following lessons. First, with a multi-hop UDP transmission, in the absence of congestion control, transient bottlenecks result in a high loss rate. Hence, a transport protocol with congestion control is essential for streaming of continuous media within a H2O cloud. Second, 802.11a does not drop TCP connections in the presence of many competing transmissions (802.11b drops connections [22]). Third, we observed fairness when transmitting several hundred Megabytes (MB) of data, among multiple competing 1-hop TCP and UDP flows. Fourth, while there is unfair allocation of bandwidth with an exposed node, the observed bandwidths are sufficient to stream a high-quality video clip (with a 4 Mbps display bandwidth requirement). These results indicate streaming of data is feasible with an ad-hoc network of wireless devices employing the 802.11a protocol. I

An analytical model for performance evaluation of multimedia applications over EDCA in an IEEE 802.11e WLAN

We extend the modeling heuristic of (Harsha et al. 2006. In IEEE IWQoS '06, pp 178-187) to evaluate the performance of an IEEE 802.11e infrastructure network carrying packet telephone calls, streaming video sessions and TCP controlled file downloads, using Enhanced Distributed Channel Access (EDCA). We identify the time boundaries of activities on the channel (called channel slot boundaries) and derive a Markov Renewal Process of the contending nodes on these epochs. This is achieved by the use of attempt probabilities of the contending nodes as those obtained from the saturation fixed point analysis of (Ramaiyan et al. 2005. In Proceedings ACM Sigmetrics, '05. Journal version accepted for publication in IEEE TON). Regenerative analysis on this MRP yields the desired steady state performance measures. We then use the MRP model to develop an effective bandwidth approach for obtaining a bound on the size of the buffer required at the video queue of the AP, such that the streaming video packet loss probability is kept to less than 1%. The results obtained match well with simulations using the network simulator, ns-2. We find that, with the default IEEE 802.11e EDCA parameters for access categories AC 1, AC 2 and AC 3, the voice call capacity decreases if even one streaming video session and one TCP file download are initiated by some wireless station. Subsequently, reducing the voice calls increases the video downlink stream throughput by 0.38 Mbps and file download capacity by 0.14 Mbps, for every voice call (for the 11 Mbps PHY). We find that a buffer size of 75KB is sufficient to ensure that the video packet loss probability at the QAP is within 1%

A differentiated Services Architecture for Quality of Service Provisioning in Wireless Local Area Networks

Currently the issue of Quality of Service (QoS) is a major problem in IP networks due to the growth in multimedia traffic (e.g. voice and video applications) and therefore many mechanisms like IntServ, DiffServ, etc. have been proposed. Since the IEEE 802.11b (or Wi-Fi) standard was approved in 1999, it has gained in popularity to become the leading Wireless Local Area Network (WLAN) technology with millions of such networks deployed worldwide. Wireless networks have a limited capacity (11 Mbits/s in the case of Wi-Fi networks) owing to the limited amount of frequency spectrum available. At any given time there may be a large number of users contending for access which results in the bandwidth available to each user being severely limited. Moreover, the system does not differentiate between traffic types which means that all traffic, regardless of its importance or priority, experiences the same QoS. An important network application requiring QoS guarantees is the provision of time-bounded services, such as voice over IP and video streaming, where the combination of packet delay, jitter and packet loss will impact on the perceived QoS. Consequently this has led to a large amount of research work focussing mainly on QoS enhancement schemes for the 802.11 MAC mechanism. The Task Group E of the IEEE 802.11 working group has been developing an extension to the Wi-Fi standard that proposes to make changes to the MAC mechanism to support applications with QoS requirements. The 802.11e QoS standard is currently undergoing final revisions before approval expected sometime in 2004. As 802.11e WLAN equipment is not yet available, performance reports can only be based on simulation. The objective of this thesis was to develop a computer simulator that implements the upcoming IEEE 802.11e standard and to use this simulator to evaluate the QoS performance enhancement potential of 802.11e. This thesis discusses the QoS facilities, analyses the MAC protocol enhancements and compares them with the original 802.11 standard. The issue of QoS provisioning is primarily concerned with providing predictable performance guarantees with regard to throughput, packet delay, jitter and packet loss. The simulated results indicate that the proposed QoS enhancements to the MAC will considerably improve QoS performance in 802.11b WLANs. However, in order for the proposed 802.11e QoS mechanism to be effective the 802.11e parameters will need to be continually adjusted in order to ensure QoS guarantees are fulfilled for all traffic loads

An admission control scheme for IEEE 802.11e wireless local area networks

Includes bibliographical references (leaves 80-84).Recent times has seen a tremendous increase in the deployment and use of 802.11 Wireless Local Area Networks (WLANs). These networks are easy to deploy and maintain, while providing reasonably high data rates at a low cost. In the paradigm of Next-Generation-Networks (NGNs), WLANs can be seen as an important access network technology to support IP multimedia services. However a traditional WLAN does not provide Quality of Service (QoS) support since it was originally designed for best effort operation. The IEEE 802. 11e standard was introduced to overcome the lack of QoS support for the legacy IEEE 802 .11 WLANs. It enhances the Media Access Control (MAC) layer operations to incorporate service differentiation. However, there is a need to prevent overloading of wireless channels, since the QoS experienced by traffic flows is degraded with heavily loaded channels. An admission control scheme for IEEE 802.11e WLANs would be the best solution to limit the amount of multimedia traffic so that channel overloading can be prevented. Some of the work in the literature proposes admission control solutions to protect the QoS of real-time traffic for IEEE 802.11e Enhanced Distributed Channel Access (EDCA). However, these solutions often under-utilize the resources of the wireless channels. A measurement-aided model-based admission control scheme for IEEE 802.11e EDCA WLANs is proposed to provide reasonable bandwidth guarantees to all existing flows. The admission control scheme makes use of bandwidth estimations that allows the bandwidth guarantees of all the flows that are admitted into the network to be protected. The bandwidth estimations are obtained using a developed analytical model of IEEE 802.11e EDCA channels. The admission control scheme also aims to accept the maximum amount of flows that can be accommodated by the network's resources. Through simulations, the performance of the proposed admission control scheme is evaluated using NS-2. Results show that accurate bandwidth estimations can be obtained when comparing the estimated achievable bandwidth to actual simulated bandwidth. The results also validate that the bandwidth needs of all admitted traffic are always satisfied when the admission control scheme is applied. It was also found that the admission control scheme allows the maximum amount of flows to be admitted into the network, according the network's capacity