Adaptive EDCF: Enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks

This paper describes an adaptive service differentiation scheme for QoS enhancement in IEEE 802.11 wireless ad-hoc networks. Our approach, called adaptive enhanced distributed coordination function (AEDCF), is derived from the new EDCF introduced in the upcoming IEEE 802.11e standard. Our scheme aims to share the transmission channel efficiently. Relative priorities are provisioned by adjusting the size of the contention window (CW) of each traffic class taking into account both applications requirements and network conditions. We evaluate through simulations the performance of AEDCF and compare it with the EDCF scheme proposed in the 802.11e. Results show that AEDCF outperforms the basic EDCF, especially at high traffic load conditions. Indeed, our scheme increases the medium utilization ratio and reduces for more than 50% the collision rate. While achieving delay differentiation, the overall goodput obtained is up to 25% higher than EDCF. Moreover, the complexity of AEDCF remains similar to the EDCF scheme, enabling the design of cheap implementations

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

A study of QoS support for real time multimedia communication over IEEE802.11 WLAN : a thesis presented in partial fulfillment of the requirements for the degree of Master of Engineering in Computer Systems Engineering, Massey University, Albany, New Zealand

Quality of Service (QoS) is becoming a key problem for Real Time (RT) traffic transmitted over Wireless Local Area Network (WLAN). In this project the recent proposals for enhanced QoS performance for RT multimedia is evaluated and analyzed. Two simulation models for EDCF and HCF protocols are explored using OPNET and NS-2 simulation packages respectively. From the results of the simulation, we have studied the limitations of the 802.1 le standard for RT multimedia communication and analysed the reasons of the limitations happened and proposed the solutions for improvement. Since RT multimedia communication encompasses time-sensitive traffic, the measure of quality of service generally is minimal delay (latency) and delay variation (jitter). 802.11 WLAN standard focuses on the PHY layer and the MAC layer. The transmitted data rate on PHY layer are increased on standards 802.1 lb, a, g, j, n by different code mapping technologies while 802.1 le is developed specially for the QoS performance of RT-traffics at the MAC layer. Enhancing the MAC layer protocols are the significant topic for guaranteeing the QoS performance of RT-traffics. The original MAC protocols of 802.11 are DCF (Distributed Coordination Function) and PCF (Point Coordinator Function). They cannot achieve the required QoS performance for the RT-traffic transmission. IEEE802.lle draft has developed EDCF and HCF instead. Simulation results of EDCF and HCF models that we explored by OPNET and NS-2, show that minimal latency and jitter can be achieved. However, the limitations of EDCF and HCF are identified from the simulation results. EDCF is not stable under the high network loading. The channel utilization is low by both protocols. Furthermore, the fairness index is very poor by the HCF. It means the low priority traffic should starve in the WLAN network. All these limitations are due to the priority mechanism of the protocols. We propose a future work to develop dynamic self-adaptive 802.11c protocol as practical research directions. Because of the uncertainly in the EDCF in the heavy loading, we can add some parameters to the traffic loading and channel condition efficiently. We provide indications for adding some parameters to increase the EDCF performance and channel utilization. Because all the limitations are due to the priority mechanism, the other direction is doing away with the priority rule for reasonable bandwidth allocation. We have established that the channel utilization can be increased and collision time can be reduced for RT-traffics over the EDCF protocol. These parameters can include loading rate, collision rate and total throughput saturation. Further simulation should look for optimum values for the parameters. Because of the huge polling-induced overheads, HCF has the unsatisfied tradeoff. This leads to poor fairness and poor throughput. By developing enhanced HCF it may be possible to enhance the RI polling interval and TXOP allocation mechanism to get better fairness index and channel utilization. From the simulation, we noticed that the traffics deployment could affect the total QoS performance, an indication to explore whether the classification of traffics deployments to different categories is a good idea. With different load-based traffic categories, QoS may be enhanced by appropriate bandwidth allocation Strategy

Supporting Service Differentiation with Enhancements of the IEEE 802.11 MAC Protocol: Models and Analysis

As one of the fastest growing wireless access technologies, Wireless LANs must evolve to support adequate degrees of service differentiation. Unfortunately, current WLAN standards like IEEE 802.11 Distributed Coordination Function (DCF) lack this ability. Work is in progress to define an enhanced version capable of supporting QoS for multimedia traffic at the MAC layer. In this paper, we aim at gaining insight into three mechanisms to differentiate among traffic categories, i.e., differentiating the minimum contention window size, the Inter-Frame Spacing (IFS) and the length of the packet payload according to the priority of different traffic categories. We propose an analysis model to compute the throughput and packet transmission delays. In additions, we derive approximations to get simpler but more meaningful relationships among different parameters. Comparisons with discrete-event simulation results show that a very good accuracy of performance evaluation can be achieved by using the proposed analysis model

A simple and fair proposal to improve the performance of the IEEE 802.11e enhanced coordination function

A simple and fair proposal to improve the performance of the IEEE 802.11e standard is presented in this paper. Our proposal is accomplished by means of increasing the priority of those queues that have not been able to transmit during certain period of time, depending on the elapsed time waiting to transmit. Results show that this proposal improves the performance of wireless networks using IEEE 802.11e EDCF since low priority queues reduce their waiting time to access the channel and high priority queues are not degraded.8th IFIP/IEEE International conference on Mobile and Wireless CommunicationRed de Universidades con Carreras en Informática (RedUNCI

WLAN 802.11e evaluation performance using OPNET

The low cost and easy deployment of Wireless LAN 802.11 standard means it becomes more and more popular, but it has a vital drawback with regard to Quality of Service (QoS). QoS defines the ability of network to introduce consistent services for data transmission, and is evaluated in terms of specific parameters such as jitter, delay, and packet loss. These parameters describe data traffic quality over a network. Service differentiation should be offered to let higher priority multimedia traffic to get a preferred treatment. This deficiency of Wireless LAN 802.11 MAC mechanisms in offering QoS support is a major obstacle in the adaptation of modern multimedia applications in Wireless LAN 802.11 networks. This paper aims to build different scenarios to evaluate QoS characteristics and to examine the effect of enhancement on the QoS. The evaluation, implemented using the OPNET simulator, will contain the different parameters of Wireless LAN 802.11e to see how this enhancement in distributed channel access increases the performance over the Wireless LAN 802.11 standard. The results give a clear picture that the enhanced standard offers a very effective service mechanism to provide QoS support

Analysis of Packet Throughput and Delay in IEEE 802.11 WLANs with TCP Traffic

The IEEE 802.11 standard is a successfulwireless local area networks (WLAN) technology,because of its easy deployment. With WLAN, theability of the IEEE802.11 standard to supportmultimedia applications with high quality of service(QoS) requirements has increased. This paperevaluates the capability of QoS support in EnhancedDistributed Channel Access (EDCA) mechanism of theIEEE 802.11e standard using TCP protocol. TheEDCA is an enhancement for QoS support in 802.11.EDCA mechanisms allow prioritized medium accessfor applications with high QoS requirements byassigning different priorities to the access categories.The current work discusses the performanceevaluation of 802.11 and 802.11e by simulations usingTCP protocol. A comparative discussion between DCFund EDCA with TCP protocol is reported for differentservices, such as voice, video, best-effort andbackground traffic. Results and simulations show thatthe TCP protocol is usable for transferring audio andvideo data within special programs and applications.Moreover, it is shown that the UDP protocol with itshigher performance is more suitable for this task