Abstract

The Enhanced Coordination Channel Access (EDCA) mechanism is a 802.11e WG’s initiative to provide Quality of Service (QoS) guarantees in 802.11-based wireless networks. Although EDCA introduces new mechanisms for differentiated medium access, it falls short in ensuring (i) intra-class QoS guarantees since flows belonging to the same service class (AC) are assigned the same MAC parameters regardless of their respective bit rate, which leads to throughput fairness rather than perceived QoS fairness, and (ii) sustained QoS guarantees by developing some sort of admission control mechanism to protect QoS of flows being served. In this paper, we propose a new MAC protocol featuring a dynamic channel reservation by using dynamic TXOPlimit parameter assignment along with a fully distributed admission control algorithm. By monitoring the dynamics MAC’s AC queues, each AC figures out during runtime the TXOPlimit’s value that best accommodates the application’s data rate. TXOPlimit values are determined based on instantaneous network availability modelling taking into account key factors (e.g., contention level, network load, etc.) that influence flows’ QoS performances. We generalize this model so that each AC active in the network may a priori assess the achievable QoS. This later model is used to design a fully-distributed admission control algorithm that regulates the network load to protect the already admitted flows from new entering flows. Simulation results show that compared to both EDCA and AEDCF (Adaptive EDCF), our protocol excels, in terms of network utilization and ability to guarantee the same QoS metrics’ performances to flows of the same AC (intra-class). The admission control mechanism ensures high protection to the admitted flows while maintaining high network utilisation.

Keywords: IEEE 802.11e; QoS; Admission control; Intra-class QoS guaranteed

Article Outline

1. Introduction

2. Background and related work

2.1. Basic access mechanism

2.2. Quality of service

2.2.1. Before IEEE 802.11e

2.2.2. IEEE 802.11e draft: EDCA

2.2.3. After IEEE 802.11e

3. Enhanced TXOP

3.1. Context

3.2. ETXOP: TXOPlimit calculation

3.3. ETXOP: Intra-AC QoS differentiation

4. Admission control

4.1. Related works

4.2. ETXOP: Admission control mechanism

5. Simulation and results

5.1. ETXOP versus EDCA and AEDCF

5.2. ETXOP with admission control

6. Conclusion

References

Vitae