QoS Mechanisms for the MAC Protocol of IEEE 802.11 WLANs

Abstract

There are two essential ingredients in order for any telecommunications system to be able to provide Qualityof-Service (QoS) guarantees: connection admission control (CAC) and service differentiation. In wireless local area networks (WLANs), it is essential to carry out these functions at the MAC level. The original version of IEEE 802.11 medium access control (MAC) protocol for WLANs does not include either function. The IEEE 802.11e draft standard includes new features to facilitate and promote the provision of QoS guarantees, but no specific mechanisms are defined in the protocol to avoid over saturating the medium (via CAC) or to decide how to assign the available resources (via service differentiation through scheduling). This paper introduces specific mechanisms for both admission control and service differentiation into the IEEE 802.11 MAC protocol. The main contributions of this work are a novel CAC algorithm for leaky-bucket constrained traffic streams, an original frame scheduling mechanism referred to as DM-SCFQ, and a simulation study of the performance of a WLAN including these features.

Cross-layer medium access control protocol with quality-of-service guarantees for wireless sensor networks

“…We argue that guaranteeing a certain amount of bandwidth is enough for QoS assurance, i.e., throughput, delay, jitter, and losses due to buffer overflow will be bounded as a consequence, as explained in [28]. This will be discussed in more detail later.…”

“…All nodes start with an available bandwidth equal to the wireless channel's achievable effective data rate R, which depends on the underlying physical layer and medium access policy. For instance, in a polling-based system such as the one assumed in this work, the achievable throughput is about 85% of the channel gross bit rate [28]. In addition, R can be reduced further to account for the expected channel errors, which are present in any transmission medium but are especially common in wireless environments.…”

“…If the maximum amount of data that can be generated by a node during a cycle can be known beforehand, such as in constant-bit-rate or leaky-bucketconstrained streams [28], then deterministic (hard) QoS guarantees can be offered. If, on the other hand, traffic presents a higher variability so that reserving enough resources to process the maximum amount of data that can be generated during a cycle is not practical, then stochastic (soft) guarantees can still be offered, in the sense that QoS requirements can be violated but with a quantifiable low probability.…”

Multi-Constrained Routing Algorithm for Multimedia Communications in Wireless Sensor Networks

“…Several main MAC layer protocols have been developed for multimedia communications in sensor networks. IEEE 802.11e scheme has provisions for service differentiation at MAC layer in sensor networks, though it was proposed for ad hoc networks initially [1]. In this scheme, the service differentiation is obtained by changing the duration of the Inter-Frame Spacing (IFS) and the Contention Window (CW) size based on the priority of the packet.…”

Implementing QoS Support in a Wireless Home Network

“…Most of the studies propose different kinds of medium access control (MAC) layer enhancements to WLAN technologies for QoS support (e.g. [2]). Our approach is different since we want to be able to utilize devices conforming to the current standards for MAC layer operation and based on them, build up a system that is able to support the needs of new home applications.…”