Document Type

Theses, Masters


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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.