IEEE 802.11Wireless LAN
Being one of the most extended wireless technologies in wireless communication networks, IEEE 802.11 wireless LAN offers simplicity, flexibility and cost effectiveness as its main characteristics. This wireless technology provides communication between peoples everywhere and computing environment at any place where peoples needed wireless communication to communicate. At the same time, number of users for multimedia applications increased. Nowadays, peoples want more of the high-speed video, audio, voice and web services anywhere and anytime. Unfortunately, these multimedia applications require Quality of Service support such as guaranteed bandwidth, delay, jitter, ...view middle of the document...
There are few ways to characterize Quality of Service in Wireless Local Area Network. For example, parameterized or prioritized Quality of Service. Basically, Quality of Service is the ability of network element, for example, an application, a host or router, to provide some levels of assurance for consistent network data delivery.
Parameterized Quality of Service is a strict requirement of Quality of Service that shows in terms of quantitative values, such as data rate, delay bound, and jitter bound. This quantitative value is expected to be met within the medium access control data service in the transferring of data frames in a Traffic Specification.
Prioritized Quality of Service is expressed in the terms of relative delivery priority, which is used to be within the medium access control data service in the transfer of data frames between peer stations. The values of Quality of Service parameters such as data rate, delay bound, and jitter bound, may be differ in the transfer of data frames, without the need to reserve the required resources by negotiating the Traffic Specification.
Quality of Service limitations of Distributed Coordination Function
Distributed Coordination Function is a distributed medium access scheme based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. A station must sense the medium before initiating a packet transmission. This scheme only supports best-effort services but not any Quality of Service guarantees. Basically, time-based application services such as Voice over Internet Protocol, or Audio/Video Conferencing require specified bandwidth, delay and jitter but can tolerate some losses.
However, in Distributed Coordination Function mode, all the stations in same BSS compete for the resources and channel with some priorities. There is no differentiation mechanism to guarantee bandwidth, packet delay and jitter for high priority station or multimedia flows.
Figure 1: Simulation topology of Distributed Coordination Function in ad-hoc mode.
In the simulation topology, there is no mobility between the devices. Each station operates at IEEE 802.11a and transmits three types of traffic which is audio, video, and background traffic to each other. The packet size for audio and video is 160 bytes and 1280 bytes respectively while the sending rate for the background traffic is 128 KB/s, using a 1600 bytes packet size. Throughput for each of the traffic is about 7.8 KB/s for audio, video for 78 KB/s and about 125 KB/s for background traffic. the average throughput for three kinds of flows per stations are almost stable when the channel load rate is less than 70% when the number of stations is up to 10.
When the number of station is larger than 10, the throughput of the three traffics decreases. For example, the throughput is around 60% when the number of stations is 18. The mean delays of the three flows increase up to 420ms and almost the same for all the three flows....