Performance Of Streaming Media In IEEE 802.11b WLAN

Streaming media and Wireless networks are two of the most popular and fast-growing Internet technologies.They have been bringing revolutionary changes to the promulgation and communication of information, and making fundamental impact on people's life. With the 3G's coming age, application of wireless streaming will find huge potential market foregrounds. The research of wireless streaming technology has drawn tremendous attention from both academia and industry. Howerver, not only are bandwidth and buffer of the wireless systems usually more constrained than their wireline counterparts, but also the wireless channel has higher inherent loss and delay. Therefore, streaming application faces several challenges when it comes to wireless environment. In this paper, with a novel emulator being introduced, we will provide some insight to the performance of streaming media in IEEE 802.11b WLAN. Using NIST Net, a popular network emulation tool to finely controll the network conditions such as capacity, loss rate and latency, we firstly examined the behavior of Windows Streaming Media (WSM)and Real Streaming Media(RSM)under a wide range of network conditions. The experimental results show that WSM and RSM have diffenrent sensibility to different network factors and there is great unfairness in capacity allocation. Such a characterization is useful in capacity planning studies for the design, deployment, and evolution of larger WLANs. Then, the author analysized the effect of node mobility on streaming media performance and seek to understand the relationship between wireless channel characteristics (i.e., channel error rate, packet loss, retransmission, delay) and the user-perceived quality of a video stream. Our experimental results illustrate two main points: First, wireless media streaming performance can degrade significantly in the presence of user mobility. Second, the performance degradation affects all other clients in WLAN, not just the clients who are mobile. One possible solution is to use per-flow queueing at the AP and to utilize a buffer management scheme that provides fairness between flows. Lastly, we studied the performance of WSM streaming over IEEE 802.11b WLAN under different channel conditions. The 802.11b MAC-layer retransmission mechanism is able to hide most physical-layer channel errors from higher-layer protocols. When needed, some errors are still left to the application layer to solve, which can trigger application-layer retransmission. One of solutions is to use dynamic packet fragmentation in order to reduce the impacts of wireless channel errors on media streaming performance.