Vowlan Technology, The Mac Research And Improvement

Wireless network, as an access technology, is playing a more and more important role in many occasions, the requirements to transmit real-time traffic such as voice, video is increasing in VoWLAN, and so IEEE developed 802.11e based on 802.11. The protocol can improve mechanism of WLAN access to supports quality of service of voice (QoS) and video real-time traffic. Real-time services such as audio and videoconferences mean requirment some specified bandwidth, delay and jitter guarantee.This thesis pay attention to 802.11e mainly, According to access mechine of EDCA (Enhance DCF) in the protocol of 802.11e, author is putting forward improved DEDCA (Dynamic Enhance DCF) mechanism, the mechanism let net-nodes dynamic access based on performance of network in WLAN. There is not EDCA moduling in simulative softwar OPNET Modeler, author buildes modeling of EDCA using program c and proves validity of DEDCA theoretically by simulation experments.At first, the standard of wireless LAN, the QoS of WLAN, and DCF are introduced, and DCF is simulated by OPNET, the parameter of throughput and delay are analyzed, which effect the network performance, anthor point out the shortcoming when it apply to real-time traffic, 802. 11e is imported,which set tup the priority ranks of traffics and can guarantee the QoS of Voice and Vedio. In the thesis, 802.11e and EDCA access mechanism is investigated, Analyses on throughput of any net-node theoretically, has attained the connection betwixt throughout and back-off windows, then, EDCA is simulated by OPNET, and the performance of EDCA and DCF are compared. EDCA can guarantee QoS of real-time traffics by impropriation the channel of Data.Then, VoWLAN is presented simply, has brought forward DEDCA access mechanism, which adapt to VoWLAN technology, this mechanism has imported channel estate CS, dynamic back-off window and a new back-off way . The formula of back-off valve value and relation betwixt channel estate and the value ofback-off windows are found, then, proving the validity of DEDCA which adapt to VoWLAN technology by simulation.