Simulation Researches On VOIP QoS In IEEE 802.11 Wireless Local Areea Lan Netwrok

With the rapid developments in Internet and wireless technologies, the wireless local area network (WLAN) has attained the widespread application. The increased demands for more real-time services makes the QOS(quality of service) become a key problem in WLAN.WLAN performs the access control, medium sharing visit and channel resource distribution through the (media access control) (MAC) layer, due to which, researches on MAC protocol becomes a hot spot area.As the present mainstream WLAN standard, IEEE802.11 defines two access protocols in the MAC level, i.e., the distributed coordination function (DCF) and point coordination function (PCF). DCF has the advantage being simple and easy to be implemented, which leads it wider applications than PCF. However, the original DCF protocol defined in IEEE802.11 cannot support real-time services with satisfactory QoS.In recent years, there have been many remarkable research results of DCF mechanisms for QOS improvement.Possessing advantages including low cost and various services, voice over IP (VOIP) technology can transport voice packets through internet and have been used extensively. Many researchers start to investigate transmitting VOIP packets in WLAN. This thesis analyzes the DCF working principles and system performance firstly. Further, referring to the existing research results, the thesis propose a new idea to achieve higher utilize efficiency and lower delay. The proposed algorithm divides the date frames into voice stream and common date stream. When voice stream exists, higher transmission priority should be allocated to the voice data. While when it is detected that the voice transmission is suspended, the priority of common data services is adjusted adaptively so as to make full use of wireless resources and therefore increase the system throughput.A system simulation platform is built by means of the software NS2, in which both VOIP frames and data frames are involved. During the simulation, VOIP communication lasts some time before it stops. The system throughput simulation results plotted show that the new algorithm can improve the throughput performance to some extent and satisfy the low-delay demand of voice communication.