Analysis And Research Of The VoIP QoS Over WLAN

VoIP over WLAN which is called the VoWLAN is an application of VoIP based on the WLAN.VoIP and WLAN are popular network technologies which are developping fast nowdays.VoIP has the advantages of low-cost and high voice quality,the WLAN has the advantages of mobility,low-cost and the property that can be used in special environment etc.Combined with these two technologies,the VoWLAN has all of the advantages and has a very wide development prospect.The VoWLAN which applied in the environment of wireless can satisfy the requirement of users and market except it has the same quality of service as the wired VoIP,but the original design of the WLAN didn't consider the real-time requirement of the voice traffic,it cann't support favorable quality of service for the voice business which is sensitive to the time delay,so that the problem how to improve the quality of service of the VoIP system has become a very important problem in the study of VoWLAN.This paper has studied and analyzed the QoS mechanism of the VoIP based on the WLAN , an improved quality of service mechanism and improved ideas have been proposed.In order to improve the QoS supportion of the WLAN for the voice and the other real-time multimedia business,this paper has mainly studied some improved PCF algorithm nowdays,summarized some PCF improved ideas for the QoS of VoIP business and proposed new improved PCF polling mechanism.The new PCF polling mechanism has been divided into two classes,the first calss uses multi-polling mechanism,gives the VoIP business high priority and the VoIP frame can be sended constantly,the main improvement of the algorithm is:1. The algorithm uses super poll mechanism which instead of the PCF single polling schema.The super poll is multi-polling schema,which can efficiently reduce the overhead of the polling frame.2.The priority schema has been introduced into the new algorithm.In the improved PCF polling mechanism,the priority of the VoIP frame has been increased,the VoIP stream can get constantly services,the QoS of the VoIP can be improved.3.The priority and the state of the stations has been differentiated in the new PCF mechanism.The stations that sended the VoIP frame being in the state of real-time,they have the highest priority,and can be firstly polled at every round of the poll.4.The stations uses queues to manage the MAC frames. Every stations have two buffer queues,separately loaded the VoIP frames and the other frames.The priority of the VoIP queue is higher than the other queue.In order to ensure the other stations has the right of sending frames, and solve the problem of overflow lies in the AP cache, this paper proposes the second class of PCF polling mechanism,which also based on the multi-polling scheme,the second PCF polling mechanism can slove the problem that one station uses the channel too long.