Wireless Voip Service Quality Of The Research

With the development of network and wireless technologies, researches about WLAN become popular topics in the field of communications. Many scientists and researchers are researching, analyzing, and modifying existing standards and protocols through methods of modeling, simulating and experiments. All these efforts make it possible and practical to develop WLAN constantly.At the beginning, the background and the value of the thesis are introduced, and then the basic concepts, knowledge, related standards and protocols of WLAN. Followed, we proposed two new strategies about WLAN MAC (Media Access Control) protocol. The first is RTS/CTS adaptive access mechanism. There are already many researches about RTS/CTS, which focus on all kinds of aspects, such as "Hidden Stations", power consumption, influence of RTS/CTS threshold, and there are also many different methods to analyze existing standards and protocols, and many new strategies, schemes and algorithms proposed already. In this thesis, the evaluation of active station numbers and network throughput are concerned. Through the evaluation result, stations will dynamically decide whether to use RTS/CTS handshake before data frame to reduce network bandwidth waste due to collisions without RTS/CTS and overload caused by RTS/CTS.The second proposed strategy is VoIP traffic tolerance mechanism. Once a packet is detected error, with typical MAC protocol of WLAN, it will be discarded, which is necessary to data traffic. But it is unnecessary to voice traffic, because a few bit errors in voice packet would only bring some noises, which will not affect communication seriously. What is more, the MAC checking mechanism will cause more delay, jitter and network resource wastes. Thus, we proposed VoIP traffic tolerance mechanism, which allow voice frame with error pass CRC check to reduce unnecessary retransmissions, finally improve QoS of VoIP traffic.In order to do the VoIP QoS Research in the real networks, we constructed a wired-wireless VoIP test-bed based on the Operation System of Linux. Test-bed is an open platform. With a few modifications and supplements, many other algorithms and strategies can be implemented. Test-bed is implemented in the environment of IPv4 firstly, then upgrade to IPv6. Besides constructing test-bed, we used the simulator tools, e.g. NS-2, to simulate and analyze the proposed strategies.At last, related research works in the thesis are briefly concluded, and the next plans and prospects of the research are described.