无线VoIP业务服务质量的研究

【作者】 宋嵩；

【导师】 李康；

【作者基本信息】 山东大学 ， 通信与信息系统， 2005， 硕士

【摘要】 随着网络通信和无线通信的不断发展,无线局域网已成为通信领域学界研究的热点。很多专家学者在针对现有的无线局域网标准、协议通过建模、仿真和实验等方式进行研究、分析以及改进。通过不懈的努力,无线局域网的标准、协议得到了不断的完善和发展。 论文首先介绍了课题的背景、选题意义,然后介绍了无线局域网的一些基本概念、基本知识以及一些相关标准、协议等。在此基础上,提出了两种MAC协议改进策略。第一种改进策略是RTS/CTS自适应接入机制。关于RTS/CTS的研究也已经有很多,但各有侧重,有的侧重于解决隐藏站点问题,有的侧重于能量最省,有的侧重于RTS/CTS阈值影响。针对不同的方面,不同的学者以各种不同的方式进行了不同的研究,分析了现有标准、协议的网络性能以及各种参数对网络性能的影响等,提出了各种改进策略、方案和算法。本论文通过对网络中的站点数、对网络的吞吐量进行分布式估计,自适应地选择RTS/CTS机制,尽最大可能地减小由于网络碰撞而产生的带宽资源损失和由于使用RTS/CTS所产生的额外网络开销造成的带宽资源损失。 第二种改进策略是VoIP业务容错机制。在WLAN的MAC协议中,一旦数据帧出现校验错误,就将被丢弃,这对于准确性要求比较高的数据传输是需要和必要的,但对于语音传输来讲,往往没有必要。因为对于语音传输来讲,一些突发错误只会引起一点噪音,而并不会产生太大影响,所以这时严格的帧校验只会造成不必要的数据重传和由此而引起的延时、延时抖动和网络资源浪费。为此,论文提出了VoIP业务容错机制,对VoIP业务在MAC层进行容错处理,忽略CRC校验,减少不必要的重传,提高VoIP业务的总体服务质量。 为了便于在实际网络进行无线VoIP服务质量的研究,我们使用Linux操作系统在无线局域网中搭建了实验测试平台。测试平台具有很好的开放性,在此基础上稍加修改、扩充就可以实现其它各种算法、策略。测试平台首先在IPv4下实现,然后升级到IPv6网络环境中。除了搭建测试平台之外,还使用网络仿真更多还原

【Abstract】 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.更多还原