【作者】 李静远；

【导师】 黄刘生；

【作者基本信息】 中国科学技术大学 ， 计算机软件与理论， 2009， 博士

【摘要】 自二十世纪九十年代互联网向公众开放以来,计算机网络发展日新月异,各种新的系统层出不穷。因特网(Internet)的结构随着上层应用程序对网络需求的变化,经历了从对等网络模式(Peer-to-Peer or P2P)向客户端/服务器模式(Client/Server),再返回到P2P模式的发展历程。随着计算机终端设备和网络设备的快速发展,伴随网络处理和传输数据能力的提升,P2P系统的应用范围愈发广泛,这其中就包括了文件共享系统,视频点播系统,以及实时语音和视频电话系统等。然而,最近几年P2P应用程序的发展远远超过了网络传输能力和网络协议的发展速度,造成网络的严重拥塞。由于IPv4没有提供数据的分级传输机制,而能提供分级传输机制的IPv6协议又迟迟无法推广,造成P2P数据流占用了绝大多数网络带宽,严重影响到其它网络应用程序的性能。网络服务提供商花费重金扩展网络容量也无法满足庞大的用户需求,因此只好使用多种手段限制、甚至阻断P2P应用程序的数据传输。同时,随着各种无线网络技术的发展,越来越多的P2P系统开始尝试部署于无线网络上。而无线网络所能提供的数据传输速率和稳定性又远远不及有线网络,这更加重了大规模P2P系统的部署难度。本文提出一系列平衡网络流量,缓解矛盾的方法,以应对P2P应用系统与网络发展不平衡所带来的矛盾。在当前P2P系统的无线化大背景下,本文着重研究WiMAX、Wi-Fi、3G等无线网络的特点,在AnyServer平台的支持下,提出了在这些网络上高效部署P2P文件共享系统和视频电话系统的方法。本文的主要内容与创新点如下:首先,本文提出了一种在包含有线结点和无线结点的混合P2P文件共享系统下,保护无线结点能量,以延长其服务时间的方法。通过实验我们发现,在拥有较大数量无线结点的P2P文件共享系统中,如果不考虑无线结点的能量和通信能力,会导致无线结点过早能量耗尽,令系统中结点数量显著减少,从而反过来严重影响系统的覆盖率和文件共享功能的效率。实验证明,在80%的结点是无线结点的系统中,我们的资源结点选择算法可以使无线结点的失效率降低50%以上,并令资源文件传输总时间降低超过50%,从而有效改善混合P2P网络中无线结点的生存环境。第二,本文提出了一个基于WiMAX和Wi-Fi网络的P2P文件共享系统的应用层网络拓扑结构优化模型。考虑到无线城域网WiMAX即将产品化,如果能充分利用成熟的无线局域网技术Wi-Fi的特性,城际无线网络上数据共享系统拥有广阔的应用前景。在这样的混合无线网络中,如果不考虑无线网络空中接口资源紧张的特点,随意搭建应用层拓扑结构,会导致大量宝贵带宽被浪费。因此本文提出层次化P2P共享系统,根据WiMAX Mesh网络的特点,在WiMAX基站骨干网络层和客户站所组成的Mesh网络层中建立层次化分布式查找结构。模拟实验证明,对于拥有率超过2.5%的资源,本文提出的查找算法在本地Mesh网络发现该资源的概率超过90%,从而有效节省了网络空中接口资源,提高了资源查找效率。第三,本文提出了一个基于会话初始化协议(Session Initiation Protocol orSIP)的自适应视频IP电话(Voice and Video over IP or VVoIP)系统。由于IPv4网络中地址不足,且网络安全问题比较突出,目前网络中大量部署了防火墙和网络地址转换器(Network Address Translator or NAT)。由于SIP/SDP协议族对NAT穿越方面没有作具体规定,使得两个VVoIP客户端实现点到点传输会遇到问题。ICE(Interactive Connectivity Establishment)协议的出现填补了NAT穿透的空白,但就VVoIP应用来说,ICE显得比较复杂,所消耗的资源也较大。而本文提出的基于AnyServer平台的自适应SIP VVoIP系统能够保证VVoIP客户端之间的P2P实时通信。实验证明,本系统能够减轻流媒体服务器的压力,降低实时会话的网络时延。第四,本文提出了一组基于SIP的VVoIP系统中音频/视频数据的协作传输算法。音频电话VoIP向视频电话VVolP的转变,大大缩短了人与人之间的空间距离。然而,VVoIp中视频流数据的规模远大于音频流数据,无序的视频/音频流传输会使得VVoIP客户端的话音效果受到较大影响,尤其是在无线网络接入设备上运行的VVoIP客户端上,话音质量的下降现象尤为明显。本文提出了一组协作传输算法(Voice and Video Transmission Strategies of VVTS),能够有效减小数据传输速率的波动,在尽量不降低视频质量的前提下,提高话音质量。最后,本文介绍了支持本文实验的AnyServer平台的总体架构,以及各个子系统的框架和实现细节,并对VVoIP系统今后的发展方向进行了讨论。更多还原

【Abstract】 Since the opening of the networks to public interests in the 1990s,the Internet is booming,with thousands of applications and services throughout the globe.According to the evolution of the application requirements,the structure of the Internet changed from peer-to-peer(P2P) mode to client/server mode,and then back to P2P mode.Through the rapid development of end host equipments and network facilities, the data processing and transmission capability of the Internet is also growing,making the prosperous P2P applications even more prosperous.New applications include file sharing systems,video on demand systems and video over IP systems.However,the development of P2P applications overwhelms the increment of the Internet transmission abilities in recent years,causing serious network congestions. IPv4 does not provide Quality of Service(QoS) assured transmission mechanism;while IPv6 does provide the QoS mechanism,the massive deployment of IPv6 has been postponed for years.Without the QoS mechanism,P2P traffic occupies most of the bandwidth, severely downgrades the performance of other network services.Internet service providers(ISP) spent vast sums of money on enhancing the network facilities,but failed to fulfil the enormous requirement.Therefore,ISPs have no choice but to limit,or even block the traffic caused by P2P applications.The spread of P2P systems to wireless networks deteriorates the situation,because the wireless networks have less data processing capabilities than wireline networks.In this dissertation,we propose methods to balance the network traffic,in order to relieve the tensions caused by P2P applications. We also make effort to build P2P file sharing applications and a VVoIP application on AnyServer,a cross network platform for seamless data interoperability.The main contributions of this dissertation are:Firstly,we propose a scoring mechanism to protect wireless peers in hybrid P2P file sharing structure.In a P2P file sharing system with vast wireless peers,if we do not seriously consider the capability of wireless peers,they may be out of service soon, which in turn severely downgrades the efficiency of the system.In a hybrid P2P system where 80%of the peers are wireless peers,The source peer selection algorithm we put forth can reduce the out-of-service rate of wireless peers by 50%,and save the total file transmission time by 50%,effectively improving the overall performance of the hybrid P2P system.Secondly,we provide an optimized model of P2P file sharing system based on WiMAX and Wi-Fi.WiMAX and Wi-Fi are highly complementary.Hence,it is very profitable to build up P2P systems over WiMAX and Wi-Fi networks simultaneously.In this dissertation,we propose a layered distributed P2P structure for the application layer overlay network,in order to save the air interface of the wireless networks,and shorten the lookup time.By simulations,we claimed that the requested file can be found in the local subscribe station mesh network in 90%of the time,if that file’s popularity rate is over 2.5%.Thirdly,we propose an adaptive SIP-based VVolP system.Because of the shortness of IP addresses in IPv4,NAT are massively deployed in the network.SIP/SDP protocol stack does not define the behavior of SIP client with NAT.ICE is a good solution for NAT,but quite complicating for VVoIP applications.The SIP-based adaptive VVoIP system we implemented can guarantee P2P connection between two clients. Through a series of experiments,we proved that the system can relieve the pressure of multimedia server,and reduce the delay time of the session.Fourthly,We present a series of cooperative transmission strategies for SIP-based VVoIP system over AnyServer.The emergence of VVoIP really reduces the size of the world.However,in a VVoIP system,the data size of the video stream overwhelms the data size of the voice data.If video data are transmitted without consideration of the voice data,serious jitters may occur.In this dissertation,we provide a series of transmission strategies called VVTS,which can effectively reduce the fluctuation of data transmission,and improve the voice quality of the system.Finally,we describe the whole structure of AnyServer in detail,and discuss the development trends of P2P VVoIP systems in the near future.更多还原