P2P技术现状及未来发展

gofay

<p style="LINE-HEIGHT: 150%;"><font face="宋体"><span lang="EN-US" style="FONT-SIZE: 10.5pt; LINE-HEIGHT: 150%;">&nbsp;<b style="mso-bidi-font-weight: normal;">
                                </b></span><b style="mso-bidi-font-weight: normal;"><span style="FONT-SIZE: 10.5pt; LINE-HEIGHT: 150%;">摘要：<span lang="EN-US">2P</span>应用软件主要包括文件分发软件、语音服务软件、流媒体软件。目前<span lang="EN-US">2P</span>应用种类多、形式多样，没有统一的网络协议标准，其体系结构和组织形式也在不断发展。<span lang="EN-US">2P</span>应用已占<span lang="EN-US"><a href="http://www.cww.net.cn/opera/" target="_blank"><span lang="EN-US" style="COLOR: windowtext; TEXT-DECORATION: none; text-underline: none;"><span lang="EN-US">运营商</span></span></a></span>业务总量的<span lang="EN-US">60%</span>～<span lang="EN-US">80%</span>，<span lang="EN-US">2P</span>应用所产生的流量具有分布非均衡、上下行流量对称、流量隐蔽、数据集中等特性。在<span lang="EN-US">2P<a href="http://www.cww.net.cn/tech" target="_blank"><span lang="EN-US" style="COLOR: windowtext; TEXT-DECORATION: none; text-underline: none;"><span lang="EN-US">技术</span></span></a></span>的发展道路上，有许多尚待解决的问题。版权问题一直是<span lang="EN-US">P2P</span>发展的一个不确定因素，如何在技术层面支持合法文件的分发是需要解决的重要问题。安全问题也是<span lang="EN-US">P2P</span>领域的重要研究课题，如何在<span lang="EN-US">P2P</span>网络中实现数据存取安全、路由安全、用户身份认证和身份管理都需要进一步研究。此外，如果能够实现<span lang="EN-US">P2P</span>应用之间的统一资源定位，统一路由，使得<span lang="EN-US">P2P</span>技术有一个统一开发标准，那么就能够融合<span lang="EN-US">P2P</span>技术，提升<span lang="EN-US">P2P</span>应用的整体性能。<span lang="EN-US"><p></p></span></span></b></font></p><p style="LINE-HEIGHT: 150%;"><font face="宋体"><b style="mso-bidi-font-weight: normal;"><span lang="EN-US" style="FONT-SIZE: 10.5pt; LINE-HEIGHT: 150%;">&nbsp;&nbsp;&nbsp; </span></b><b style="mso-bidi-font-weight: normal;"><span style="FONT-SIZE: 10.5pt; LINE-HEIGHT: 150%;">关键词：对等网络；覆盖层网络；分布式哈希表</span></b></font></p><font face="宋体"><b style="mso-bidi-font-weight: normal;"><span style="FONT-SIZE: 10.5pt; LINE-HEIGHT: 150%;"><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><span lang="EN-US"><font size="3">Abstract2Papplicationsoftwaresinclude file delivery software, Voice over IP (</font><a href="http://www.cww.net.cn/VOIP/" target="_blank"><span style="COLOR: windowtext; TEXT-DECORATION: none; text-underline: none;"><font size="3">VoIP</font></span></a><font size="3">) software, and streaming media software. Because of its various applications, there is still no formed standard for P2P network protocol. The architecture and organization of P2P are also constantly developing. However, network traffic generated by P2P takes a considerable 60%-80% of total traffic. The P2P traffic has the properties of imbalanced distribution, symmetric uploading and downloading, concealment flow, and data concentration. There are many open questions in P2P technology. Firstly, the copyright question is always an uncertainty factor for the development of P2P. Supporting the delivery of legal files at a technical level is an important problem that should be solved. Secondly, security, such as data access security, security routing, account authentication and identity, is another field which should be seriously considered. Moreover, if the uniformed resource location and uniformed routing between P2P applications are realized to form a uniformed development standard, all P2P technologies can be integrated, and the entire performance of P2P applications will improve.<p></p></font></span></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><span lang="EN-US"><font size="3">&nbsp;&nbsp;&nbsp; Keywords2Pnetwork;overlay network; DHT<p></p></font></span></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; P2P</span>应用已经成为互联网的主要应用之一，<span lang="EN-US">P2P</span>的模式也成为许多新型业务的首选模式。<span lang="EN-US">P2P</span>技术被广泛应用于文件共享、网络视频、<span lang="EN-US"><a href="http://www.cww.net.cn/tech/tech.asp?id=179" target="_blank"><span lang="EN-US" style="COLOR: windowtext; TEXT-DECORATION: none; text-underline: none;"><span lang="EN-US">网络电话</span></span></a></span>等领域，以分布式资源共享和并行<span lang="EN-US"><a href="http://www.cww.net.cn/techClass0" target="_blank"><span lang="EN-US" style="COLOR: windowtext; TEXT-DECORATION: none; text-underline: none;"><span lang="EN-US">传输</span></span></a></span>的特点，为用户提供了更多的资源、更高的可用带宽以及更好的服务质量。<span lang="EN-US">P2P</span>节点不依赖中心节点而是依靠网络边缘节点，实现自组织与对等协作的资源发现和共享，因此拥有自组织、可扩展性、鲁棒性、容错性以及负载均衡等优点。<span lang="EN-US">Cachelogic[1]</span>公司的统计数据表明<span lang="EN-US">P2P</span>已经占据了<span lang="EN-US">50%</span>以上的网络带宽，而全球最热门的<span lang="EN-US">P2P</span>文件分发软件<span lang="EN-US">eMule[2]</span>和<span lang="EN-US">BitTorrent[3]</span>产生的流量占了<span lang="EN-US">P2P</span>总流量的<span lang="EN-US">50%</span>以上。此外，<span lang="EN-US">PPLive[4]</span>和<span lang="EN-US">CoolStreaming[5]</span>等实时的流媒体应用发展也极其迅速，用户数目急速增长。可以预见，随着使用<span lang="EN-US">P2P</span>实时流媒体<span lang="EN-US">(P2P-TV)</span>用户数目的迅速增加，在未来因特网业务提供商<span lang="EN-US">(ISP)</span>主干链路的流量中，<span lang="EN-US">P2P</span>实时流媒体应用将占有更大比例。<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><font size="3"><strong><span lang="EN-US" style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体;">&nbsp;&nbsp;&nbsp; 1&nbsp; P2P</span></strong><strong><span style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体;">技术原理</span></strong><b style="mso-bidi-font-weight: normal;"><span lang="EN-US"><p></p></span></b></font></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; P2P</span>应用软件主要有：文件分发软件，如<span lang="EN-US">BitTorrent</span>、<span lang="EN-US">eMule</span>；语音服务软件，如<span lang="EN-US">Skype[6]</span>；流媒体软件，如<span lang="EN-US">PPLive</span>。目前<span lang="EN-US">P2P</span>应用并没有统一的网络协议标准，种类多、形式多样，其体系结构和组织形式也在不断发展。<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; 1.1P2P</span>的体系结构<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; P2P</span>应用按照它的体系结构，可以分成<span lang="EN-US">3</span>代，如图<span lang="EN-US">1</span>所示。<span lang="EN-US"><p></p></span></font></b></p><p align="center" style="LINE-HEIGHT: 150%; TEXT-ALIGN: center;"><b style="mso-bidi-font-weight: normal;"><span lang="EN-US"><shapetype id="_x0000_t75" stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" opreferrelative="t" ospt="75" coordsize="21600,21600"><stroke joinstyle="miter"></stroke><formulas><f eqn="if lineDrawn pixelLineWidth 0"></f><f eqn="sum @0 1 0"></f><f eqn="sum 0 0 @1"></f><f eqn="prod @2 1 2"></f><f eqn="prod @3 21600 pixelWidth"></f><f eqn="prod @3 21600 pixelHeight"></f><f eqn="sum @0 0 1"></f><f eqn="prod @6 1 2"></f><f eqn="prod @7 21600 pixelWidth"></f><f eqn="sum @8 21600 0"></f><f eqn="prod @7 21600 pixelHeight"></f><f eqn="sum @10 21600 0"></f></formulas><path oconnecttype="rect" gradientshapeok="t" oextrusionok="f"></path><lock aspectratio="t" vext="edit"></lock></shapetype><shape id="_x0000_i1025" alt="" type="#_x0000_t75" style="WIDTH: 512.25pt; HEIGHT: 170.25pt;"><imagedata ohref="http://www.cww.net.cn/UpLoadFile/2007/12/27/2007122749258961.gif" src="file:///D:\DOCUME~1\admin\LOCALS~1\Temp\msohtml1\02\clip_image001.gif"><font size="3"><span lang="EN-US" style="FONT-SIZE: 12pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><shapetype id="_x0000_t75" stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" opreferrelative="t" ospt="75" coordsize="21600,21600">&nbsp;<stroke joinstyle="miter"></stroke><formulas><f eqn="if lineDrawn pixelLineWidth 0"></f><f eqn="sum @0 1 0"></f><f eqn="sum 0 0 @1"></f><f eqn="prod @2 1 2"></f><f eqn="prod @3 21600 pixelWidth"></f><f eqn="prod @3 21600 pixelHeight"></f><f eqn="sum @0 0 1"></f><f eqn="prod @6 1 2"></f><f eqn="prod @7 21600 pixelWidth"></f><f eqn="sum @8 21600 0"></f><f eqn="prod @7 21600 pixelHeight"></f><f eqn="sum @10 21600 0"></f></formulas><path oconnecttype="rect" gradientshapeok="t" oextrusionok="f"></path><lock aspectratio="t" vext="edit"></lock></shapetype><img src="file:///D:/Documents%20and%20Settings/admin/Local%20Settings/Temporary%20Internet%20Files/Content.IE5/S927CL2B/2007122749258961%5B1%5D.gif" alt=""/></span></font></imagedata></shape><p></p></span></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; </span>第<span lang="EN-US">1</span>代<span lang="EN-US">P2P</span>应用的是集中控制；第<span lang="EN-US">2</span>代<span lang="EN-US">P2P</span>是一种完全的<span lang="EN-US"><a href="http://www.cww.net.cn/tech/&Icirc;&THORN;&Ouml;&ETH;&ETH;&Auml;&Iuml;&micro;&Iacute;&sup3;" target="_blank"><span lang="EN-US" style="COLOR: windowtext; TEXT-DECORATION: none; text-underline: none;"><span lang="EN-US">无中心</span></span></a></span>的分布式网络；第<span lang="EN-US">3</span>代<span lang="EN-US">P2P</span>是一种混合式的体系结构，同时具备前两代体系结构高效性和容错性的优点。<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; 1.2P2P</span>网络的组织结构<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; P2P</span>网络的组织结构是<span lang="EN-US">P2P</span>体系结构的具体实现。<span lang="EN-US">P2P</span>网络在本质上是无结构，无集中控制的分布式系统，节点通过自组织的<span lang="EN-US">Overlay</span>网络<span lang="EN-US">(</span>覆盖层网络<span lang="EN-US">)</span>来实现文件分发、流媒体以及语音等服务。<span lang="EN-US">Overlay</span>网络的组织方式可以分为有结构和无结构两种<span lang="EN-US">[7]</span>。有结构的<span lang="EN-US">P2P Overly</span>网络是指<span lang="EN-US">Overlay</span>的网络拓扑相对固定，内容的存放也相对有序。有结构的<span lang="EN-US">P2P Overly</span>网络通常使用分布式哈希表<span lang="EN-US">(DHT)</span>来实现，文件存放的位置由文件的唯一标识符决定。无结构的<span lang="EN-US">Overlay</span>网络通过一些松散的规则组织在一起，其文件的存放也表现出很大随机性。<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; <chsdate wst="on" isrocdate="False" islunardate="False" day="30" month="12" year="1899">1.2.1</chsdate></span>有结构的<span lang="EN-US">Overlay</span>网络<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; </span>有结构的<span lang="EN-US">Overlay</span>网络也有很多种不同的实现方法，比较著名的有结构的<span lang="EN-US">Overlay</span>网络包括<span lang="EN-US">Chord[8]</span>、<span lang="EN-US">CAN[9]</span>、<span lang="EN-US">Pastry[10]</span>、<span lang="EN-US">eCAN[11]</span>，下面对<span lang="EN-US">Chord</span>的工作原理进行简单介绍。<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; Chord</span>的原理如下：<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><font size="3"><span lang="EN-US">&nbsp;&nbsp;&nbsp; </span>节点在逻辑上按照标识的大小组成一个环，数据同样有标识并且存放在和自己标识最近的节点上。当在某一个节点上输入查询请求的时候，如果节点的标识小于数据的标识，则向该节点知道的下一个节点请求文件，下一个节点如果拥有该文件则返回结果，否则按前面的方式继续转发给下一个节点。其中每个<span lang="EN-US">Chord</span>节点只需要知道关于部分节点和到达它们的路由信息。<span lang="EN-US">Chord</span>路由查找过程有两个重要特性：每个节点都只需要知道一部分节点的信息，而且离它越近的节点，它就知道越多的关于它们上面的数据信息；每个节点的路由表只有部分节点的路由信息并且不能确定任意一个关键字的确切位置，只能知道下一跳的节点。图<span lang="EN-US">2</span>所示为<span lang="EN-US">Chord</span>节点维护的指针表，其中<span lang="EN-US">N 4</span>代表第<span lang="EN-US">4</span>个节点。<span lang="EN-US"><p></p></span></font></b></p><p style="LINE-HEIGHT: 150%;"><b style="mso-bidi-font-weight: normal;"><span lang="EN-US" style="FONT-SIZE: 12pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><img height="217" src="http://www.cww.net.cn/upLoadFile/2007/12/27/20071227134336734.gif" width="253" border="0" alt=""/></span></b><span lang="EN-US"><p></p></span></p></span></b></font>