基于P2P的流媒体传输外文文献翻译.doc

外文文献翻译学生姓名：刘海薇 论文题目：基于 p2p 的校园网流媒体平台的设计与实现指导教师：刘大勇 技术职称：副教授原文： peer-to-peer streaming media deliverypeer-to-peer architecture whatever definitions have been put upon it peer-to-peer is an effective rallyingcry for a new way of doing things. many do not consider it a new way it has beenargued that the current interest in peer-to-peer is merely the pendulum swing betweencentralized and decentralized systems. that cycle can be described as : 1. decentralize to remove bottlenecks 2. centralize to increase efficiency nonetheless the particular inflection point of resources available on the internetat this time has allowed peer-to-peer systems to exhibit remarkable scalability andresource exchange. this paper briefly describes a different way of looking at theresources available in these systems it then illustrates the applicability of peer-to-peersystems to content delivery. peer-to-peer is used broadly to describe a variety of network systems thatgenerally run at the presentation session and application layers although ad-hocnetworks and other systems use the same concepts from the physical layer up.specifically peer-to-peer spans content delivery collaboration caching businessprocess automation supply chain management grid computing distributedcomputation business-to-business exchanges data deployment user to usercommunication user communities ad-hoc networks and the internet itself. perhapspeer-to-peer should be considered more of an architectural approach than a specifictechnology or business approach. an way of seeing if a problem is susceptible to a peer-to-peer approach is to ask“if every client in this system could also provide the service they consume wouldthere be a benefit” it is not always the case that there is a benefit many database applicationsrequire centralization for security and simplicity of administration for example.unusual peer-to-peer examples the oft-cited icq and napster are two pioneering peer-to-peer examples. bothprovide an alternative system to dns for naming an attribute of some peer-to-peerdefinitions and both provide the ability for users to directly communicate providingthe “person-to-person” aspect also associated with peer-to-peer. there are however a variety of other systems providing earlier examples of theshift towards peer-to-peer systems. if peer-to-peer is considered as a quality with agradient scale ranging from client-server to a more equilateral power of computingsystems any system that provides a higher ratio of servers to clients could beregarded as peer-to-peer. quake was and remains a 3d online multiplayer video game. quake and laterquakeworld provided a client-server system for synchronized video gaming. theservers were usually high bandwidth high powered systems but due to the demandsof online video gaming so were the clients. and in quake the server was actuallyembedded in the client application blurring the distinction between clients andservers and allowing any node to act by user selection as a client or a server.amongmillions of online quake players there eventually existed tens of thousands of serverson the internet and so the ratio of clients to servers began to even out. shoutcast was designed as a plug-in to a popular mp3 player that enabled livestreaming of mp3 audio over an http connection. users could use shoutcast tocreate a radio station on the internet based on their mp3 collection. this allowedserving from a client application and increased the ease for an end user in configuringthis server.peer-to-peer resources storage cpu bandwidth storage and cpu cycles tend to be the two resources most commonly cited inpeer-to-peer systems. there are however several resources that isolated can be usedto better describe the range of optimizations available through peer-to-peerapproaches. bandwidth is a resource that is transient and non-recapturable. in the same waythat unused airline seats cannot be recaptured as a resource bandwidth whenavailable and unused is lost to time. the first stage of consumer internet expansioninvolved a great disparity between client bandwidth and server bandwidth but asbroadband equalizes this resource it becomes available to a peer-to-peer system. presence latency/proximity presence can be viewed as a resource. when the p in p2p stands for “person”as in instant messaging scenarios presence is the resource of that person beingonline and available for communication at that time. this enables online collaborationbecause it provides at a glance notification of availability. latency and proximity are two relatively unremarked resources that are key tointeractive simulations on the internet. quake provides an example of a large numberof servers quake servers located with an alternative namespace system gamespyand then sorted by latency. the tens of thousands of quake servers provided a pool ofthe service called “quake” but that service was ineffective if the number of hopsbetween the server and the clients or the latency or the packet loss was too high. itwas not the storage space of the machines that was being utilized although it wassome of the cpu cycles but it was the proximity of the server to the client that wasthe precious resource. napster used only megabytes of client-server traffic to manage direct andcontrol terabytes of peer-to-peer traffic. the storage of these peers was notable butthe real feat was offloading the bandwidth requirements to the peers consuming theresources and coordinating their relatively seamless interchange. a centralizednapster would have been technically trivial to implement but prohibitively costly andremarkably difficult to scale. a consistent theme in peer-to-peer systems to date is that they put additionalcode at the client level and thus where it can do different things than if it wascentralized. a strength of peer-to-peer systems is that they distribute code that canprovide services at a more strategic location. for instance some peer-to-peer systemsroute traffic between peers. these servers provide cpu cycles to perform the serviceproximity if the routing algorithm is based on low hop count for instance andbandwidth by providing the routing. this combination of various resources shows why web services now tend to beincluded in discussions of peer-to-peer architectures.content delivery costs the primary resource contention on the internet is over bandwidth. the costs ofbandwidth especially bandwidth with the quality of service goals necessary tosupport online audio and video does not drop as dramatically as the cost of computerhardware. another interesting aspect of bandwidth is that consumers tend to pay a flatfee or a low fee for a moderate amount of broadband bandwidth whereas enterprisetends to pay larger variable costs for their bandwidth. these two factors present an opportunity for systems that can substitute low costhardware into higher value bandwidth or can substitute fixed-cost consumerbandwidth for variable cost enterprise bandwidth. enough large early streaming companies have failed because of theoverwhelming cost of streaming bandwidth. would-be internet “television stations”were technically feasible but completely impractical from a cost standpoint. thesupply chain of internet video in particular is quite broken: content providers areslow to advertise their services because they cannot afford thebandwidth costs of an increased audience. similarly bandwidth providers cater tocustomers who tend not to use their bandwidth. this situation tends tocreateunprofitable shrinking content providers who pay too much for bandwidth theydo not use. this bandwidth need applies to both static web page and dynamicstreaming media content shopping for bandwidth and constraining he costs can bedifficult and can result in highly variable quality of service on the part of contentproviders. this is an opportunity for peer-to-peer technology. 外文文献翻译学生姓名：刘海薇 论文题目：基于 p2p 的校园网流媒体平台的设计与实现指导教师：刘大勇 技术职称：副教授译文： 基于 p2p 的流媒体传输p2p 的构建 无论我们对 p2p 如何定义， 都会作为一个新颖的且行之有效的处理方式 p2p出现在我们面前。许多人并不认同“新颖”这一观点，人们对于 p2p 的兴趣仅仅是在集中的和分散的系统之间摇摆。 这个周期可以描述为： 1. 分别处理，消除瓶颈 2. 集中管理，提高效率 尽管如此，因特网上可用资源的特别拐点，在此时已经使 p2p 系统显示出了明显的延展性和资源互换能力。 本文简要介绍了一种不同以往的看待系统中可用资源的方式，文中还指出 p2p 系统在内容传送方面的适用性。 p2p 技术广泛用于描述各种各样的网络系统，这些网络系统一般运行于显示、会议和应用层面上，尽管自组网以及其他系统在物理层面上应用了相同的概念。特别地，p2p 分为内容传送、协作、缓冲、业务流程自动化、供应链管理、网格计算、分布式计算、用户间交流、数据部署、用户通信、用户社区、自组网和因特网本身。或许 p2p 在构建方面应该考虑更多一些，而不是一个特定的技术或业务。 一方面来看，如果一个问题要用 p2p 来解决，是要问，“如果每个客户在这一系统中还可以提供他们所需的服务，是否能从中获利？” 但是并非总是要求有利可图。例如，许多数据库应用需要集中注意力在管理简易和安全方面。特殊的 p2p 范例 人们常说的 icq 与 napster 就是开创 p2p 先河的两个例子。二者为 dns 提供了替换系统并为之命名， （部分 p2p 定义的一个属性）同时二者还为用户提供直接交流的服务，提供与 p2p 相联系的“人对人”的交流方式。 目前，有各种其他的系统提供较早的关于转向 p2p 系统的例子。如果 p2p被看作从客户服务端到等功率的计算机系统， 那么任何提供更高比率的服务器系统均可视为 p2p。 quake 曾经是（现在仍然是）一种网上流行的三维游戏。quake（以及后来的 quake world ）提供的客户端服务器系统用于同步视频游戏。这些服务器通常是高带宽，高功率系统，但由于网上视频游戏的需求，客户端也是高带宽，高功率的系统。在 quake 中，服务器被嵌入在客户应用中，用以模糊区分客户和服务器，并允许任何节点（由用户选择）被作为客户或服务器。上千万在线的quake 球员中，存在着数以万计的服务器，并开始以相同比例的客户伺服器在互联网中拉平。 shoutcast 是作为一个插件安装在一款受欢迎的 mp3 播放机上，使得流媒体mp3 音频实现多 http 连接。 （在互联网上） 用户可以用 shoutcast 创造一个电台 ，广播自己收藏的 mp3。这项服务允许从客户的应用，以及增加方便的角度，为最终用户配置这个服务器。p2p 资源 存储 cpu 带宽 存储和 cpu 循环往往是 p2p 系统中最常被引用的两种资源。不过，有一些孤立资源，可通过 p2p 方式更好地描述一系列的优化。 带宽是一种瞬时资源，即不可再造的。同理，飞机上的空座位是不能被取回再作资源的。当带宽可以得到且未被使用时，意味着它正在失去时效。消费者网路扩展的第一阶段涉及客户的带宽和服务器带宽，它们之间存在巨大差距，但由于宽带平均分配了这一资源，使之成为 p2p 系统。 拨号 潜伏期/近似性 拨号可以看成是一种资源。当 p2p 中的p做“人”来讲（如在即时通信的情景下）拨号可看作有人在线并可供通信的资源。这使网上协作成为可