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1、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 th
2、e 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 Internet
3、at 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 u
4、sed 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
5、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 specifictechno
6、logy 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 central
7、ization 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 us
8、ers 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-
9、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. Th
10、eservers 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 c
11、lient 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 conn
12、ection. 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
13、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 ai
14、rline 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 sys
15、tem. 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 gla
16、nce 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.
17、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
18、 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 th
19、e 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
20、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 pee
21、rs. 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
22、.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
23、 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 bandwi
24、dth 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 cos
25、t 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 situa
26、tion 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
27、 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
28、. 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
29、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
30、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 HTT
31、P 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
32、 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能，因为它提供了有效通告。 潜伏期和近似性是两个相对不明显的资源， 然而却是互联网上互动模拟的关键。大量的网络服务器（Quake 服务器）设有其他名字的空间系统（游戏间谍），然后通过潜伏期将其整理，Quake 就是一例。数以万计的 Quake 伺服器提供了大量称为Quake的服务，但是在跳数之间的客户和服务器、或在潜伏期、或丢失数据包的数量太高的话，这种服务就是无效的。它不是存储空间的机器（尽管它是 CPU 的部分循环），但却是最能接近客户的宝贵
33、资源。 Napster 的客户端服务器仅用兆字节的流量来管理，指导和控制兆兆字节的 P2P 流量。这些节点的存放非常显著，但真正的突破在于将带宽需求和节点消耗资源分离开来，并协调了它们相对无缝的交汇处。一个集中的 Napster 已经小心翼翼地走到了一个路口，但是经不起接下来昂贵而艰难的考验。 P2P 系统把更多的代码用于客户端， 一旦集中起来，便可从中做不同的事情。这正是 P2P 永恒的主题。P2P 系统的实力在于，它们分发可以提供服务的代码，这些代码所提供的服务位于更高的战略位置。比如，一些 P2P 系统中节点之间的路由流量。这些服务器提供 CPU 循环（演示服务），近似性（比如路由算法是
34、否基于低跳跃点数），带宽（提供路由）。 各种资源结合在一起，说明了为什么网络服务商现在倾向于将 P2P 构架列入讨论。内容交付费用 最初，因特网上资源争夺的目标是带宽。带宽，尤其是需要支持在线视听的高级服务所需要的带宽，并没有作为计算机硬件成本计算在内。带宽的另一个有趣方面是，消费者往往为适量的宽频带宽支付平价或低于平价的费用，企业往往要为带宽付出较大的可变成本。 这两项因素都为那些可以用低成本的硬件替代价值较高的带宽，或将固定成本消费带宽替换为可变成本企业带宽的系统提供了机会。 早期较大的流媒体公司因为流媒体所需带宽的巨大成本而宣告失败。 实现互联网上“电视台”在技术上是可行的，但从成本这一角度来看则是完全不切实际的。尤其是网络视频的供给链接是相当薄弱的，内容提供商总是缓慢地为他们的服务做广告，因为他们付不起由于观众增加而导致增加的频宽成本。同样，带宽提供商迎合那些不使用其带宽的顾客。 这种情况往往使那些购买过多的带宽却没有使用的供应商收益减少。带宽既要适用于静态形式（网页）也要适用于动态形式（流媒体），购买带宽并控制成本可能会很困难，而且可能给部分供应商带来不同的服务质量。 对于 P2P 技术来说，这是一个机会。
