基于p2p的流媒體傳輸外文文獻(xiàn)翻譯

1、<p><b>　　外文文獻(xiàn)翻譯</b></p><p><b>　　原文：</b></p><p>　　Peer-to-Peer Streaming Media Delivery</p><p>　　Peer-to-Peer Architecture</p><p>　　Whatever

2、 definitions have been put upon it, peer-to-peer is an effective rallying cry for a new way of doing things. Many do not consider it a new way; it has been argued that the current interest in peer-to-peer is merely the p

3、endulum swing between centralized and decentralized systems.</p><p>　　That cycle can be described as :</p><p>　　1. Decentralize to remove bottlenecks</p><p>　　2. Centralize to incre

4、ase efficiency</p><p>　　Nonetheless, the particular inflection point of resources available on the Internet at this time has allowed peer-to-peer systems to exhibit remarkable scalability and resource exchan

5、ge. This paper briefly describes a different way of looking at the resources available in these systems; it then illustrates the applicability of peer-to-peer systems to content delivery.</p><p>　　Peer-to-pe

6、er is used broadly to describe a variety of network systems that generally run at the presentation, session, and application layers, although ad-hoc networks and other systems use the same concepts from the physical laye

7、r up. Specifically, peer-to-peer spans content delivery, collaboration, caching, business process automation, supply chain management, grid computing, distributed computation, business-to-business exchanges, data deploym

8、ent, user to user communication, user communities,</p><p>　　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 t

9、hey consume, would there be a benefit?”</p><p>　　It is not always the case that there is a benefit; many database applications require centralization for security and simplicity of administration, for exampl

10、e. </p><p>　　Unusual Peer-to-Peer Examples</p><p>　　The oft-cited ICQ and Napster are two pioneering peer-to-peer examples. Both provide an alternative system to DNS for naming, (an attribute of

11、 some peer-to-peer definitions ) and both provide the ability for users to directly communicate, providing the “person-to-person” aspect also associated with peer-to-peer.</p><p>　　There are, however, a vari

12、ety of other systems providing earlier examples of the shift towards peer-to-peer systems. If peer-to-peer is considered as a quality with a gradient scale, ranging from client-server to a more equilateral power of compu

13、ting systems, any system that provides a higher ratio of servers to clients could be regarded as peer-to-peer.</p><p>　　Quake was (and remains) a 3d online multiplayer video game. Quake (and later QuakeWorld

14、) provided a client-server system for synchronized video gaming. The servers were usually high bandwidth, high powered systems, but due to the demands of online video gaming, so were the clients. And in Quake, the server

15、 was actually embedded in the client application, blurring the distinction between clients and servers and allowing any node to act (by user selection) as a client or a server.Among millions of</p><p>　　Shou

16、tCast was designed as a plug-in to a popular MP3 player that enabled live streaming of MP3 audio over an HTTP connection. Users could use ShoutCast to create a radio station (on the Internet) based on their MP3 collectio

17、n. This allowed serving from a client application, and increased the ease for an end user in configuring this server.</p><p>　　Peer-to-peer Resources</p><p><b>　　Storage</b></p>

18、;<p><b>　　CPU</b></p><p>　　Bandwidth </p><p>　　Storage and CPU cycles tend to be the two resources most commonly cited in peer-to-peer systems. There are, however, several res

19、ources that, isolated, can be used to better describe the range of optimizations available through peer-to-peer approaches.</p><p>　　Bandwidth is a resource that is transient and non-recapturable. In the sam

20、e way that unused airline seats cannot be recaptured as a resource, bandwidth, when available and unused, is lost to time. The first stage of consumer Internet expansion involved a great disparity between client bandwidt

21、h and server bandwidth, but as broadband equalizes this resource, it becomes available to a peer-to-peer system.</p><p><b>　　Presence</b></p><p>　　Latency/Proximity </p><p

22、>　　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 being online and available for communication at that time.

23、This enables online collaboration because it provides at a glance notification of availability. </p><p>　　Latency and proximity are two relatively unremarked resources that are key to interactive simulations

24、 on the Internet. Quake provides an example of a large number of servers (Quake servers) located with an alternative namespace system (GameSpy) and then sorted by latency. The tens of thousands of Quake servers provided

25、a pool of the service called “Quake”, but that service was ineffective if the number of hops between the server and the clients, or the latency, or the packet loss, was too high. </p><p>　　Napster used only

26、megabytes of client-server traffic to manage, direct, and control terabytes of peer-to-peer traffic. The storage of these peers was notable, but the real feat was offloading the bandwidth requirements to the peers consum

27、ing the resources and coordinating their relatively seamless interchange. A centralized Napster would have been technically trivial to implement, but prohibitively costly and remarkably difficult to scale. </p>&l

28、t;p>　　A consistent theme in peer-to-peer systems to date is that they put additional code at the client level and thus where it can do different things than if it was centralized. A strength of peer-to-peer systems is

29、 that they distribute code that can provide services at a more strategic location. For instance, some peer-to-peer systems route traffic between peers. These servers provide CPU cycles (to perform the service), proximity

30、 (if the routing algorithm is based on low hop count for instance), a</p><p>　　This combination of various resources shows why web services now tend to be included in discussions of peer-to-peer architecture

31、s. </p><p>　　Content Delivery Costs</p><p>　　The primary resource contention on the Internet is over bandwidth. The costs of bandwidth, especially bandwidth with the quality of service goals nec

32、essary to support online audio and video, does not drop as dramatically as the cost of computer hardware. Another interesting aspect of bandwidth is that consumers tend to pay a flat fee or a low fee for a moderate amoun

33、t of broadband bandwidth, whereas enterprise tends to pay larger, variable costs for their bandwidth.</p><p>　　These two factors present an opportunity for systems that can substitute low cost hardware into

34、higher value bandwidth, or can substitute fixed-cost consumer bandwidth for variable cost enterprise bandwidth. </p><p>　　Enough large, early streaming companies have failed because of the overwhelming cost

35、of streaming bandwidth. Would-be Internet “television stations” were technically feasible but completely impractical from a cost standpoint. The supply chain of Internet video in particular is quite broken: Content provi

36、ders are slow to advertise their services because they cannot afford the</p><p>　　bandwidth costs of an increased audience. Similarly, bandwidth providers cater to customers who tend not to use their bandwid

37、th. This situation tends to createunprofitable, shrinking content providers who pay too much for bandwidth they do not use. This bandwidth need applies to both static (web page) and dynamic (streaming media) content; sho

38、pping for bandwidth and constraining he costs can be difficult and can result in highly variable quality of service on the part of content providers. </p><p>　　This is an opportunity for peer-to-peer techno

39、logy. </p><p><b>　　外文文獻(xiàn)翻譯</b></p><p><b>　　譯文：</b></p><p>　　基于P2P的流媒體傳輸</p><p><b>　　P2P的構(gòu)建</b></p><p>　　無論我們對(duì)P2P如何定義，P2P

40、都會(huì)作為一個(gè)新穎的且行之有效的處理方式出現(xiàn)在我們面前。許多人并不認(rèn)同“新穎”這一觀點(diǎn)，人們對(duì)于P2P的興趣僅僅是在集中的和分散的系統(tǒng)之間搖擺。</p><p>　　這個(gè)周期可以描述為：</p><p><b>　　分別處理，消除瓶頸</b></p><p><b>　　集中管理，提高效率</b></p>&l

41、t;p>　　盡管如此，因特網(wǎng)上可用資源的特別拐點(diǎn)，在此時(shí)已經(jīng)使P2P系統(tǒng)顯示出了明顯的延展性和資源互換能力。本文簡(jiǎn)要介紹了一種不同以往的看待系統(tǒng)中可用資源的方式，文中還指出P2P系統(tǒng)在內(nèi)容傳送方面的適用性。</p><p>　　P2P技術(shù)廣泛用于描述各種各樣的網(wǎng)絡(luò)系統(tǒng)，這些網(wǎng)絡(luò)系統(tǒng)一般運(yùn)行于顯示、會(huì)議和應(yīng)用層面上，盡管自組網(wǎng)以及其他系統(tǒng)在物理層面上應(yīng)用了相同的概念。特別地，P2P 分為內(nèi)容傳送、協(xié)作、緩沖、

42、業(yè)務(wù)流程自動(dòng)化、供應(yīng)鏈管理、網(wǎng)格計(jì)算、分布式計(jì)算、用戶間交流、數(shù)據(jù)部署、用戶通信、用戶社區(qū)、自組網(wǎng)和因特網(wǎng)本身?；蛟SP2P在構(gòu)建方面應(yīng)該考慮更多一些，而不是一個(gè)特定的技術(shù)或業(yè)務(wù)。</p><p>　　一方面來看，如果一個(gè)問題要用P2P來解決，是要問，“如果每個(gè)客戶在這一系統(tǒng)中還可以提供他們所需的服務(wù)，是否能從中獲利？” </p><p>　　但是并非總是要求有利可圖。例如，許多數(shù)據(jù)庫應(yīng)用需

43、要集中注意力在管理簡(jiǎn)易和安全方面。</p><p><b>　　特殊的P2P范例</b></p><p>　　人們常說的ICQ與Napster就是開創(chuàng)P2P先河的兩個(gè)例子。二者為DNS提供了替換系統(tǒng)并為之命名，（部分P2P定義的一個(gè)屬性）同時(shí)二者還為用戶提供直接交流的服務(wù)，提供與P2P相聯(lián)系的“人對(duì)人”的交流方式。 </p><p>　　目前，

44、有各種其他的系統(tǒng)提供較早的關(guān)于轉(zhuǎn)向P2P系統(tǒng)的例子。如果P2P被看作從客戶服務(wù)端到等功率的計(jì)算機(jī)系統(tǒng)，那么任何提供更高比率的服務(wù)器系統(tǒng)均可視為P2P。</p><p>　　Quake曾經(jīng)是（現(xiàn)在仍然是）一種網(wǎng)上流行的三維游戲。Quake（以及后來的Quake world ）提供的客戶端—服務(wù)器系統(tǒng)用于同步視頻游戲。這些服務(wù)器通常是高帶寬，高功率系統(tǒng)，但由于網(wǎng)上視頻游戲的需求，客戶端也是高帶寬，高功率的系統(tǒng)。在Qu

45、ake中，服務(wù)器被嵌入在客戶應(yīng)用中，用以模糊區(qū)分客戶和服務(wù)器，并允許任何節(jié)點(diǎn)（由用戶選擇）被作為客戶或服務(wù)器。上千萬在線的Quake球員中，存在著數(shù)以萬計(jì)的服務(wù)器，并開始以相同比例的客戶伺服器在互聯(lián)網(wǎng)中拉平。 </p><p>　　Shoutcast是作為一個(gè)插件安裝在一款受歡迎的MP3播放機(jī)上，使得流媒體MP3音頻實(shí)現(xiàn)多 HTTP連接。用戶可以用Shoutcast創(chuàng)造一個(gè)電臺(tái)（在互聯(lián)網(wǎng)上），廣播自己收藏的MP3

46、。這項(xiàng)服務(wù)允許從客戶的應(yīng)用，以及增加方便的角度，為最終用戶配置這個(gè)服務(wù)器。</p><p><b>　　P2P資源</b></p><p><b>　　存儲(chǔ)</b></p><p><b>　　CPU</b></p><p><b>　　帶寬</b><

47、;/p><p>　　存儲(chǔ)和CPU循環(huán)往往是P2P系統(tǒng)中最常被引用的兩種資源。不過，有一些孤立資源，可通過P2P方式更好地描述一系列的優(yōu)化。</p><p>　　帶寬是一種瞬時(shí)資源，即不可再造的。同理，飛機(jī)上的空座位是不能被取回再作資源的。當(dāng)帶寬可以得到且未被使用時(shí)，意味著它正在失去時(shí)效。消費(fèi)者網(wǎng)路擴(kuò)展的第一階段涉及客戶的帶寬和服務(wù)器帶寬，它們之間存在巨大差距，但由于寬帶平均分配了這一資源，使之

48、成為P2P系統(tǒng)。</p><p><b>　　撥號(hào)</b></p><p><b>　　潛伏期/近似性</b></p><p>　　撥號(hào)可以看成是一種資源。當(dāng)P2P中的‘p’做“人”來講（如在即時(shí)通信的情景下）撥號(hào)可看作有人在線并可供通信的資源。這使網(wǎng)上協(xié)作成為可能，因?yàn)樗峁┝擞行ǜ妗?lt;/p><p

49、>　　潛伏期和近似性是兩個(gè)相對(duì)不明顯的資源，然而卻是互聯(lián)網(wǎng)上互動(dòng)模擬的關(guān)鍵。大量的網(wǎng)絡(luò)服務(wù)器（Quake服務(wù)器）設(shè)有其他名字的空間系統(tǒng)（游戲間諜），然后通過潛伏期將其整理，Quake就是一例。數(shù)以萬計(jì)的Quake伺服器提供了大量稱為"Quake"的服務(wù)，但是在跳數(shù)之間的客戶和服務(wù)器、或在潛伏期、或丟失數(shù)據(jù)包的數(shù)量太高的話，這種服務(wù)就是無效的。它不是存儲(chǔ)空間的機(jī)器（盡管它是CPU的部分循環(huán)），但卻是最能接近客戶的

50、寶貴資源。</p><p>　　Napster的客戶端—服務(wù)器僅用兆字節(jié)的流量來管理，指導(dǎo)和控制兆兆字節(jié)的P2P流量。這些節(jié)點(diǎn)的存放非常顯著，但真正的突破在于將帶寬需求和節(jié)點(diǎn)消耗資源分離開來，并協(xié)調(diào)了它們相對(duì)無縫的交匯處。一個(gè)集中的Napster已經(jīng)小心翼翼地走到了一個(gè)路口，但是經(jīng)不起接下來昂貴而艱難的考驗(yàn)。</p><p>　　P2P系統(tǒng)把更多的代碼用于客戶端，一旦集中起來，便可從中做不

51、同的事情。這正是P2P永恒的主題。P2P系統(tǒng)的實(shí)力在于，它們分發(fā)可以提供服務(wù)的代碼，這些代碼所提供的服務(wù)位于更高的戰(zhàn)略位置。比如，一些P2P系統(tǒng)中節(jié)點(diǎn)之間的路由流量。這些服務(wù)器提供CPU循環(huán)（演示服務(wù)），近似性（比如路由算法是否基于低跳躍點(diǎn)數(shù)），帶寬（提供路由）。</p><p>　　各種資源結(jié)合在一起，說明了為什么網(wǎng)絡(luò)服務(wù)商現(xiàn)在傾向于將P2P構(gòu)架列入討論。</p><p><b&g

52、t;　　內(nèi)容交付費(fèi)用</b></p><p>　　最初，因特網(wǎng)上資源爭(zhēng)奪的目標(biāo)是帶寬。帶寬，尤其是需要支持在線視聽的高級(jí)服務(wù)所需要的帶寬，并沒有作為計(jì)算機(jī)硬件成本計(jì)算在內(nèi)。帶寬的另一個(gè)有趣方面是，消費(fèi)者往往為適量的寬頻帶寬支付平價(jià)或低于平價(jià)的費(fèi)用，企業(yè)往往要為帶寬付出較大的可變成本。</p><p>　　這兩項(xiàng)因素都為那些可以用低成本的硬件替代價(jià)值較高的帶寬，或?qū)⒐潭ǔ杀鞠M(fèi)帶

53、寬替換為可變成本企業(yè)帶寬的系統(tǒng)提供了機(jī)會(huì)。</p><p>　　早期較大的流媒體公司因?yàn)榱髅襟w所需帶寬的巨大成本而宣告失敗。實(shí)現(xiàn)互聯(lián)網(wǎng)上“電視臺(tái)”在技術(shù)上是可行的，但從成本這一角度來看則是完全不切實(shí)際的。尤其是網(wǎng)絡(luò)視頻的供給鏈接是相當(dāng)薄弱的，內(nèi)容提供商總是緩慢地為他們的服務(wù)做廣告，因?yàn)樗麄兏恫黄鹩捎谟^眾增加而導(dǎo)致增加的頻寬成本。同樣，帶寬提供商迎合那些不使用其帶寬的顧客。這種情況往往使那些購買過多的帶寬卻沒有使用