外文翻譯---數(shù)字網(wǎng)絡(luò)

1、<p><b>　　附錄</b></p><p>　　DIGITAL NETWORK</p><p>　　The ISDN will be a worldwide public telecommunications network that will deliver a wide variety of services. The ISDN will be d

2、efined by the standardization of user interfaces, and will be implemented as a set of digital switches and paths supporting a broad range of traffic types and providing value-added processing services. In practice, there

3、 will be multiple networks, implemented within national boundaries, but from the user’s point of view there will be a single, uniformly accessible worldw</p><p>　　There are two key aspects to ISDN: universal

4、 access and user services. By standardizing the interfaces to ISDN, all ISDN-compatible equipment (e. g. ,telephones computer terminals, personal computers )will be able to attach to the network anywhere in the world and

5、 connect to any other attached system. This can lead to extraordinary flexibility. For example, telephone numbers could be assigned in the same fashion as U.S. social security numbers, good for a lifetime. No matter wher

6、e you lived, or </p><p>　　A digitized network is a prime requirement for integrating a variety of services that the network will support. It is appropriate to view ISDN as being evolutionary in nature and sc

7、ope. The first step in the process toward realizing an ISDN is end-to-end digitization.</p><p>　　Digitization of the telephone network in the United States began in the early 1960s. The early digitized progr

8、am largely addressed the inter exchange transmission system of the metropolitan network. Use of the time division multiplexing technique, rather than the traditional frequency division multiplexing technique, resulted in

9、 an enhanced capacity of the existing telephone plant at minimal cost.</p><p>　　Further development in transmission systems, especially those based on fiberoptic transmission techniques, have pushed the digi

10、tization program well beyond the most optimistic projections made just a few years ago. Compared to other forms of information transport, lightware systems have proved themselves economically and will continue to be the

11、technology of choice in the foreseeable future. Form an initial transmission capability of 45 Mbps ten years ago , the capacity of lightware systems has </p><p>　　ISDN goes much beyond having digital switchi

12、ng and transmission hardware on a ubiquitous basis. The main focus of ISDN is on the support of a wide range of voice and nonvoice or integrated voice/nonvoice applications over the same network. A basic tenet of ISDN is

13、 that this service integration be achieved through a limited set of usernetwork interface arrangements.</p><p>　　Heretofore, private line and switched offerings have been made by telecommunications administr

14、ations using functionally separate networks, for example , are often isolated from one another , and interworking between them is usually a difficult technical issue. ISDN provider for these services within a common fram

15、ework in order to benefit the end users , particularly from the point of view of assuring them, through easy interworking among different services, of the continuing usage of their appli</p><p>　　Recognizing

16、 the continuing growth in digitization of the telecommunications network and the advantages and additional capabilities of an end-to-end digital network , the concept of a single integrated network was born in the 1970s.

17、 Serious efforts were soon started in the CCITT, the organization that establishes international standards for public telecommunications, on a global basis. The first set of standards for ISDN were issued by the CCITT in

18、 1984. As ISDN is established on a global basis, </p><p>　　An integrated access mechanism is a basic tenet of ISDN. The ISDN framework requires that a variety of services be accessed using common access arra

19、ngements with a limited net of access interfaces.</p><p>　　It is easy to recognize that there are very large fixed costs in the global telecommunications network today. Since a large discontinuity in service

20、 features and pricing will be unacceptable in the telecommuni8cations marketplace , it is easy to see that it may be infeasible to move immediately to ISDN in many areas of the world. The full implementation of some ISDN

21、 concepts may take several years, possibly through the whole decade of the 1990s. In the meanwhile , ISDN systems and services will </p><p>　　From a networking perspective, ISDN is a new network infrastructu

22、re that will provide a single point of access to multiple networks and to different kinds of networks. ISDN exchanges will be able to interconnect with each other. In addition, ISDN exchange will be able to connect to ot

23、her existing networks, for example, X.25 packet networks. They will able to connect to other existing voice telephone networks (public not disrupted). There will also interconnect with ensure that the presently avai</

24、p><p>　　Before the advent of ISDN, the premises equipment and network services provide by the common user network were assumed to be distinct elements cooperating in only limited ways in providing an end-to-end

25、 service. The concept of ISDN specifically provides for the extension of network functions into the premises equipment, and vice versa, depending on the need of the application. This requires a rich set of signaling mech

26、anisms between the premises equipment and the network, higher speeds of transm</p><p><b>　　數(shù)字網(wǎng)絡(luò)</b></p><p>　　ISDN是一個(gè)提供各種業(yè)務(wù)的世界范圍的公共電信網(wǎng)絡(luò)。ISDN應(yīng)該由用戶接口標(biāo)準(zhǔn)來定義，并由支持多種通信類型且提供增值處理業(yè)務(wù)的一套數(shù)字交換機(jī)和通路

27、來實(shí)現(xiàn)。事實(shí)上，在國內(nèi)應(yīng)該是各種網(wǎng)絡(luò)，而從用戶的觀點(diǎn)來看又是一個(gè)單一的全球訪問的網(wǎng)絡(luò)。</p><p>　　ISDN有兩個(gè)主要方面：通用呼叫和用戶業(yè)務(wù)。所有與ISDN兼容的設(shè)備（如電話、計(jì)算機(jī)終端、個(gè)人計(jì)算機(jī)）通過對(duì)ISDN接口的標(biāo)準(zhǔn)化，都能在世界任何地方連入網(wǎng)絡(luò)，也可以與其它上網(wǎng)的系統(tǒng)相連，這就有了非常大的靈活性。例如，電話號(hào)碼可以以與美國社會(huì)保險(xiǎn)號(hào)碼相同的形式來分配，從而終生可用。不論居住在哪里或移動(dòng)多么頻繁

28、，只要撥這一永久給你的號(hào)碼總是能接通你的號(hào)碼。</p><p>　　數(shù)字化網(wǎng)絡(luò)是滿足綜合業(yè)務(wù)的基本要求。將ISDN看作是本質(zhì)上的一次革命是很貼切的。實(shí)現(xiàn)ISDN的第一步是端對(duì)端的數(shù)字化。</p><p>　　60年代初期美國的電話網(wǎng)絡(luò)開始數(shù)字化，當(dāng)時(shí)宣布的數(shù)字化方案大都是針對(duì)城市網(wǎng)絡(luò)交換傳輸系統(tǒng)的。采用時(shí)分多路復(fù)用技術(shù)而不是傳統(tǒng)的頻分多路復(fù)用技術(shù)，導(dǎo)致了以最低代價(jià)增強(qiáng)了現(xiàn)有電話系統(tǒng)的能力。

29、</p><p>　　傳輸系統(tǒng)特別是那些基于光纖的傳輸技術(shù)的進(jìn)一步發(fā)展，已將數(shù)字化進(jìn)程大大推動(dòng)了，超出幾年前所做出的最樂觀的估計(jì)。與其它信息傳輸形式相比，光纖系統(tǒng)經(jīng)濟(jì)合理并且在可預(yù)見的未來仍將是首選技術(shù)。光纖系統(tǒng)的傳輸能力從十年前的45Mbps開始，每18個(gè)月翻一番。最近1.8Gbps系統(tǒng)已投入運(yùn)行，到90年代中期2.2Gbps系統(tǒng)將投放商業(yè)市場。在美國端對(duì)斷數(shù)字化還為數(shù)不多，但可望幾年后有很大增長，這是實(shí)現(xiàn)IS

30、DN功能的硬件基礎(chǔ)。</p><p>　　ISDN的發(fā)展已遠(yuǎn)遠(yuǎn)不止是普通應(yīng)用的數(shù)字交換和傳輸硬件。ISDN的主要技術(shù)是在同一個(gè)網(wǎng)絡(luò)上支持話音和非話音或綜合話音/非話音的廣泛應(yīng)用。ISDN的基本宗旨是在通過有限的一組用戶----網(wǎng)絡(luò)接口設(shè)備上實(shí)現(xiàn)其綜合業(yè)務(wù)。</p><p>　　在此之前，電信管理部門用功能上分開的網(wǎng)絡(luò)提供專用和交換功能，盡管它們共享傳輸設(shè)施。例如，電路和分組交換網(wǎng)絡(luò)通常是相

31、互分開的，它們之間的互連通常是一個(gè)技術(shù)難題。ISDN在一個(gè)公共框架內(nèi)提供這些業(yè)務(wù)以便滿足端用戶的需要，特別是通過不同業(yè)務(wù)的簡單互連，確保用戶能夠繼續(xù)使用他們花費(fèi)巨大投資獲得的應(yīng)用軟件。在沒有規(guī)范良好的用戶網(wǎng)絡(luò)接口特性和不能保證使用任何滿足端用戶需要的技術(shù)也可實(shí)現(xiàn)網(wǎng)絡(luò)傳輸功能的情況下，即使沒有另外一些接口問題，ISDN的這些目標(biāo)也不可能實(shí)現(xiàn)。</p><p>　　意識(shí)到電信網(wǎng)絡(luò)數(shù)字化的持續(xù)發(fā)展以及端對(duì)端數(shù)字網(wǎng)絡(luò)的各

32、種優(yōu)點(diǎn)和其他功能之后，70年代產(chǎn)生了單一綜合網(wǎng)絡(luò)的概念。CCITT這個(gè)建立全球性公共電信國際標(biāo)準(zhǔn)的組織很快開始了認(rèn)真的研究，1984年提出了ISDN的第一個(gè)標(biāo)準(zhǔn)集。由于ISDN是建立在全局基礎(chǔ)上的，故可在單一同構(gòu)基礎(chǔ)設(shè)施上提供各種話音和非話音業(yè)務(wù)。模擬通信勢(shì)必消亡，從而導(dǎo)致價(jià)格降低，質(zhì)量提高。ISDN的基本宗旨是有一個(gè)綜合訪問機(jī)構(gòu)，ISDN的主要框架要求使用有限的網(wǎng)絡(luò)訪問接口，通過公共訪問設(shè)備提供各種業(yè)務(wù)。</p><

33、;p>　　顯而易見，現(xiàn)今全球電信網(wǎng)絡(luò)是一個(gè)非常大的固定資產(chǎn)。由于大量的業(yè)務(wù)是斷續(xù)的，而且電信市場的價(jià)格過高也無法接受，因而立即把世界上很多地方的電信設(shè)備換成ISDN顯然是不顯示的。某些ISDN概念的完全實(shí)現(xiàn)業(yè)務(wù)需要紀(jì)念，大概要過了90年代這10年，在此期間ISDN系統(tǒng)和業(yè)務(wù)將與現(xiàn)有的業(yè)務(wù)相互并存。從端用戶業(yè)務(wù)的觀點(diǎn)來看，ISDN是一個(gè)革命性的概念。</p><p>　　從網(wǎng)絡(luò)技術(shù)上看，ISDN是一種全新的、

34、提供從單點(diǎn)訪問多個(gè)并且是不同類型網(wǎng)絡(luò)的結(jié)構(gòu)。ISDN中交換機(jī)之間也能實(shí)現(xiàn)相互聯(lián)機(jī)。另外，ISDN中的交換機(jī)也能連接現(xiàn)有的一些網(wǎng)絡(luò)，如X.25分組網(wǎng)絡(luò)。這些網(wǎng)絡(luò)也可與現(xiàn)有的傳送話音的電話網(wǎng)（公用的和專用的）互連，這些網(wǎng)絡(luò)的互連可以保證在向用戶提供新增加的ISDN業(yè)務(wù)時(shí)，不影響現(xiàn)在已有的業(yè)務(wù)。</p><p>　　在ISDN出現(xiàn)之前，由公共用戶網(wǎng)提供的接入設(shè)備和網(wǎng)絡(luò)業(yè)務(wù)被認(rèn)為時(shí)僅以有限幾種方式合作提供的一種端對(duì)端用戶

35、業(yè)務(wù)的性能各異的不同部件和業(yè)務(wù)。ISDN的概念允許網(wǎng)絡(luò)功能擴(kuò)展上述設(shè)備中，反之亦然，這取決于應(yīng)用的需要。這就要求在這些設(shè)備和網(wǎng)絡(luò)之間有完善的信令機(jī)制，有接入設(shè)備和網(wǎng)絡(luò)業(yè)務(wù)均可支持的更高傳輸速度和一套綜合的端對(duì)端網(wǎng)絡(luò)管理能力。因此在ISDN整個(gè)概念中，所有提供業(yè)務(wù)的部件，不論是基于設(shè)備的還是基于網(wǎng)絡(luò)的，都是使用的，這是與100年以來的實(shí)際是使用的通信業(yè)務(wù)的革命性的區(qū)別。伴隨硬件和軟件技術(shù)的進(jìn)步，現(xiàn)在已經(jīng)有了復(fù)雜的接口，實(shí)現(xiàn)了每秒幾百兆位的