數(shù)字網(wǎng)絡外文翻譯

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</b></p><p>　　ISDN是一個提供各種業(yè)務的世界范圍的公共電信網(wǎng)絡。ISDN應該由用戶接口標準來定義，并由支持多種通信類型且提供增值處理業(yè)務的一套數(shù)字交換機和通路

27、來實現(xiàn)。事實上，在國內(nèi)應該是各種網(wǎng)絡，而從用戶的觀點來看又是一個單一的全球訪問的網(wǎng)絡。</p><p>　　ISDN有兩個主要方面：通用呼叫和用戶業(yè)務。所有與ISDN兼容的設備（如電話、計算機終端、個人計算機）通過對ISDN接口的標準化，都能在世界任何地方連入網(wǎng)絡，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，電話號碼可以以與美國社會保險號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多么頻繁

28、，只要撥這一永久給你的號碼總是能接通你的號碼。</p><p>　　數(shù)字化網(wǎng)絡是滿足綜合業(yè)務的基本要求。將ISDN看作是本質(zhì)上的一次革命是很貼切的。實現(xiàn)ISDN的第一步是端對端的數(shù)字化。</p><p>　　60年代初期美國的電話網(wǎng)絡開始數(shù)字化，當時宣布的數(shù)字化方案大都是針對城市網(wǎng)絡交換傳輸系統(tǒng)的。采用時分多路復用技術而不是傳統(tǒng)的頻分多路復用技術，導致了以最低代價增強了現(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的進一步發(fā)展，已將數(shù)字化進程大大推動了，超出幾年前所做出的最樂觀的估計。與其它信息傳輸形式相比，光纖系統(tǒng)經(jīng)濟合理并且在可預見的未來仍將是首選技術。光纖系統(tǒng)的傳輸能力從十年前的45Mbps開始，每18個月翻一番。最近1.8Gbps系統(tǒng)已投入運行，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，這是實現(xiàn)IS

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

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

32、種優(yōu)點和其他功能之后，70年代產(chǎn)生了單一綜合網(wǎng)絡的概念。CCITT這個建立全球性公共電信國際標準的組織很快開始了認真的研究，1984年提出了ISDN的第一個標準集。由于ISDN是建立在全局基礎上的，故可在單一同構(gòu)基礎設施上提供各種話音和非話音業(yè)務。模擬通信勢必消亡，從而導致價格降低，質(zhì)量提高。ISDN的基本宗旨是有一個綜合訪問機構(gòu)，ISDN的主要框架要求使用有限的網(wǎng)絡訪問接口，通過公共訪問設備提供各種業(yè)務。</p><

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

34、提供從單點訪問多個并且是不同類型網(wǎng)絡的結(jié)構(gòu)。ISDN中交換機之間也能實現(xiàn)相互聯(lián)機。另外，ISDN中的交換機也能連接現(xiàn)有的一些網(wǎng)絡，如X.25分組網(wǎng)絡。這些網(wǎng)絡也可與現(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)絡的互連可以保證在向用戶提供新增加的ISDN業(yè)務時，不影響現(xiàn)在已有的業(yè)務。</p><p>　　在ISDN出現(xiàn)之前，由公共用戶網(wǎng)提供的接入設備和網(wǎng)絡業(yè)務被認為時僅以有限幾種方式合作提供的一種端對端用戶

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