2014自考通信英语短文翻译.doc

P27A service is office delivered through a server. The term ”server” has been widely used and accepted in the context of LANs ,although it is an appropriate concept in any network environment .A server contains the hardware, and at least part of the software ,necessary to produce the service. Whether talking about print servers , file servers , communication servers ,or others ,servers usually operate at some point remote from the end-user and are designed for multi-user access to expensive ,complicated ,or infrequently used services.服务常由服务器提供。“服务器”一词已在局域网中广泛地使用和接受，尽管它在任何网络环境中都是一个合适的概念。一个服务器含有产生该服务所必需的硬件，且至少含有部分软件。不论是打印服务器、文件服务器、通信服务器，还是别的什么服务器，服务器都在远离终端用户的某一点工作，并且被设计成使多个用户可以访问那些昂贵的、复杂的或不常使用的服务。P35The goal of your use of the Internet is exchanging message or obtaining information. What you need to know is that you can exchange message with other computers on the Internet and use your computer as a remote terminal on distant computers. But the internal details of the link are less important, as long as it works. If you connect computers together on a network, each computer must have a unique address, which could be either a word or a number. For example, the address of Sams computer could be Sam, or a number.使用Internet的目的是交换消或获得信息。你只须知道你可以与Internet上的其他计算机交换消息并将你的计算机用作远端计算机的远程终端，而链路的内部细节并不太重要，只要网络能工作就行。若将多台计算机连接到网络上，每台计算机须有唯一的地址，地址可以是一个字或一个数字。例如Sam的计算机地址可以是Sam或一个数字。P36Before you can use the Internet, you must choose a way to move data between the Internet and your PC. This link may be a high-speed data communication circuit, a local area network (LAN), a telephone line or a radio channel. Most likely, you will use a Modem attached to your telephone line to talk to the Internet .Naturally, the quality of your Internet connection and service, like many other things in life, is dictated by the amount of money you are willing to spend.在使用Internet 之前，必须使用一种方法在你的PC机和Internet之间传送数据。这种连接的链路可以是高速数据通信电路、局域网（LAN）、电话线路或无线信道。最有可能的是，你使用Modem连到电话线上与Internet 对话。当然，像生活中许多其他的事物一样，与Internet连接和服务的质量是由你所花钱的数量决定的。P43 Improvements in component performance,cost,and reliability by 1980 led to major commitments on the part of telephone companies.Fibre soon became the preferred transmission medium for long-haul trunks.Some early installations 0.8 um light sources and graded-index multimode fibre, but by 1983,designers of intercity links were thinking in terms of 1.3 um,single-mode systems. The single-mode fibere,used in conjunction with a 1.3 um laser,provides a bandwidth advantage which translates into increased repeater spacings for high data rate systems. 到了80年代，光纤器件在性能、价格和可靠性方面的改善使众多电话公司受益匪浅。光纤很快成为长途干线的首选传输媒质。一些早期敷设的光纤线路采用0.8um光源和渐变折射率多模光纤，但到1983年，城市间线路的设计者们就考虑使用1.3um单模光纤系统了。单模光纤与1.3um激光器连接，可以提供宽带特性，增加了高速率系统的中继距离。P43The potential of fibre optics in the other areas is only beginning to be realized. Fibre optic networks for computer systems and offices are becoming more prominent. In the telephone system, the use of fibre optics for interconnecting central offices within a metropolitan area and for lower levels in the swithching hierarchy is still increasing rapidly. Fibre links to the home have been used in demonstration projects. Many observers believe that national telephone systems will eventually be upgraded to handle video bandwidths by using fibre optics. These wideband subscriber loop systems would provide access to services such as picturephone , video entertainment . Widespread installation of these broadband services will become economically feasible.人们对于光纤在其他领域的潜力刚刚开始认识。用于计算机系统和办公室的光纤网络逐渐变得更加重要。在电话系统中，光纤在主要城市地区中心交换局间互联和低级交换中的使用继续迅速增加。入户光缆已经有了示范工程。许多观察家相信，全国电话系统将使用光纤传输视频宽带信号而逐渐升级。这些宽带用户环路系统将为可视电话、视频娱乐节目等业务提供通路。宽带业务广泛使用光纤将会变得经济可行。P60The most basic element is regenerator(shown in Fig.8-4). Youll find regenerators whenever transmission over 50 km is needed. They terminate and regenerate the optical signal. Spacing of regenerators depends on the wavelength being used, the power of the transmitted signal and the receivers sensitivity.Wavelengths of 1310 nm and 1550 nm are preferred because glass fibre is peculiarly transparent to light at these wavelengths. 1550 nm is preferred for long routes because even through the 1550 nm lasers cost more, the fibre is even more transparent at 1550 nm than 1310 nm and so fewer regenerators are needed. 最基本的单元是再生中继器，如图8-4所示，凡传输距离超过50 km时，就需要这一单元。它们终结和再生光信号。再生中继器的间距取决于所用的波长、发送信号的功率以及接收器的灵敏度。人们乐于选用1310 nm和1550 nm的波长，因为玻璃纤维对这些波长的光波尤为透明。对于长距离路由，1550 nm更为可取，尽管1550 nm的激光器价格更高，但因玻璃纤维在该波长下比1310nm波长下更为透明，因而所需的再生中继器更少。P66The transport system adopted in SDH is analogous to a road transport system shown in Fig. 9-1. If you need to deliver items between 2 points you need trucks. Depending on the quantity of items to be moved you need small or large trailers. Depending on the size of the items being shipped you need “pallets” to allow simple stacking within the trailer payload area . For different item types you have different pallets and different loading instructions.SDH采用的传输系统与图9-1（见第109页）所示的公路的运输系统是类似的。假定你想在两地间运送货物，你将需要货车。按照要运送货物的数量，你需要小的或打的车厢。根据被运东西的大小，你需要集装箱，以便在车厢中装货区里能方便地堆放。按照货物类别的不同，你得有不同的集装箱和不同的装堆方法。 P68Section Overhead (SOH) Some signal capacity is allocated in each transport frame for “Section Overhead”.This provides the facilities (such as alarm monitoring and data communications channels ) required to support and transportation of a VC between nodes in a synchronous network. Section overhead pertains only to an individual transport system and is not transferred with the VC between transport systems.ScramblingTo ensure that the clock can always be recovered from the received data, all bytes in the synchronous frame, except those located in the first row of section overhead, are scrambled.段开销（SOH）在每个传输帧中，部分信号容量被分配给段开销。段开销提供了支持和维护同步网络节点间VC的传输所需要的话销（如告警监视、五码监测和数据通信信道等）。段开销仅属于单一传输系统，它不随VC一起在传输系统之间转移。 扰码为确保从接收到的数据中恢复时钟，在同步帧中，除段开销的第一行的字节外，所有字节都被扰码。P75Any communication system which can provide customers with means to communicate from any place , at any time and at any distance gives social and economic advantages . This capability does not exist in many parts of the world . Assuming that it existed , such a system would be limited by the availability of the called person . This person may not be close to his telephone when he / she is called. Urgent communications (police , firemen , hospitals , etc.) which could not be established because of no reply at one end of the link could have dramatic consequences if the delay in response is too long or if the call remain unanswered.任何一种能在任何地方、任何时间，在任意距离内向顾客提供通信的通信系统，都会产生社会及经济的效益，而这种通信能力在世界上许多地方并不存在。假设存在这样的系统，它也会由于能否找到接话人而收到限制。接话人可能在别人给他打电话是不在电话附近。由于线路另一端无回答而不能完成紧急通信（警察、消防人员、医院等），如果延误时间太长或一直没有回音，将会造成严重的后果，因此为这种人提供通信手段是必不可少的。P88Mobile systems originally operated in analogue mode ( and still do ) in the 450 MHzband, moving later to 900 MHz with digital GSM and then to 1800 MHz with personal communications system . The history of mobility can split into generations . The first generation systems were the advanced mobile phone system (AMPS ) in the US, total access communication systems (TACS) in most of Europe and nordic mobile telephone system (NMT) ; which were all analogue systems . The second generation is very much dominated by the standard first set out in Europe by the group special mobile (GSM) committee , which was designed as a global mobile communication system .移动通信系统最初以模拟方式工作（现在仍在运行），其频带在450 MHz，后来逐步发展到900 MHz 的数字GSM系统，下一步是向工作在1800 MHz的个人通信系统发展。移动通信的发展可分为几代。第一代系统如美国的高级移动电话系统（AMPS）、欧洲多数国家的全接入通信系统（TACS）以及北欧的移动电话系统（NMT），这些都是模拟系统。第二代移动通信系统在很大程度上是有欧洲特别移动小组（GSM）委员会所定制的标准决定的，设计这一系统作为全球移动通信系统。P89The third generation mobile communication system currently being developed in Europe is intended to integrate all the different services of second generation systems and cover a much wider range of broadband services ( voice , data , video , and multimedia ) consistent and compatible with technology developments place within the fixed telecommunication networks.目前在欧洲正在开发第三代移动通信系统，其目的是要综合第二代系统的所有不同业务并覆盖更广泛的业务（话音、数据、视频、多媒体）范围，而且还要与固定电信网络的技术发展保持一致和兼容。P111The spread of multimedia users is not just a function of technology,and it is certainly not an unstoppable process.The key to its take-up is in the successful selling of video and television services,which are often gathered under the general title of video-on-demand (VOD)interactive services.A typical VOD architecture takes trunk and access networks into account.The video server is the key to on-demand services.The video server will store a large number of programmes that can be instantly accessed by a large number of individual subscribers,it is stored in a compressed form to save space.多媒体用户的发展不只由技术决定，也绝不是一种一蹴而就的过程。其启动的关键是提供视频和电视业务，这两方面经常合起来统称为视频点播（VOD）交互业务。典型的视频点播网络结构将中继网和接续网都考虑进去了。视频服务器是点播业务的关键。视频服务器可以储存大量的节目，并能使大量的用户立即访问这些节目。为节省储存空间，这些节目常以压缩数据的形式储存。P117By far the largest circuit-switched network is the public telecommunications network the telephone network. This is actually a collection of national networks interconnected to form an international service . Although originally designed and implemented to service analog telephone subscribers , it handles substantial data traffic via modem , and is gradually being converted to a digital network .The public teleco