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电报是最早出现的电气通信业务,随后又有了电话.在一个多世纪期间,通信网有了很大的发展.用户的模拟电话信号通过模拟的传输和交换设备到达另一用户.这种网路可以称为综合模拟网.它所承担的业务除电话外,也包括传真和采用调制反调制器的电路交换数据等. 60年代出现了数字传输技术,70年代出现了数字交换,到了80年代,采用数字传输和数字交换已成为不可逆转的趋势.综合数字网开始形成. 随着综合数字网的扩大,网路规划者自然会考虑到如何使设备能同时为用户提供多种业务,以充分发挥投资的作用.这就是综合业务数字网(ISDN)形成的原因之一.这里的综合是强调各种话音和非话音业务的综合,这些业务包括普通电话、会议电话、可视电话、电视图像、传真、用户电报、电路交换数据、分组交换数据、交互型电视数据、智能数据终端等.此外,还可提供各种不同带宽,透明的数字通道.
Telegraphs were the first to emerge from the electrical communications business and were followed by telephones. Over more than a century telecommunications networks developed significantly and users’ analogue telephone signals reached another user via analogue transmission and switching equipment. The road can be called an integrated analog network, and the services it undertakes include faxing and circuit-switched data using modulation anti-modulators in addition to telephony, etc. Digital transmission was introduced in the 1960s and digital exchanges occurred in the 1970s. By the 1980s , The use of digital transmission and digital switching has become an irreversible trend.Complex digital network began to form.With the expansion of the integrated digital network, network planners will naturally consider how to make the device can provide users with a variety of business to fully Play the role of investment.This is one of the reasons for the formation of Integrated Services Digital Network (ISDN), the synthesis of which is to emphasize the integration of a variety of voice and non-voice services, including general telephone, conference call, videophone, television images , Fax, subscriber telegraph, circuit switched data, packet switched data, interactive television data, intelligent data terminals, etc. In addition, Different kinds of bandwidth, transparent digital channel.