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引 言 通信网由用户系统、传输系统和交换系统三部分构成。自六十年代以来,PCM时分制传输技术得到迅速发展,使链路传输得以数字化。数字程控交换机的问世,实现了数字信号的时分交换。这就使得传输系统和交换系统都可用PCM方式构成。把两者统一起来,从而提高了通信系统的效率和可靠性。数字传输系统和数字交换系统连接起来构成了综合数字网(IDN)。用于传输电话业务的综合数字网称为电话IDN。在电话IDN中,用户系统仍然
Introduction Communication network by the user system, transmission system and switching system consists of three parts. Since the 1960s, PCM time division transmission technology has been rapidly developed, so that the link transmission can be digitized. The advent of digital program-controlled switches to achieve the time-sharing digital signals. This makes the transmission system and switching system can be PCM form. Unify the two, thus improving the efficiency and reliability of the communication system. Digital transmission systems and digital switching systems are linked to form an integrated digital network (IDN). An integrated digital network for the transmission of telephone services is called a telephone IDN. In the phone IDN, the user’s system is still