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目前使用的传统电信网中,主要有电话网络提供给我们打电话传真服务;分组交换网、数字数据网提供数据通信服务;广播电视网提供广播电视服务。这些专用的电信网络都是为某种专用的业务而设计的,它们的传输速率和信号特性都不相同。每一种网络都需要有专用的物理线路和专用的终端设备,非常不经济。每一种网络都有不同的用户接口标准和接入规程,这使用户感到使用很不方便。
Currently used in the traditional telecommunications network, the main telephone network to provide us with fax services; packet-switched network, digital data network to provide data communications services; radio and television networks to provide radio and television services. These dedicated telecom networks are designed for a specific type of service and have different transmission rates and signal characteristics. Every kind of network needs to have the specialized physical line and the specialized terminal equipment, very uneconomical. Each network has different user interface standards and access procedures, which makes users feel very inconvenient to use.