我国DDN(数字数据网络)网络建设始于上世纪90年代,到目前为止已覆盖全国的绝大部分省市地区,主要为客户提供电路、帧中继、语音／G3传真和虚拟专用网等业务。我国DDN网络规模大、数量多,按地理区域划分为国家骨干网、省DDN和本地网。国家骨干网由设置在各省、自治 China’s DDN (Digital Data Network) network construction began in the 90s of last century, so far covered most of the country’s provinces and cities, mainly to provide customers with circuit, frame relay, voice / G3 fax and VPN services . China’s DDN network is large in scale and large in number, and is divided into a national backbone network, a provincial DDN network and a local network by geographical area. National backbone network set by the provinces, autonomous