黑龙江省的数字数据传输网ＤＤＮ黑龙江省邮电设计院杜滨惠一、引言随着经济发展和社会进步，人们对通信的需求不断增加、比如对移动通信以及无线寻呼机漫游的要求，对电话网可靠性的要求，以及对于全新的数据通信的要求等。象金融系统、证券系统、政府、财政、税务部门的... Heilongjiang Province, the digital data transmission network DDN Heilongjiang Institute of Posts and Telecommunications Du Binhui I. Introduction With the economic development and social progress, people continue to increase demand for communications, such as mobile communications and wireless pager roaming requirements of the telephone network reliability Requirements, and new data communications requirements. Like the financial system, securities system, government, finance, tax departments ...