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在一些国家的长途通信网中,自五、六十年代起,微波无线电接力线路(microwave radio relay line)曾经与电缆和同轴电缆联合一起,成为两大主要支柱。到70年代,卫星通信崛起,但它真正参与国内通信网的比重还不大。进入80年代,光纤通信实用化,数字通信越来越兴旺,有倾向停止新建同轴电缆模拟通信。事实上,市内通信新建的局间线路大多采用光纤光缆,仅用户线仍保留对称电缆。国内通信卫星开始参与边远地
In some countries’ long-distance communications networks, microwave radio relay lines have been co-located with cables and coaxial cables since the 1950s and 1960s and have become the two main pillars. By the 1970s, satellite communications had risen, but its true participation in domestic communications networks was still modest. Into the 80’s, the practical application of optical fiber communications, digital communications more and more prosperous, there is a tendency to stop the new coaxial cable analog communications. In fact, most of the newly established interoffice lines in the city use optical fiber cables, and only the subscriber line still retains the symmetrical cables. Domestic communications satellites began to participate in remote areas