论文部分内容阅读
以普通老式电话服务为基础的V.90版本性能速度局限于56kbps,但有多种途径可以突破这一局限而成为高速链路。方法计有ISDN(综合业务数字网)、卫星链路、有线调制解调器、混合式光纤同轴线,以及无线本地回路。但殊途同归,所有这些方法结果没有一个能越过金属线本地回路这个关口。这是电话公司中心运营室与公共电话变换网上终端用户之间不可逾越的“雷池”。这种回路会是安装
Version V.90, which is based on plain old telephone service, is limited to 56kbps, but there are several ways to go beyond this limitation to become a high-speed link. Methods include ISDN (Integrated Services Digital Network), satellite links, cable modems, hybrid fiber coaxial lines, and wireless local loops. But with all the same things, none of these methods result in crossing the local loop of the wire. This is the insurmountable “thunder pool” between the telephone company’s central office and the PSTN terminal subscribers. This circuit will be installed