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全世界接入公用交换网（ＰＳＴＮ）的连接线有６亿条，其中用于本地回路的铜线对占９０％以上。到２０００年，预计这一数字将增长到９亿条，这样就很值得考虑进一步开发现有的铜线基础设施。本文阐述铜线在本地回路中的传统用途，并讨论一些用于改进铜线对传输的新出现的技术。
There are 600 million connections to the Public Switched Telephone Network (PSTN) worldwide, of which over 90% is used for local loops. By the year 2000, this number is expected to grow to 900 million units, making it worthwhile considering the further development of the existing copper infrastructure. This article describes the traditional uses of copper in local loops and discusses some emerging techniques for improving the transmission of copper wires.