The 56k line reference article from the English Wikipedia on 24-Jul-2004
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56k line

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A 56k line is a digital connection (possibly a leased line, possibly switched) capable of carrying 56 kilobits per second (kbit/s). Note that public telephone lines in Canada and the United States cannot carry 56 kbit/s, as CDOC and FCC regulations limit the output power of modems in such a way as to limit throughput to 53 kbit/s, and the practical maximum over real phone lines is closer to 50 kbit/s.

This article was originally based on material from the Free On-line Dictionary of Computing and is used with permission under the GFDL.