| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to use an exchange device independently of the system of a line to be used. SOLUTION: A key telephone system 10 has a function for superposing a specific bit pattern to a channel B and sending the bit pattern at the idle time of a digital line. A time switch 32 extracts an idle pattern 52 from an idle channel in an ISDN network under the control of a CPU 30 and superposes the idle pattern 52 to an idle channel B in an output data stream 41 to send it.
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