| 摘要 |
PROBLEM TO BE SOLVED: To provide a communication unit connected to an ISDN that can immediately connect with an opposite party in the case that the communication unit receives an incoming setup message from a caller who is the same opposite party as a called party of a speech during the speech. SOLUTION: The communication unit stores a telephone number of a called party using a 1st channel, and in the case that the communication unit uses the 1st channel to make a speech and receives a setup message arrived in a 2nd channel, the communication unit uses the 2nd channel to identify a caller telephone number sending the setup message, compares the stored called party telephone number with the identified caller number, replies the incoming call using the 2nd channel when the result of comparison indicates coincidence, and connects its speech circuit to the 2nd channel.
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