| 摘要 |
PURPOSE:To surely send dial information at end-to-end communication while distinguishing it from control information by supervising a consecutive time of dial information so as to discriminate the control information so as to attain various control by dial operation. CONSTITUTION:When a PB telephone set 4 holds a trunk line call while communicating with a communication party telephone set 1 or hold and transfers the call to other extension connected to a private branch of exchange 3, a dial number for the predetermined holding is depressed for a setting time or over. When the route of trunk lines 2-1, 2-2 are in use, a CPU 9 always retrieves dial information from a PB signal reception circuit 7 and when the dial information '0' is detected, a timer 9-1 is started to supervise the consecution time of said dial information '0' so as to discriminate whether the said consecutive time is less than the set time or below or over. When the time is over the set time, the CPU 9 discriminates the dial information '0' to be holding control information, the start circuit 10 is controlled to activate the holding circuit 5, the telephone trunk lines 2-1, 2-2 are closed in terms of DC to hold the trunk line talking.
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