| 摘要 |
PURPOSE:To eliminate the need for an exclusive MODEM selection information transmission section by using a PB signal as MODEM selection information to only install a key telephone dial telephone set on the center thereby backing up a terminal-side MODEM. CONSTITUTION:If the terminal-side MODEM 8 is faulty, the operator of the center side dials a key telephone set 14 to call a MODEM selection information decoding section 17 at the terminal side and the section 17 sends an incoming tone. The center-side operator confirming the tone dials the key telephone set 14 to send the MODEM selection information. When MODEM numbers of the terminal MODEMs 8-10 are denoted by 1-3 respectively, then a key '1' of the telephone set 14 is depressed in switching the MODEM 8. The decoding section 17 decodes the MODEM selection information received by a PB signal and switches the MODEM 8 of the changeover section 18 to the spare MODEM 19.
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