| 摘要 |
PURPOSE:To prevent an extension from receiving a loud tone, by storing the extension numbers of extensions which are connected to trunks which output high-level signals, for every trunk and by inhibiting bridge cut off for said extensions. CONSTITUTION:Extension EXTA which responded to incoming of central office CO suspends central office CO and performs the operation to call extension EXTB, and the call back connection is performed through call back trunk CBT; and if extension EXTB is busy for the extension other than extension EXTA, the extension number of extension EXTB is stored in trunk CBT. Extension numbers of extensions which output high-level signals of howler trunk HWT are stored in memory device MEM preliminarily; and when extension EXTB is busy, contents stored in trunk HWT and trunk CBT are collated with each other by common control circuit CC, and the bridge cut off for trunks which output high-level signals is inhibited, thereby preventing extensions EXTA and EXTB from receiving a loud tone. |
