| 摘要 |
PURPOSE:To allow an extension subscriber to make a previous arrangement with another extension without sending an unnecessary tone to a trunk line subscriber, by holding a trunk line without holding a calling link. CONSTITUTION:When an extension subscriber TEL engaged with a trunk line CO dials a special number to hold the trunk line CO, a dial tone is sent out of a call-back trunk CBT to the TEL through a trunk-line bothway trunk BWT. At this point of time, the calling link is still held, so the special number is further dialed for complete holding operation. Consequently, while the trunk line CO through the BWT is held, the calling link in a channel switch SW between the TEL and BWT is released to obtain a complete holding state. Therefore, the TEL is connected to another line without any restriction. When reanswering dialing operation is performed for resetting the holding, the TEL and BWT which are held are connected through the switch SW to allow a telephone call again. |
