CALLING STATE TRANSFER SWITCH-BACK METHOD IN VoIP PHONE SYSTEM, THE VoIP PHONE SYSTEM, AND PHONE TERMINAL AND SWITCH MANAGEMENT DEVICE FOR THE VoIP PHONE

摘要

PROBLEM TO BE SOLVED: To realize a function of a calling state transfer switchback function, even in a VoIP phone system which is in compliance with the ITU-T recommendation H. 323. SOLUTION: When a switchback operation is detected by a transfer source, before a transfer destination responds to a call after starting a calling state transfer procedure is started, a transfer source transmits a facility message of a switchback request to an IP network. The facility message for indicating a failure of transfer to the transfer destination by the calling state transfer procedure is notified to the transfer source. Furthermore, a speech state by end of transfer is notified by the facility message, to bring a call state to the transfer source and the transfer destination, depending on the switchback operation.