ISDN CHANNEL EXCHANGE SYSTEM AND METHOD FOR CONTROLLING RELIEF OF BUSY CALL IN THE SYSTEM

摘要

PROBLEM TO BE SOLVED: To select a standby system exchange while keeping the connection state of a call to an ISDN channel having been in a speech state on the occurrence of system-down of an active system exchange without interrupting the channel with respect to a PBX exchange system provided with the active system exchange and the standby system exchange. SOLUTION: The active system exchange 141 transfers setup information with respect to a call to an attendant board controller 16 in the case of setup of the call between an ISDN channel and an attendant board 17, and transmits an interruption message to set the ISDN channel into a hold state to the busy ISDN channel on the occurrence of a fault. The attendant board controller 16 controls a changeover circuit 11 to lead the ISDN channel to the standby system exchange 142 on the occurrence of the fault in the active system exchange 141, transmits the setup information transferred from the active system exchange 141 to the standby system exchange 142. The standby system exchange 142 sets a channel between the ISDN channel in a holding state and the attendant board on the basis of the setup information received from the attendant board controller 16 and transmits a restart message to the ISDN channel that is in the holding state to bring the ISDN channel into a speech state.