To complete update work simply by updating only the direct inward dialling table of a corresponding private branch exchanger, when changing the correspondence relationship between an extension number at a telephone terminal under partial private branch exchangers and a direct inward dialling number in a private branch exchange system having a plurality of private branch exchangers, and to loosen restrictions in the capacity of the direct inward dialling table to operability and expandability in the system.
When incoming to a direct inward dialing trunk accommodated by the private branch exchange A, incoming information on the incoming is acquired and is transmitted to other private branch exchangers. Other private branch exchangers determine whether the incoming is the incoming of the terminal destination under own private branch exchanger based on the incoming information. The private branch exchanger B that determines that the incoming is the incoming of the terminal destination under own private branch exchanger responds to the private branch exchanger A. The connection of a terminal according to the incoming information is established via the private branch exchangers A and B.
Shuichi Fukuda
Takashi Sasaki
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