To relieve the congestion of interoffice communication and to reduce a maintenance cost by providing a computer module, etc., which has a configuration capable of accessing route set information of an inter-office (inter-station) call which is transmitted from any of central stations or is received by any of the central stations.

Each central station has a computer module(CM) 40 and a TDM exchange 41. The TDM exchange 41 offers a transfer link between a subscriber line and a trunk main line. A digital trunk controller(DTC) 42 connected to the exchange 41 operates as an interface to a public switched telephone network(PSTN) 32. The module 40 has a signaling interface 46 to an ATM backbone network 22 and can perform message transfer with a distributed access MSP(DA-MSP) 48 with it. The DA-MSP 48 functions as an interface to the network 22.