Terminal adapter pooling system for isdn

Abstract

In a key telephone system in which a plurality of data terminals 37l . . . 37n such as personal computers are connected to a key service unit 1 connected to a plurality of ISDNs 23l . . . 23m, a terminal adapter (TA) 41 is pooled so as to be usable in common for the plural data terminals 37l . . . 37n. In response to a setup signal from an ISDN (e.g. 23l), the key service unit 1 selects a single data terminal designated by a subaddress included in the setup signal from among the data terminals 37l . . . 37n, and closes a communication channel between the selected data terminal (e.g. 37l) and the TA 41, so that a status equivalent to that where the selected data terminal 37l and the TA 41 are directly connected to each other can be established. Thereafter, the key service unit 1 transmits a setup signal to the TA 41, and the TA 41 transmits a call to the selected data terminal 37l. When the selected data terminal 37l responds to the call from this TA 41, the key service unit 1 closes a communication channel between the TA 41 and the ISDN 25l, so that a communication link between the selected data terminal 37l and the ISDN 23l can be established via the TA 41. During the process until this communication link can be established, since the selected data terminal 37l and the TA 41 are in the status equivalent to direct coupling, the key service unit 1 is not concerned in the communications between the selected data terminal 37l and thus TA 41, thus reducing the operational load applied to the key service unit 1.