Abstract: A method for networking a plurality of the private branch exchange systems is disclosed in which it is possible to both basically exchange information for the networking by using an ISDN line as a private wire in order to connect mutually a plurality of the private branch exchange systems and transmit/receive necessary information between systems by employing D channel with a line signal and an ISDN protocol and designating the specific channel of B channel to a networking private channel for the networking operation. In addition, one or two channels of several channels between a plurality of the private branch exchange systems can be used for exchanging information, so that the exchange of data between systems operating on a network enables expansion of a system and share of common resources, thereby to improve the efficiency of a system.

Abstract: A multiple subscriber implementing method in a key phone system having an integrated service digital network trunk card connected to a digital telephone line, a public switched telephone network trunk card connected to an analog telephone line and an internal memory containing a plurality of logic ports and registered numbers each indicating a corresponding called subscriber terminal, including a call reception routine of connecting an incoming call containing a called subscriber number to a specific port of a corresponding called subscriber terminal when the incoming call is received through the digital telephone line and the called subscriber number corresponds to one of the registered numbers contained in the internal memory; and a call transmission routine of registering a called subscriber number and transmitting an outgoing call when the digital telephone line is seized by a private line subscriber.