ISDN system with a subscriber line multiplexer for establishing different D-channel links

Claim 1

In an ISDN (Integrated Services Digital Network) system comprising a plurality of subscriber lines associated with a plurality of terminal equipments, a subscriber line multiplexer connected to said plurality of subscriber lines, each of said subscriber lines transmitting a basic TDM (Time Division Multiplex) signal between said plurality of terminal equipments and said subscriber line multiplexer at a basic transmission rate, said terminal equipments having different terminal equipment TEIs (Terminal Endpoint Identifiers) assigned thereto as basic TEIs, respectively, said basic TDM signal comprising a plurality of basic information channels for transmitting information and a basic control channel for transmitting a basic control signal, the basic control signal comprising a specific one of said basic TEIs and control information from a specific one of said terminal equipments, a first ISDN digital switch having a TEI list for registering TEIs, and a high rate transmission line coupling said subscriber line multiplexer and said first ISDN digital switch for transmitting a secondary TDM signal therebetween at a primary transmission rate higher than said basic transmission rate, said primary TDM signal comprising a plurality of primary information channels and a primary control channel, said subscriber line multiplexer statistically multiplexing the basic control channel signals on said plurality of subscriber lines into said primary control channel to thereby transmit said control information to said first ISDN digital switch, wherein said subscriber line multiplexer comprises: a plurality of subscriber interface means coupled to said plurality of subscriber lines, respectively; and internal bus means coupled to said high rate transmission line and commonly connected to said plurality of subscriber interface means; each of said subscriber interfaces comprising: channel separating means coupled with each one of said subscriber lines for separating said basic control channel signal from said basic TDM signal to produce a separated signal; basic TEI list for memorizing said basic TEIs; basic control means responsive to said separated signal for deriving said control information as a derived control information, said basic control means establishing a basic data link between said specific terminal equipment and said basic control means through said basic control channel in cooperation with said basic TEI list; primary control means having a subscriber TEI assigned to said each one of said subscriber line interface means as a primary TEI which is registered in said TEI list as a primary TEI list of said first ISDN digital switch, said primary control means responsive to said derived control information for making a primary control signal which comprises said primary TEI and said derived control information without said specific basic TEI; and transmitting means for transmitting said primary control signal into said primary control channel through said internal bus in the statistical multiplexing fashion so that a primary data link is established between said primary control means and said first ISDN digital switch through said primary control channel in cooperation with said primary TEI list.