PURPOSE: To eliminate a limit in multiplicity of subscriber lines of a remote location on a primary group interface by adopting constitution such that a packet exchange call of an ISDN subscriber line at a remote location corresponds to a packet exchange call on a 23B+D primary rate access interface.

CONSTITUTION: An ISDN subscriber at a remote location is multiplexed once by a remote subscriber accommodation equipment 9 and is connected to an ISDN exchange 21 through primary group interface devices (DTI) 17, 20. The remote subscriber accommodation equipment 9 has layer 1 termination circuits (LT) 10, 12 and layer 2 termination circuits (ET) 11, 13 of ISDN subscriber lines 7, 8, the termination circuits 10, 13 apply D channel demultiplexing in 2B+D channels and the D channel is connected to the termination circuit 11, 12. The primary group interface between the remote subscriber accommodation equipment 9 and the ISDN exchange 21 is a 23B+D interface and the layer 2 termination circuit 18 processing the D channel and L2B47, 48 inserting/ separating the B channel packet to the 23B channels are prepared.