ISDN user-network interface system

Abstract

An ISDN-user-network interface system comprising an interface buffer and an interface adapter. The interface buffer provided between an ISDN network terminal equipment and a terminal equipment to receive an up-signal frame transmitted from said terminal equipment to said network terminal equipment, to store said up-signal frame, and to transmit said stored up-signal frame at a timing when said network terminal equipment is capable of detecting the synchronization of said up-signal frame. The interface adapter provided between said ISDN network terminal equipment and said terminal equipment, to receive an up-signal frame transmitted from said terminal equipment to said network terminal equipment, to detect D-channel bits of said up-signal frame, to transmit said up-signal frame to said network terminal equipment, to copy said detected D-channel bits into echo channel bits of a down-signal frame from said net-work terminal equipment to said terminal equipment received immediately after the transmission of said up-signal frame, and to transmit said down-signal frame to said terminal equipment.

Dependencies are inferred from the claim text.