Abstract: A data link layer processing (DLLP) system comprises a plurality of in-service DLLPs and a plurality of spare DLLPs. The switching between the in-service DLLP and the spare DLLP is effected by coupling both the DLLPs with the transmission line and transferring logical links from the in-service DLLP to the spare DLLP one by one while frame multiplexing the data from the spare DLLP with the data from the in-service DLLP. After all of the logical links are transferred, a switch decouples the in-service DLLP to leave the spare DLLP coupled with the transmission line for a normal operation.

Abstract: A simple adapter for multiplexing ISDN (Integrated Services Digital Network) terminals adapter for an ISDN basic subscriber access system is connected by a connector to a subscriber's point-to-multipoint bus. The adapter allows a greater number of terminal equipment (TE) to be connected to the point-to-multipoint bus via S/T interfaces. By checking the type, subaddress or the like of a call coming in through the adapter, the adapter is capable of limiting the kind of acceptable calls.

Abstract: An integrated service network ("ISDN") is structured to connect subscriber lines through a packet switching system to incoming or outgoing packet switching calls without passing them through a circuit switching system. This effectively uses the speech path of the circuit switching section instead of using it for packet switching calls. At the same time, the invention minimizes the influence of the introduction of the ISDN upon the software of the circuit switching section. The ISDN digital switching network applies to circuit switching calls which are switched at a local switch and to packet switching calls which are to be switched at a toll switch.