Subscriber connection unit, and switching exchange allowing internet frame concentration

摘要

The subscriber unit (SU) contains 16 cards (ISC1-16) that each connect to 8 ISDN digital communication channels (L1-128). The subscriber cards are controlled by a call handling circuit (CP) within a switching unit (LEC). The subscriber cards concentrate the ISDN digital frames and output onto a single bus in HDLC protocl. They are then routed to either a conventional telephone exchange (PSTN) or directly to a digital network (FRN).