End-to-end call processing of an ISDN-BRI central-office switch is simulated using a polled multi-tasking method which is executed by a single microcomputer in an ISDN-BRI central-office emulator which includes (i) a packet handler, (ii) a time-space multiplexer, (iii) an in-band tone generator,...http://www.google.com/patents/US5805570?utm_source=gb-gplus-sharePatent US5805570 - Method of simulating an ISDN-BRI central office switch using a single microcomputer 
