Test word generator for digital exchanges - is connected onto highway in main switch block for test words to be sent out to loop back at subscriber's line circuit

摘要

The test generator (PG) generates a digital test word and is connected to a central highway (Mux) in the switch block of the exchange (V). The central processor (CPU) control of the exchange (V) initiates the test word from the generator and selects the switching path back to the subscribers' line apparatus (LTA, LTD, ALA) where the test word is looped back to the generator (PG) for evaluation. On analogue exchange lines (LTA) and junctions (ALA) the two wire is open circuited (I/E) so that the test signal is looped back through the two wire/four wire hybrid (GA) into the CODEC in the subscriber's line unit (DTS) or junction term (AS). On digital exchange lines (LTD) the test word is a part of the synchronisation and alignment word sent around the subscriber's loop to the telephone (StD), a digital instrument.