GB1243618A - Pcm switching system - Google Patents

Abstract

1,243,618. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 12 May, 1970 [19 May, 1969], No. 22848/70. Heading H4K. In a computer-controlled, PCM, TDM switching centre, separate switches are provided for the. two directions of transmission each switch being separately addressed from the computer in order to set up a bidirectional transmission. The virtue of switching each direction separately lies in the use of the centre for essentially one sided calls, e.g. data collection from a remote point such as a monitoring point or a computer or a computer peripheral, in radio relay broadcast calls, and in multichannel music transmission. The centre utilizes sixteen, thirty-two channel highways in each direction, of which one highway is reserved for computer originated switching commands while two channels on each highway are utilized for synch. and supervisory signal purposes. Certain outgoing highways from one switch may be connected as incoming highways to the other switch to allow bidirectional transmissions between circuits at a same terminal, but if this is done the essentially non-blocking nature of the switching centre is sacrificed. Both switches may be controlled over a common channel if an interswitch data link is provided and if the switching instructions are accompanied by coded bits indicating the destinations thereof, but a slower system speed is thereby entailed. Free/busy conditions are determined by addressing the memories in a random access made whereas path tracing is effected by cyclic read-out of the memories and comparison of the resultant data with data in the computer.