GB1231563A - - Google Patents

Abstract

1,231,563. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. 29 Jan., 1970 [31 Jan., 1969], No. 5372/69. Heading H4K. In a TDM exchange incorporating a twostage crosspoint switching network, the problem of internal blocking is partially overcome by the provision of overflow links between the " outlets " of the switches in one stage. As shown, the " outlets " of each first stage switch S1 are connected to three group equipments GE while the inlets of the second stage switches S2 are connected to junctors which terminate TDM highways. Each group equipment effects conversion between eight TDM highways of the four wire type and two one-way highways VM1, VM2. The latter each comprise eight wires on which the eight serial PCM bits pertaining to a channel of a both-way highway are transmitted in parallel mode. Each both-way highway carries 24 channels utilizing 8 bit serial PCM. The interstage links IS comprise 16 wires (eight Go and eight Return) and carry 192 channels each of which occupies a time equivalent to 1 PCM bit on a both-way highway. The necessary control circuits for multiplexing the bothway highways on to the one-way highways with or without time slot interchange are not described. In setting up a call from say junctor 3 in the second S2 switch to a both-way highway attached to one of the group equipments in the lowermost S1 switch, a link IS6 is chosen preferentially. If this link is subject to blocking during the required time slot (or in all or nearly all slots, in a system providing time slot interchange) then an overflow route involving say link IS4, switch S1 and overflow link OL1 is selected. It is suggested that the completion of overflow through the group equipment associated with this third S1 switch is accomplished by means of logic circuitry included in the group equipment.