GB1459868A - Centrally controlled telecommunications exchange systems - Google Patents

Abstract

1459868 Automatic exchange systems SIEMENS AG 25 Jan 1974 [30 Jan 1973] 03456/74 Heading H4K In an exchange in which a single scanner is used to scan all the exchange circuits having network appearances means are provided whereby different types of circuit are assigned different priorities. The exchange is a PBX having a known switching network arranged according to the revised trunking scheme and wherein the number of switching stages through which a connection is established depends on the network appearances of the subscribers. All requests for service are initiated by a SPC processor P which has access to the exchange circuits via priority circuits which are each coupled to all the exchange circuits having a respective priority. Hence if the processor requires a scan to be made to identify any circuits of a particular priority which may be free for use, or are in a calling condition it sends a signal to the corresponding priority circuit which causes a mark to be extended to all the circuits of the corresponding priority. The scanner is then caused to scan all the exchange circuits to identify all the circuits with the particular priority requiring attention. Some exchange circuits may be assigned two different priorities by coupling them to two different priority circuits, e.g. main exchange junctions seized in an incoming direction require more urgent attention than junctions seized in an outgoing direction. To this end, the processor responds to a service request from a main exchange junctor to send a signal to a first priority circuit which causes all exchange junctors seized in the incoming direction that require attention to extend a request to the scanner. Subsequent to this scan, the processor enables a second priority circuit to cause all exchange junctors seized in the outgoing direction that require attention to issue a request to the scanner. Different subscribers may be assigned different priorities. There is also described an arrangement for selecting a free register which is closest, in terms of the length of the switching network path required, to the calling subscriber, this part of the discription being substantially the same as that of Specification 1,453,518.