GB1163818A - Improvements in or relating to Telecommunications Systems - Google Patents

Abstract

1,163,818. Automatic exchange systems. SIEMENS A.G. 26 May, 1967 [27 May, 1966], No. 24559/67. Heading H4K. In a multi-exchange system having some privileged subscribers who retain their personal directory numbers irrespective of the exchange to which they are currently connected, every exchange includes a store containing the number and present location of these subscribers. If one of the subscribers, e.g. 890, moves to another exchange, e.g. E, the location data in the store at his previous exchange D is modified so as to indicate to which of the exchanges he has moved to. A call to this subscriber from another exchange, e.g. A, is initially routed to his previous exchange in accordance with the unmodified stored data at the calling exchange A and tandem exchange C. From D the "change-of-exchange" data is signalled back to C and A which both update their stores correspondingly. The call to the wanted party may be extended over a junction between D and E or the original connection to D may be broken down and a new connection set-up over the direct junction between A and E. The data in other exchanges, e.g. B, is up-dated whenever these exchanges become involved, either as calling or tandem exchanges, in a call to 890. The interexchange junctions may be TDM highways utilizing pulse-phase or pulse-code modulation or they may be frequency division multiplex junctions. Since the special subscribers are not allotted a specific exchange code-at least so far as their (dialled) directory number is concerned-the calling of such a subscriber involves in effect the features of abbreviated dialling and abbreviated interexchange code transmission. It is suggested that the presentexchange-data for all the subscribers to the system may be stored at each exchange. A highly simplified schematic for the logic required in each exchange is depicted in Fig. 2 (not shown).