GB1162484A - Unit for Selective Blocking of Subscribers for Telephone Exchanges. - Google Patents

Abstract

1,162,484. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 4 April, 1968 [8 April, 1967], No. 16165/68. Heading H4K. In a telephone system a common store stores the telephone numbers of subscribers between which called must be blocked, and for each call the store is interrogated for the stored combination of the calling and called numbers. A stepby-step system and a register controlled system are outlined. The store is divided up into sections, each of which may be permanently associated with a subscriber and have an address corresponding to the subscriber's telephone number, or may store theidentity of the subscriber with which it is at present associated with. In either case the store is adapted to block either incoming or outgoing calls in that it stores the numbers of other subscribers to or from which calls should be blocked. These may be the complete designations of individual subscribers or the common digits (e.g. the exchange designation) of groups of subscribers, the remaining digit spaces being filled with special signals. During the establishment of a call the store is interrogated for a storage section associated with either subscriber to be involved in a call and if such a section is found the subscriber and/or group designations in that section are read out sequentially under the control of a counter and compared with the number of the other subscriber involved in a call. In the event of a match being found, the call is blocked and a characteristic tone is transmitted to the calling subscriber.