GB1394158A - Processor controlled telecommunication switching system - Google Patents

Abstract

1394158 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 6 March 1973 [6 March 1972] 10718/73 Heading H4K In a processor controlled switching system controlled by at least two processors using a common or duplicate stores storing first status words each indicating the state reached in setting up an associated connection, each processor is arranged upon occurrence of a breakdown in the other of executing a recovery programme which consists of addressing the locations of the first status words in succession, reading the call state as specified in each status word, releasing those calls which have not yet reached the connection stage and for each call in the connection stage to access from store an associated second status word which under normal operation would store the address of the first status word, to compare that address with the address used to access the first status word and in the case of non-identity to release the connection. The arrangement is generally similar to that described in Specification 1,181,184. The first status words are individually associated with corresponding originating junctors and store the identity of the processor handling the call; the connection state reached i.e. idle, dialling, ringing, connection effected and supervision (i.e. one party released but connection not yet released); and have a location for storing the relative address of the associated second status word. The second status words are associated with the terminating junctor circuit and from the moment when that junctor is taken into use store the identity of the processor involved, the type of call (not detailed) and the identity of the associated first status word. The address of the second status word is entered in the associated first status word at this time. The second status word is used to check that the defective processor was working normally when it set up that particular connection. If during the recovery propgramme a first status word indicates that the associated call is in the supervision state then that indication is changed back to the connection state to start again the timing of a period in which the party that has gone on-hook can again lift his receiver to reestablish the connection. The recovery programme is initiated by an external control unit storing that programme on magnetic tape. It may be initiated only when both processors become defective, it being noted that most processor breakdowns are of a temporary nature, the recovery programme being first fed to last processor to become defective and then to the other if it cannot be effected by that processor. A more extensive recovery programme is also provided in the tape unit if the first recovery programme cannot be effected.