Patent GB-1181182-A (GB)
Title: Automatic Telecommunication Switching System and Information Handling System
IPC: H04Q3/545
Filed: 1968-01-11
Abstract: 1,181,182. Multi-processor computing systems. INTERNATIONAL STANDARD ELECTRIC CORP. 11 Jan., 1968 [23 Jan., 1967], No. 1733/68. Heading G4A. [Also in Divisions H3-H5] Two or more programme controlled processors operate concurrently to process connections in a telephone exchange network each processor acquainting the other processor or processors with details of the work it has in hand so that the work of each processor is kept separate and so that in the event of a fault in a processor it may be put out of service and responsibility for the connections under its control be transferred to another processor. As specifically described two processors, CPA and CPB, control a switching network comprised of n modules PM1 to PMn. Each module has a separate set of control circuits for each processor. Thus module PM1 comprising network SN1 has a scanner SCA1, a tester-marker-driver TMDA1 and an interfacial or peripheral register PRA1, whereby the network may be controlled by processor CPA over bus BA common to all modules. Corresponding circuits SCB1, TMDB1, and PRB1, are provided whereby the network can be controlled by processor CPB over lens BB. The scanners SC work in synchronism with the processors as and when network conditions need to be determined. The testermarker-drivers TMD contain registers for processor commands which they carry out in their own time, which is to say asynchronously with respect to the processors. Data is transmitted between the processors over channels a, b, containing inter-processor registers IRAB, IRBA. The data transmitted from one processor to the other in respect of each connection comprises the equipment number of a line formed in the calling state and not given service by the other processor; the identity of a junctor seized for a connection; the equipment number of the called line; a code indicating that the call is in the ringing phase; a code indicating that the call is in the conversation phase; and the junctor identity to indicate when this is released to break down the connection. Processor malfunction.-If the number of connections served by one processor falls substantially and consistently below the number of connections served by the other, the lagging processor is put out of service. To judge the situation a count is taken of the number of items of information sent from each processor to the other. An item of information sent from CPA to CPB steps a unidirectional counter CA and a reversible counter RC in one direction. Similarly, an item of information sent from CPB to CPA steps unidirectional counter CB and the reversible counter RC in the other direction. If either CA or CB reach a count of 1024 before RC wanders from its centre point by as much as 256 in either direction, all the counters are set to zero to start a fresh period of supervision. If RC deviates as much as 256 before CA or CB reach 1024, a bi-stable BSA or BSB corresponding to the processor of low activity is set and this in turn sets a bi-stable PA00 or PB00 in one processor to indicate that the other is being put out of service. When put back into service a processor on lead k or l, resets the bi-stables. Test points in each processor and in the network control circuits are examined in the course of a base level maintenance programme and a fault detected by this means produces a signal on lead m or n to set the bi-stable BSA or BSB. When by means of the bi-stable PA00 or PB00 one processor finds that the other is put out of service it examines its record of connections signalled as under control of the other processor and takes over fully only those connections in the conversation phase. Connections in any other phase of development are taken over only for the purpose of effecting their immediate release. Main processor circuits.-Each processor has a number of buffers, which store variable data in addresses rigidly associated with network and processor devices, and a number of hoppers which store variable items of information in a queue pending the appropriate programmed treatment. Junctor status buffers are provided for each junctor and indicate which processor serves the connection using the junctor, the phase to which the connection has progressed, and the address and type of register currently in service. Line input buffers each serve a line and indicate the state of the line loop and cut-off relay. Junctor input buffers, one for each junctor, indicate the state of the loop between junctor and subscriber. Register buffers have a time counter, a pulse counter and a digit counter, and record the calling line equipment number, called line directory or equipment number, and junctor address, as well as recording a sequence bit and bits to indicate whether the timer should time at a low or a high rate. Register buffers supervise a call up to the point of ringing, the phase of a connection from ringing to reply being supervised by an auxiliary register buffer which effects timing and records the address of the junctor employed for the connection. Buffers are also provided for supervising release of a connection, for recording the address of the register in service for a transaction between a processor and a tester-marker-driver, and for recording a clock-interrupt message from the other processor. Hoppers are provided to store the equipment number of originating calls, to store the equipment number of called lines next in process and the address of the register buffer in service, to store the equipment numbers of called lines in process, to store the various items of information for transfer between processors, and to store the buffer address of the register, auxiliary register, or supervisory in service for a connection and subject of a processor-tester-marker-driver transaction. Each processor also has tables to discriminate two digit prefixes, to obtain directory to equipment number translations, and to establish class of service. Programme structure.-An inter-processor output interrupt programme controls transmission between the inter-processor communication hopper and the inter-processor register in the direction of the other processor. An interprocessor input interrupt programme controls the corresponding transmission in the other direction. A clock interrupt programme is initiated every 14 ms. to compare present with previous states of lines at line circuits and on both sides of junctors and to inspect the next-in-process called line hopper. One eleventh of the total scan is undertaken at each clock interrupt so that one complete scan is made each 154 ms. The clock interrupts in one processor start mid-way between the clock interrupts in the other processor so that the work taken up by each processor is kept separate. A tester-marker-driver interrupt programme controls the dialogue between the tester-marker-driver hopper in the processor and the tester-marker-driver circuits. The base level programme comprises the residue of deferable operations such as high speed scanning of register, auxiliary register, and supervisory buffers and originating call hopper, at 154 ms. intervals. The register buffers may also be scanned at 15 sec. intervals and the supervision buffers at 2 min. intervals. Examination of test points and of the other processor fault bi-stable is carried out by a maintenance sub-programme at base level.