Patent GB-1123282-A (GB)
Title: Improvements in or relating to communication systems
IPC: H04Q11/04
Filed: 1965-11-25
Abstract: 1,123,282. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. 25 Nov., 1965 [27 Nov., 1964], No. 50133/65. Heading H4K. In the system of PBX's described in Specifications 1,029,204, 1,045,521, in which each PBX is a t.d.m system and all PBX's are controlled from a common programmed centre at the central office, the common control is provided with a maintenance program. Processing in the common control proceeds over sectors devoted to each PBX, the routine for each PBX including a test routine for equipment at the PBX; when all these sectors have been cycled a test routine is taken up for the common control equipment. The system uses duplicate equipment worked on-line and off-line according to a set switching plan or when off-line equipment is substituted for on-line equipment in fault conditions. The switching unit at each PBX duplicates the t.d.m. highway, line scanner, transmitters and receivers, data circuits and network control circuit. The common control duplicates the transmit and receive data circuits in its input-output section and duplicates its program control circuit, program store, and call store, to provide an alternative processing unit. The data channels between common control and the PBX's are also duplicated. In its cycling of the associated call store a program controller comes across a maintenance instruction and obtains from the associated program store commands which it passes to a translator in the maintenance centre. One such translator is provided for each program controller and a translator is on-line or off-line along with its associated controller. The maintenance centre determines the working configurations of the input-output section of the control centre, the PBX's and data links, and determines which processing unit is active. Timers automatically indicate a fault if a test response is not in evidence within 2 sees., and effect transfer of control to the stand-by processor. A 20 minute timer effects such transfer during fault free periods. A control panel has a lamp display to indicate trouble conditions and the content of various registers. Alarms are provided and are classed as minor or major. Test call routines can be undertaken as a check on PBX switch units and central control digit receivers. Tests can be directed towards selected points in the central control. Comparison of the entire contents of the program stores is also made at 2 second intervals, a mismatch halting the comparison and preserving the off-line store data for analysis. The on-line processor unit is subjected to a series of tests spread over as many as 256 exchange system cycles. If a trouble condition is encountered the maintenance centre prepares to transfer control to the off-line processor but will in general do so only after a repeat of the on-line tests gives confirmation of the trouble. Off-line tests are conducted by interrogation of the off-line program store by the on-line control unit and differ from on-line tests in that they are diagnostic and print out messages giving the locations for the troubles that arise. On-line call store data is duplicated in the off-line call store and the sets of data may in certain circumstances be exchanged. Other tests of trunks, data transmission, and PBX switch units, result in substitution routines when a fault is discovered. The last piece of duplicate equipment removed by substitution before a fault free configuration is achieved being classed as faulty. Where all configurations fail to cure the fault a trouble report is printed out and further maintenance routines are suspended in that particular respect.