Patent GB-937907-A (GB)
Title: Telephone switching systems
IPC: H04Q3/545
Filed: 1960-11-23
Abstract: 937,907. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Nov. 23, 1960 [Nov. 25, 1959], No. 40274/60. Class 40 (4). In a switching system in which the operation of the switches is controlled by a control circuit which includes a temporary memory having a plurality of devices for storing information of at least two levels of importance, which devices when in normal operation are associated in pairs with each member of a pair containing the same information, means is provided for detecting a failure of one of the devices and for generating a failure signal, in response to which the information of lesser importance is erased from another storage device and the information of greater importance stored in the one device is inserted in the other. The embodiment described consists in a modification of the system disclosed in Specification 904,164, which system includes inter alia a temporary memory in the form of a barrier grid store which stores two classes of information. The first relates to the state of subscribers' lines and the progress of current calls, and the second consists of system administration information such as current directory number to equipment number translations Detailed description.-In Specification 904,164 only one barrier grid store tube is employed, whereas in the present system four such tubes, BGS-A to BGS-D (Fig. 4), are employed, additional programme words to define the particular tube to be used, and additional sequences to pin point faults in the tubes and to rearrange the information therein being included in the system programme. A single line in the drawings in many cases represents more than one conductor and will be referred to as a pair or as a conductor group as the case may be. It is assumed that the system is operating in the no-trouble mode; that the alarm flip-flops (bi-stable circuits) 6006, 6007 are in the " 0 " state, the trouble flip-flops 6001-6005 in the trunk signalling selector are in the " 0 " state, the trouble relays 5024-5027 are down and that the restore flip-flop 6010 is in the " 0 " state. BGS-A and BGS-B are then in use asregular stores for the "A" and " B " groups of lines and BGS-C and BGS-D as their respective standbys. Assuming that call progress information relating to the "A" group of lines is requested by the common control 110, an order will be placed on the translation cable 406 which, in combination with a pulse on the execute present order lines EPO, will enable AND gate 5021 and set the TBO flip-flop 5013. Boolean equations governing the functioning of the input control translator 3006 and the output control translator 4020 are included in the Specification and in accordance with these the present order results in the energization of conductors G1 (3007) and G3 (3009). The appropriate read and regenerate (3010), read and write " 1 " (3011), read and write " 0 " (3012) and read and change (3013) gates are energized from the BGS read-write control 1107 (Fig. 5) in accordance with orders from the permanent store 111 (Fig. 5). Identical information should then appear at the output conductors 4005 and 4007 of the BGS-A and BGS-C tubes. The output control translator energizes conducts H1 (4027) and J3 (4014). The output of the BGS-A tube is thus gated from pair 4005 via AND gate 4021 and OR gate 4025 to the right side of both the A match circuit 4011 and the B match circuit 4012 and to the BGR flip-flop 735, and that of the BGS-C from pair 4007 via AND gate 4009 to the left side of the A match circuit 4011. If the signals applied to the right and left sides of a match circuit are identical or if the input conductors on one side are not energized, no mismatch signal is given. If, however, the signals applied to two sides differ, the circuit concerned gives a mismatch signal which sets the relevant one of the alarm flip-flops 6006, 6007. The points 6008 and 6009 are included in the points scanned by the line and trunk scanner 108 (Fig. 6) and as soon as one of the alarm flip-flops is found to be in the " 1 " state, a trouble locating sequence is undertaken. Each of the tubes associated with the mismatch is tested (a) by checking the address registers, (b) by checking the tube's ability to execute required commands at a desired address, and (c) a read-around test in which " 1 " or " 0 " is written in a test area, reading and writing is repeatedly performed in nearby storage spots and the original test area is then read to see if it still indicates the state originally written therein. Any barrier grid store fault present will be found by these tests. As soon as the faulty tube has been identified the common control causes trunk signalling selector 118 (Fig. 6) to set the corresponding flip-flop of 6001-6005 say 6002 corresponding to tube A, and the A trouble relay 5024 is energized. This lights the lamp 5028 and marks the conductor 5001 leading to the input control translator 3006. Common control then introduces a programme which point by point reads the storage areas of tube C carrying the administration information relating to the A group of lines and writes it into that part of the D tube which normally contains the line and register information relating to the B group. In this way the administration information is retained in duplicate in the single trouble mode of operation. If a second tube fails, no duplicate records can be kept and in the double trouble mode all the information is stored on the two remaining tubes, one tube per group of lines. When the fault on a tube has been cleared, the restore flip-flop 6010 is set, either manually by key 6013 or automatically by flip-flop 6001. When next the point 6011 is scanned in the main programme it will be found in the " 1 " state, and a series of programme steps is undertaken to restore the system from the double trouble to the single trouble mode, or from the single trouble to the no trouble mode, as the case may be, the restore flip-flop 6010 being then automatically reset by means not shown.