Patent GB-1029074-A (GB)
Title: Telecommunication exchange apparatus
Inventor: HOULDSWORTH JACK
IPC: H04Q11/04
Filed: 1963-08-27
Abstract: 1,029,074. Automatic exchange systems. ERICSSON TELEPHONES Ltd. Nov. 25, 1964 [Aug. 27, 1963], No. 33816/63. Heading H4K. In a register impulse trains representing digits are recorded in serial binary form in regenerative stores access to which is governed by a cycle of group pulses each of a duration equal to a time frame in a time division multiplex, the bits recorded in the regenerative stores being read out in time slots of the multiplex and being processed in an adding circuit the carry output from which is delayed by one time slot. Pulses.-Each time slot p has a duration of 3À4 Ásec. and there are 30 slots to a multiplex time frame. A cycle of 56 group pulses g, each of a duration equal to a time frame and occurring in coincidence with the frames, is employed together with a cycle of 13 vernier pulses v of the same duration. A cycle of 30 sharing pulses s, each equal in duration to a vernier pulse cycle is also used. Pulses bal and ba2 which alternate, and pulses bb and bc occurring in cycles of 7 and 3 are also provided. The exchange system employs a number of registers identified by combinations of the bb and bc pulses. When a register is seized a test is made to ensure that a free path exists for the calling subscriberregister connection. If no path is free the register releases itself. Reception and storage of dialled digits.-The  register comprises five delay line circulating stores ST1-ST5 each having a capacity of 30 serial bits in the time slots p1 to p30 and a circulating time equal to the multiplex time frame. The presence of a dial break is signalled to the register which records the condition on a bi-stable circuit providing an output BK. With BK present a count is commenced in ST5 with an addition made in each of the group pulses g24 and g52. When a carry output appears from the adder circuit in time slot p4 the BK output has survived for 22 ms. and a bi-stable circuit is set to give output MBK indicating that a minimum acceptable duration has been detected. Outputs BK and MBK erase the bits registered in slots p1 to p18 of store ST1 which is employed in supervizing dial tone as described later. The timing of the BK output continues in ST5. When the break impulse ends, a bi-stable circuit gives an output MK which in conjunction with MBK starts up a count from slot p4 in ST1 which is accessed in group pulses g51. After a count of two group pulse cycles (an interval of 11 ms.) a bi-stable circuit is set to give output MMK for the minimum acceptable make period and its existence with MK signals the detection of a valid impulse. Each recorded decimal digit is accommodated in a block of 6 time slots in the stores ST2-ST4 which have a maximum capacity of 15 dialled digits. The first slot of each block is provided with a digit, termed the distributer digit, to indicate that that block is active in having a number registered or being read out. The last slot of each block provides space for an overflow digit. A distributer digit being in readiness in slot p1 heading the first block in store ST2 access in group pulse g54, the appearance MK and MMK for each impulse of the first impulse train effects an addition to the binary count in slots p2-p5. For each addition to output MK is removed. The duration of the output MK showing the make condition from the end of a break pulse is continued to be counted off in store ST1 beyond the count of 2 which gives rise to MMK so that, should a counter carry output appear in time slot p6 after a duration of 95 ms., a bi-stable circuit is set to signal an inter-train pause with its output ITP. Given ITP with MK the distributer digit is erased from the head of the first storage block and written into slot p7 at the head of the next block to attract registration of the next digit. The digits in p2-p5 of the first block are converted into their complement. Transient pulses.-If a break impulse disappears before a minimum duration is signalled by MBK a checking count is undertaken in ST1 from slot p1 so that if the interruption persists for longer than 5 ms. the BK output is removed and the count timing its presence in ST1 is erased. If the interruption does not endure as long, the BK count continues and as soon as MBK signals its sufficient duration the checking circuit is released. Sending digits.-This is done on instruction from a marker when an outgoing junction path has been set up. If the junction terminates on a selector the store ST1 counts out a delay of 575 ms. in slots p20 to p24 to allow terminal equipment to be seized before digits are sent. If the junction terminates on a register in a switching centre the delay is reduced to 315 ms. The digits, registered in complementary form, are counted out in step with transmitted impulses, the distributer digit at the head of each register block being stepped from block to block as the digits are sent. Store ST1 in slots p19 to p24 counts out inter-train pauses of 850 ms. or 310 ms. depending on whether the pulses are sent to a selector or a register. The store ST1 also acts as a counter to measure off the make and break periods of the impulses. A period of 4 seconds is measured off by ST1 after the last digit has been sent, during this period the calling subscriber is connected forward to hear call progress tones and at the completion of the period the register is cleared and released. Register release and call observation.-If the BK output coincides with the open loop conditions for over 180 ms. the register is cleared down and released. The register can, however, be held for any length of time from an observor's position at which a slave register presents the main register operation for inspection. Association of Register with marker.-The register has access to a marker during a coincidence of ba, bb and bc pulses. The register is instructed by the marker when it is necessary to connect number unobtainable, busy, and equipment engage tones, or to send impulses over a junction. The marker also interprets the register store digits to cause the register to signal appropriately when metering for an STD junction call is required, when a subscriber sets up a standing instruction for the diversion of incoming calls or cancels such an instruction, when an operator sets up a standing instruction which bars incoming calls to an indicated subscriber or when such an instruction is cancelled, when an emergency call is being set up and a call trace procedure is to be followed, and when the Y party to a shared line is the calling or called party. The dialled digits accumulated in the delay line circulating stores of the register are read out in their complementary binary form to operate bi-stable circuits which provide the inputs to a binary to decimal converter. The digits are read out from the storage blocks to a maximum of four digits at any one time, the presence of a distributer pulse at the head of a storage block inhibiting read out as the block is still in receipt of impulses. The binary to decimal conversion introduces a discrimination between STD calls from ordinary subscribers and such calls from coin boxes, the digit 0 from ordinary subscribers remaining unchanged but becoming 00 in the conversion for coin boxes, thus enabling the calls to be routed over different outgoing junction groups. Register identifies Y party of shared line.-At the end of each impulse train dialled by a Y party a short extra impulse is sent which is between 0À36 and 0À73 of a normal impulse. Two counting procedures are set up in store ST5, one count at 2À8 ms. intervals being conducted in slots p1 to p7 and a second count being conducted at 1À4 ms. intervals in slots p8 to p14. Whenever an impulse is detected with its consequent production of signals MMK and MK, the two counts of the impulse in ST5 are complemented and the counts in p1 to p14 are stepped down to p1 to p28 so as to clear the counters for the next impulse and preserve a record of the last impulse. The next impulse controls the count so as to register its duration in p1 to p14 as before, and also to count out the complementary record of the previous pulse in p15 to p28. The different rates of counting are such that if a carry output appears in slot p21 the impulse exceeds 0À36 of the previous pulse and if a carry output appears in slot p29 it exceeds 0À73 of the previous impulse. The presence of a first carry and the absence of the second carry signals the presence of a Y party identifying impulse and prevents its registration as part of the impulse train proper. The Y party is not fully identified until two such identifications have been made. Register delays connection of dial tone.- The exchange system is such as to give rise to parked subscribers, which are subscribers who have held one end of a connection the far end of which has been discarded and for which supervision has been forcibly relinquished. Dialling from such a subscriber will effect seizure with its first impulse which is likely to be lost. Dial tone is consequently held off the line until a count has been made from slot p7 of ST1 to reach p9. Any impulses received during this period are presumed to be from a parked subscriber and are answered by the connection of NU tone. Dilatory dialling.-A call is timed out to NU tone if no dialling impulses have been received within 30 seconds, timing being done in slots p13 to p18 of ST1. Classes of service.-A register determines class in the v5 pulse position in coincidence with a characteristic s pulse. Before dialling takes place the register is' acquainted with trunks barred condition for ordinary subscribers, coin collecting box calls, and a call diversion procedure by a subscriber. As a result of dialling the register determines disabled subscribers, and outgoing calls and trunks barred separately for X and Y parties to a shared line. Selected subscribers may have the trunks barred condition removed in response to a low p