Patent GB-1239973-A (GB)
Title: Improvements in semi-electronic tele-communications systems
IPC: H04Q11/04
Filed: 1968-07-01
Abstract: 1,239,973. Automatic exchange systems. CSELT CENTRO STUDI E. LABORATORI TELECOMUNICAZIONI S.p.A. 1 July, 1968 [4 July, 1967; 29 April, 1968], No. 31245/68 Heading H4K. A satellite exchange system comprises an electro-mechanical switching matrix at the satellite exchange and a corresponding matrix at the main exchange, corresponding columns of each matrix being connected by a group of satellite links and the matrices being served by time-division-multiplex control circuits which define a primary cycle of time slots for each row of the matrices, the primary cycles being employed alternately to receive from and transmit over a data link between the main exchange and the satellite. A satellite UR, Fig. 4, has 50 subscribers U connectible over a relay matrix MDS<SP>1</SP> to 9 exchange links g under control of a circuit CDTCC<SP>1</SP>, a corresponding circuit UC at the main exchange terminating the 9 links g on a relay matrix MDS controlled by a circuit CDTCC. Calling conditions from satellite subscribers are signalled on leads C<SP>1</SP>1-C<SP>1</SP>50 at the satellite while connections to the satellite subscribers are set up in response to signals on leads C1-C50 at the main exchange. A data link 18, terminated on receiver/transmitters, is provided between the satellite and the main exchange. The control system works on a repetitive multiplex frame of ten cycles dg, nine of the cycles dg1- dg9 being used to supervise respective ones of the links g1-g9 in turn, the tenth cycle being used for unspecified control functions. Each of the nine link cycles dg is divided into two identical sets of 64 time slots, the first 14 of each set being used for synchronization and control while the remaining 50 time slots du1-du50 of each set are permanently allotted to satellite subscribers. The first set e of time slots is used to scan for calling conditions at the main exchange while at the satellite the first set is used to identify a calling condition found at the main exchange and signalled over data link 1s. A link is identified by the link cycle and a subscriber by the time slot in which a signal is sent. The second set d of time slots in each link cycle is used conversely to scan for calling conditions originated at the satellite and to identify the calling subscriber as signalled over data link 18 to the main exchange. Data link 1s is, therefore, used for transmission in one direction in the first set of time slots and in the reverse direction in the second set of time slots in the supervision cycle of each link. As shown in Fig. 6 the multiplex frame is defined by three cascade ring counters CP, CC, CS, of 64, 2, and 10 steps, respectively. CP defines the subscriber time slots du and defines control pulses of which only ds and ds<SP>11</SP> are shown and considered. CC switches the control circuit between the receive and transmit modes relative to the data link 1s by defining the first and second sets of time slots e and d. CS defines the link cycles dg and control cycle dgs. Fig. 6 shows the main exchange relay matrix and associated control circuit, the satellite being similarly provided. A connection is set up in the matrix by driving a row amplifier AMR corresponding to a subscriber and a column amplifier AMC corresponding to a free link dg. A connection once made is held by a circuit T of a column. In its cycle of the multiplex each link is available over a gate 4 unless it is busy in which case the gate 4 is inhibited by hold circuit T. At the start of each cycle of CP a pulse ds over gate 14 is applied to the gates 4 so that if the link, the cycle of which is currently in force, is free, the pulse is propagated over gates 6, 7 and 9 to set a bi-stable in availability circuit CD provided that gate 9 also receives a pulse over that data link 1s to indicate that the link is also free at the satellite. With the bi-stable set gates 12 and 13 are primed so that in the first set of time slots dul-du50 defined by output e of counter CC, the leads C1-C50 are scanned over gates 1 to look for calling conditions originating in the main exchange. A calling condition results in a pulse in the time slot of the wanted satellite subscriber and on the row of that subscriber's appearance on the matrix MDS. Over gates 14 and 4 the column is also driven to make the connection in the matrix to the link marked out for supervision by the dg pulse. Over gates 14, 8 and 10 the pulse is sent to the satellite to identify the subscriber so that a corresponding connection can be made to the link at the satellite. Over gates 14 and 8 the pulse resets the bi-stable in CD to disconnect further scanning on gates 1. With the bi-stable in CD set in respect of a free link and the second set of time slots du1-du50 defined by output d of CC, gate 12 is open to pass pulses received from the satellite over data link 1s. As with the main exchange in the first set, the satellite at this time is scanning leads C<SP>1</SP>1-C<SP>1</SP>50 for calling conditions originated at the satellite, a calling condition resulting in a pulse to the main exchange where it coincides with the time slot of the calling subscriber and over a gate 2 drives the corresponding row and the column of the link being supervised to effect connection over MDS corresponding to that set up in the satellite. The bi-stable in CD is also reset to busy the link. Release.-Release is effected at the main exchange in response to disconnect signals d1-d9 appearing on links and timed for persistence in a circuit SDG. As shown in Fig. 7, a release signal d in a link cycle finds a path over gates 21, 22, 23, 26 and 28 to drive a counter or integrator FR, three or four counts being required before a release signal cd is sent to unlock the appropriate hold circuit T. As soon as a release pulse d is detected a one-shot multivibrator R blocks the input to FR for a period of one multiplex frame so that only one release condition is handled at a time. A release signal rt is sent to the satellite to start a corresponding release process there. Fault conditions.-If as a result of noise or malfunction the availability of a link as signalled on lead pc at the main exchange disagrees with the availability of the link as signalled on lead pr from the satellite, gate 24 or 25 providing a simulated release signal, FR times the condition and effects release.