Patent GB-1189645-A (GB)
Title: Improvements in or relating to Telecommunications Switching Systems.
Inventor: LEAKEY DAVID MARTIN
IPC: H04Q3/00
Filed: 1966-03-28
Abstract: 1,189,645. Automatic exchange systems. GENERAL ELECTRIC and ENGLISH ELECTRIC COMPANIES Ltd. 24 May, 1967 [28 March, 1966], No. 13497/66. Heading H4K. In an exchange having a plurality of group selector units whose corresponding outlets are multipled and connected directly or indirectly via auxiliary selector units to a greater plurality of final selector units, each group and auxiliary selector has its own register/translation field which is supplied with two digits during the setting-up of a connection, these same two digits being repeated from the group to the auxiliary selector's register in the event that the connection must be set-up indirectly. Some of the final selectors can only be reached via the auxiliary selectors. It is suggested, although not described, that the auxiliary selectors may be used as an overflow route in the event that direct routes are busy. It is also suggested that the final selectors may in fact be second group selectors having access to outgoing junctions Trunking (Fig. 1, not shown).-Each of the group selector units (1A to IF) and the auxiliary selector units (1G, 1H) comprises two or more stages of read-relay matrices having 96 inlets (L3) and 200 outlets, the latter being grouped into 10 levels (L4) of 20 paths each. Corresponding paths in corresponding levels from each selector are multipled. Each of the final selectors (2A-2M) has a maximum of 45 inlets and 1000 outlets, the actual numbers being determined by traffic loading. The final selectors (2A, 2C-2I) are each connected directly to particular levels from the group selector while the final selectors (2B, 2J-2M) are each connected directly to particular levels from the auxiliary selector and hence indirectly to one or two levels from the group selector. Each group selector contains a translation field for determining, from the 2 incoming digits, in which of its levels a free path should be selected. Similarly each final selector contains a translation field for determining, from the three incoming digits, which one of its outlets is required. Each subscriber is identified by a 4-digit directory number (c.f. the numbers in the final selector boxes) the first two digits being used by the group selector and if necessary the auxiliary selector and the last three digits by the final selector during the process of setting up a call. Selector units (Fig. 12, not shown).-Each 4- wire inlet (a, b and 2 control/supervisory) to a selector unit has an individual supervisory circuit (102) which is connected to the units register/translation field (103) under the control of an allotter (104). The supervisory circuit is described with ref. to Fig. 13 (not shown) and contains, in addition to the usual relays, a Zener diode/resistance network which is connectible to the a, b wires for transmitting backwardly a signal indicating the nature of the unit (see below). When the unit's register has received the necessary 2 or 3 digits it controls, in a manner not specified, the operation of the appropriate crosspoints in relay matrix (101). Setting-up a call.-Looping of a subscriber's line 6A, 6B (Fig. 2, not shown) causes a contact 7 to close in his allotted register access circuit 3 (R/A circuit) whereby a free register 4 is seized and its individual relay RA in the R/A circuit is operated. In the register (Figs. 3-8), a relay RC, which is down in each free register, comes up whereby a register allotter 15 (Fig. 2) is seized over wire 14 in order to select one of the registers by a marking on wire 16. The operation of RA brings up GS, A and RCC. Relay RC falls back followed by RCC (when the reg. allotter releases) and RCB then comes up followed by RCA. Dialled digits are repeated by A to a 4-stage binary counter 22 and a temporary relay store DA-DD. Each intertrain pause is detected by circuit 23 which clears the counter and causes the stored digit to be " permanently " stored in a binary relay store 27 (Fig. 4). The latter comprises 4 stages (denoted by relay contacts KA-KD) successive digits being directed to successive stages by a digit distributer (bottom of Fig. 4). Another, transistorized digit distributer 31 (bottom of Fig. 5) " reads-out " the stored digits after two have been received-as denoted by the operation of relays ASR, HH, DR, SH and HHA (Fig. 5) in order to seize a common sender (Figs. 9, 10) over leads 57-48 (Fig. 7, relays RSA, RSB operative). The operation of HH and HHA applies a starting earth to lead 50 (Fig. 2) which is connected (via R/A circuit 3) to an individual 1st group selector unit (G/SU). In addition SA in the R/A circuit is brought up in order to connect the sender (Fig. 2) to the a, b and control (61) wires leading to the group selector. The latter reverts a proceed-to-send signal (+12 V on a and b wires) which is used by the sender for extracting the first stored digit from the register. The sender causes SN (Fig. 7) to come up whereby normally operative ODP falls back and the first output digit-distributing- relay XA1 is energized. The stored digit as indicated by the operated combination of contacts 1SA2-1SD2 is thus passed in binary form over leads 72 to the sender. In the latter, a code converter (relays Y, AA, WA) translates the binary coded digit into a 1 out of 4 and a 1 out of 3 code. A pair of Zener diode chains are then used for transmitting the latter code in multipotential form over the a, b wires 60A, 60B (Fig. 2). The G/SU responds by reverting earth on the b wire. The sender informs the register accordingly whereby the second digitdistribution-relay XB is brought up in order to convey the second digit to the sender and hence to the G/SU when the latter reverts a " proceedto-send " signal. If the G/SU connects through to an auxiliary G/SU either because of the grading or for reasons of overload, the auxiliary G/SU reverts an identification signal which is recognized in the sender as a command to retransmit the first two digits. (This is accomplished in the register by the operation of RGS (Fig. 7)). When connection to the individual register/translation field of the appropriate final selector unit is established, another identification signal is reverted to the sender which thereupon brings up FSB in the register so that the last three digits can be sent forward (operation in succession of distributed relays XB, XC, XD). Register/translation field (Figs. 15, 16).- After a supervisory circuit has been connected to its selector unit's register/translation field, a relay BA (Fig. 15), followed by BAB and DRA, comes up so as to connect two transistorized voltage level detectors 114, 115 (Fig. 18, not shown) via leads 113, 112 to the incoming a, b wires. Relays BAC, SCA, SCB and PS follow in succession, PS being effective to revert a proteed-to-send signal. The subsequently received digit is analysed by the detectors 114, 115 and one each of the two sets of wires 116-119 and 121-123 is marked. Consequently one each of CW-CZ and FA-FC (not all shown) come up followed slowly by HC. A relay in the matrix MA-MJ (Fig. 16) corresponding to the digit is thus energized. When HC does operate, it releases SCA, SCB and brings up AC. The latter releases HC and reverts an " acknowledge " signal. In response thereto, the sender removes the multipotential signals from the a, b wires so that the holding potential for AC is removed from leads 127. Relays SDA and SDB come up in order to initiate transmission of the second digit which is finally stored on one of the relays in matrix NA-NJ. HD follows slowly and acts in a similar manner to HC. Since the contacts of the two relay matrices are connected in tree formation (only MB1 and NG1 are shown at the top of Fig. 16), one of the selector's outlets is now effectively marked. The appropriate crosspoints are operated to connect this outlet to the inlet supervisory unit.