Patent GB-1120651-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
Inventor: LAWRENCE JOHN ALBERT
IPC: H04Q3/00
Filed: 1964-07-31
Abstract: 1,120,651. Automatic exchange systems. H.M. POSTMASTER GENERAL. 30 July, 1965 [31 July, 1964], No. 30349/64. Heading H4K. In an exchange system utilizing matrices of reed relays in the speech path, selection of a path proceeds in a step-by-step manner. The switching network includes a plurality of stages, each of which has at least one register and control circuit uniquely associated therewith. Each stage comprises a plurality of groups of switches and each group is composed of first rank reed matrices that are preferably linked to second rank matrices so that full availability exists between inlets to the first rank and outlets from the second rank. A discussion on, the blocking of, linking between first and second ranks of, and grading in, such switching stages is given in the Specification. General description. Fig. 5.-Incoming lines are connected to one or more inlets on eight first rank (A) switches of a group. Each switch is a 12x20 cross-point matrix whose 20 outlets are evenly distributed over the inlets to 20 B switches. Each of the latter switches, B1 for example in Fig. 5, is an 8 x 10 matrix whose 10 outlets correspond to the first choice outlets for each of the ten different routes 1 to 0, and similarly the outlets of switch B20 represent the last choice outlets for these routes. In operation of a stage, a call isolator selects one of a possible plurality of calling lines and connects its register access unit (junctor) via a register access switch to a register where an incoming digit is stored. The digit indicates which of the routes 1 to 0 is required. When the control circuit becomes free it selects a path from the calling inlet to the required outlet, switches through the connection and then releases the common apparatus. In addition to the normal a, b and c (or S) wires, the intrastage connection includes an H (hold and energization) lead. More detailed description, Fig. 6.-The call isolator selects one of the calling lines on a variable priority basis, connects the chosen line to a register and marks the inlet of the A matrix to which the line is connected and the inlets of the B matrices to which the A matrix has access. The availability of the AB links is determined from the potential on the S leads of the links and is compared with the availability of outlets in the route denoted by the digit received in the register. The result of the comparison denotes an available B matrix and if there is more than one, a variable priority selection is again made. The selected outlet in the required route is then marked so as to bring-up and hold, over the H wires, the relevant cross-point relays. Faults in the sequence of operations or delay in releasing the equipment operates alarms and force-releases the connection. Particular description.-In the following, numerous references to Figures of the drawings are given but these Figures are not shown herewith. A calling circuit applies earth to the S lead (Fig. 11), whereby LR comes up to mark a start lead 13 which is commoned with the other eleven inlets of this A matrix to a lead 23 (Fig. 12). Each of leads 23 thus pertains to a particular A matrix and extends to its own inlet 41-48 (Figs. 25-28) of a call isolator. If more than one line is calling the isolator selects one of them on a priority basis utilizing a transistor chain 416-428. A bi-stable circuit (transistors 410-413) controls the operation of relays PA and PB, the former causing selection to take priority in the direction 41 to 48 and the latter in the direction 48 to 41. After each call is completed a pulse on terminal 414 triggers the circuit so that the two directions have priority alternately. If neither or both relays PA and PB are operated, transistor chain 434-436 (Fig. 29) is energized to bring-up slow-to-operate relay AL which controls an alarm circuit. The selection is denoted by operation of one of relays A to G which, inter alia, mark a lead such as 431 (Fig. 29). The mark is extended over leads 24 (Fig. 12), 11 (Fig. 11) and wire 15 to another inlet such as 31 (Fig. 13) of the call isolating circuit. Inlet 31 is common to the first level of each of the eight A switches and similarly inlets 32 to 312 are common to the other levels. The previous 1 out of 8 selection (Figs. 25-28) effectively selected one of the calling A switches, whereafter the selector of Figs. 13-22 operates in an analogous way to select 1 out of the 12 calling inlets of the selected A switch. The 1 out of 12 selector's bi-stable circuit (Fig. 24) is triggered over lead 433 (Fig. 29) whenever the 1 out of 8 selector operates and an alarm is given if neither or both priority relays PPA and PPB are operative. Thus considering the first inlet of the first A switch, relays A (Fig. 25) and J (Fig. 16) are now both up and these cause energization of a cross-point coil XA1 (Fig. 12) of a register connector whereby the chosen calling line is switched through to a register (Fig. 32). The calling earth on the S wire thus brings-up relay BB (Fig. 34) which causes a + 12 v(s) proceed-to-send signal to be returned over both the a (+) and b (-) wires, the relays A and J in the call isolator to be held and relay CP to operate. An incoming digit in the form of 1 out of 4 potentials on the a and b wires are detected by the circuits of Figs. 30, 31 and 33, 34 respectively. Transistors 511 to 514 respond to different values of signalling potential and switch-on their associated transistors 520-523. The highest-numbered operated one of the latter inhibits lower numbered ones via a diode matrix 524 &c. and brings up its associated relay RA-RD. Similarly, one of relays RY to RW operates, whereby a marking is extended over one out of 10 leads 534-543 (Fig. 35) and relay SR comes up to revert a digit-received earth signal on the a, b wires. Assuming the digit received is 1, lead 81 (Fig. 42) is marked whereby, in the link interrogator (Figs. 38-42), transistor 811 followed by relay MKJ1 operates. Consequently, those of relays TK1-TK20 (which are multipled through diodes 832 &c. to each of the S outlets of the corresponding B switches), which are not shunted by earth (busy) on the S wires, come up. A release signal is thereby applied to terminal 559 (Fig. 35) so as to cause SR to drop and thus release the register and remove the earth from the a, b wires. In order to select a free AB link the 1 out of 8 selector mentioned above causes an earth marking to appear on lead 834 (Fig. 42) (this corresponding to switch A1 and transistor 842 followed by relay MKA operates. Consequently, in a similar manner to the operation of the TK relays, one or more of relays LK operate to indicate free outgoing links from switch A1. Since only some of the B switches accessible to these free links will be available for the required connection to be set up, the contacts of LK are inserted in series with those of TK c.f. Figs. 40 and 41, whereby further selection requires the simultaneous operation of an LK and a correspondingly numbered TK relay. The selection proceeds on a 1 out of 5 basis (Figs. 46, 47) followed on a 1 out of 4 basis (Figs. 43, 44), whereby eventually one of relays SA-SE and one of ST-SM is operative to denote the selected link. The 1 out of 4 selector includes a priority bi-stable circuit and an alarm circuit similar to that described above. Contacts of the operated relays from each selection complete a chain (Fig. 50) so as to cause operation of a particular cross-point and thereafter to hold the crosspoint (relay K, Fig. 11) and to release the control circuits (relays RLA, RLB, Figs. 36, 38). If release does not occur within 200 msecs. of operation of a J-U relay, forced release by relays FAL and FR (Figs. 36, 37) occur and an alarm is given.