Patent GB-1125563-A (GB)
Title: Improvements in or relating to automatic switching systems
Inventor: PAGE PETER COLIN
IPC: H04Q3/54
Filed: 1964-11-09
Abstract: 1,125,563. Automatic exchange systems. GENERAL ELECTRIC CO. Ltd. 5 Nov., 1965 [9 Nov., 1964], No. 45540/64. Heading H4K. In a system having a plurality of common equipments which are taken into use sequentially for successive calls, each equipment normally serves a predetermined number of consecutive calls but is immediately released and the next one seized if a fault is detected during its period of operation. As described there are two common control circuits each of which normally serves eight calls before switching over to its partner, but, in the event of a fault occurring, the current one is immediately locked-out and the partner takes over completely until the fault is cleared. The following faults, which are described in more detail below, may occur:-more or less than a specified number of relays operate; time-out circuits operate before their corresponding functions are completed; wrong relay operates; and correct relay fails to operate. In the following, certain Figures are not showndenoted by F.7 for example which means Fig. 7. not shown-although components therein are referred to by number for ease of description. General description.-The system comprises a 1000 line exchange in which the line circuits 5 (Fig. 1) are scanned, for connection one-at-a time via a three stage read relay network to an outgoing relay set 10, 11 or if these are busy to a local relay set 9. Dialling tone is reverted and incoming digits are registered. If a local call is required, the original path to relay set 10, 11 is dropped and a new one to set 9 is established during the interdigital pause following the exchange code. The common control circuits 17 each normally operate alternately for a predetermined number of calls. Switches.-Each A, B or C switch is a degenerate 13 x 13 reed relay matrix in which an input path has access to four output paths only. Each crosspoint consists of + ; -; and P-wires; a holding wire which includes the relay coil and a series connected normally open contact; and a marking wire connected through a rectifier to the junction of the coil and its contact. Trunking.-The A switches are divided into groups with the outlets of each of the up to 4 switches in a group commoned and taken to respective B switches. The latter are divided into 10 groups, again with outlet multipling for the 4 switches within a group, and connected via B links to one switch in each of 4 C groups, there being 6 C groups altogether. Through a 4 C group, access can be obtained to two local and two outgoing relay sets. General equipment.-Each A, B or C group has an associate reed-relay connector e.g. 48 for connecting the 13 private wires of each group to an A, B or C link selector e.g. 14 respectively and, in the A groups only, for connecting the wires to an A-link marker 56. A calling line is identified by a magnetic core translator 129, which is connected to a free register 108 by an allotter 123. The register seizes a common marker 93 and supplies the identity of the caller to reed relay matrices therein whereby a marking is applied over one of 13 wires 94 connected to the A link selector. Since the A-switches are identical, only thirteen wires are required for this purpose, the identity of the switch being found as will hereinafter be described. Each link selector is similar and consists essentially (Fig. 13, 14) of 13 inputs (e.g. wires 94) each connected via a jumper field to 4 (out of 52) AND gates. The other inputs of all these AND gates are connected to a counting circuit 199 controlled by common control. The gates are divided into groups of 4 (the gates of any one input all being in different groups) and each group's common output is connected to a further AND gate whose other input is fed with free/busy information via wires 53 (Fig. 1). These last AND gates are respectively connected to reed relays A-N . In the operative control circuit 17 (F.7-12) a relay C is up so as to connect the circuit 17 to the system. Fault detectors (F. 9, 10) which include inter alia timing circuits, manual and automatic lock-out relays and a counter for counting the predetermined number e.g. 8 of consecutive operations of the current control circuit are cross-connected to similar detectors in the other control circuit (not shown) whereby only one control is operative at a time and the alternative one is taken into use for completing a connection immediately a fault is detected in the current one. A fault evaluating equipment (F. 16, 17) is triggered by each negative pulse applied to leads 385 from the fault detectors so as to step a pair of control cams. If steady negative battery, due to a full fault condition, is applied by one control circuit, the switch selfsteps whereby the two pairs of cams get sufficiently out-of-step fro a lock-out relay to come up. This relay actuates an alarm and energizes lock-out relay LO (in Fig. 9). LO may, alternatively, be energized manually. In either case, this control circuit is taken out of use until the fault has been rectified and LO released. The fault evaluater is disconnected during this time. In addition if a steady negative potential does occur, it is applied to a clock pulse generator and various bistable circuits in the control circuit so as to inhibit these and is also used to clear the bistable circuits in the linkselectors so that the other control circuit can attempt to complete the connection. Setting up a call. Calling line to relay set.- Looping of a subscriber's line 98 causes the identity of this line to be stored in preallotted register 108 via translator 124. 20 Ásecs later a new free register is allotted to the translator. Register 108 earths 118 and signals over 114 to the control circuit currently in use. 12 msec after this control ceases operations on the previous call, relay ST (F. 7) falls back, C is up and free lamp 281 lights. The calling register (or registers) now gain access to control by bringing up ST. A time-out relay MTO is prepared such that is comes up after 310 msecs unless ST falls meanwhile. The signal (or signals) on lead 114 trigger bistable circuit 258 whereby the register scanner 123 (Fig. 4) is started so as to select one of the calling registers and connect it via 109- 117 to control. Trigger 258 brings up relay PW followed by HA, PY (F. 10), 155 msec delayed TO (F. 9) and busy lamp 293. PY causes the caller's identity to be transferred over the multiples 100, 101, 102, to the marker. HA brings up MK (F. 11). With PW up and the register 108 connected, OR, OG, ISA and IS follow in that order. The marker earths the input e.g. 94 b of the A selector, corresponding to the caller's identity and wires 103, 104 from the line circuit are connected to wires 105, 106 leading to common control. At this time conductor 107 is at negative potential and wire 105 is at a potential between earth and negative battery. After a 4 msec delay therefore, gate 301 opens to trigger bistable 319. Faulty marker. If the wrong identifying relay comes up in the marker, the line circuit corresponding to this relay returns negative battery or earth over 105 depending on whether it is free or busy. For the case of earth, gate 301 is inhibited and gate 306 is opened so as to bring up fault relay FF followed by FAT and 11 msecs later RA. FAT causes SAA in the other control circuit to operate and so start a second attempt at completing the connection and RA resets the current control For the negative batery case, gate 305 triggers bistable 328 which brings up FA. FF &c. follow as before. If none of the marker relays operate, TO times-out to bring up FF &c. Assuming correct operation of the marker however, the following operations occur:-lead 104 is connected via the line circuit 5 to lead 154 wherby the relevant A group connector 48 connects the P-wires of the A links 26 to the A link selector; earth on wires 72, 74 causes the P and marking wires of B links 37 to be connected via B group connector 67 to the B link selector; and earth on wire 76 together with negative on 77, 89, 91 causes the P and marking wires of the C links 8 to be connetted to C link selector 16. Correct operation of the A, B and C connectors is denoted by negative on 92. The free/busy condition of a link is denoted respectively by negative/earth on the P wire . In the A link selector, transistor 218 is held off by earth on 135 whereby each of the 52 AND gates 177 has one input marked. Since terminal 94b is also marked, four of these gates open. The free condition of the A links is signalled via inputs, 53a to n, whereby those 1, 2, 3 or 4 free links accessible to line 98 in switch 331 are marked at the corresponding ones of outputs 95a to n. The latter are connected as inputs to the B link selector which thereupon marks at its outputs 96, the free B links accessible to the just-marked A links. Similarly the C link selector marks its outputs 97. If there are no free C links 8, 4 mesc delay circuit 294 (F. 8) causes the earth and negative on leads 76 and 77 respectively to be reversed whereby C links 7 are examined. After a further 4 msec, delay 294 restores the normal potentials on 76, 77, brings up NJ, OE and releases OG whereby C links 6 are connected to the link selector. If there are still no free links, a further set of local C links are examined and in the event that none are found free, fault relay FF &c. is brought up, (see above). However a marking on 97 (F. 8) causes clock pulses to be applied to lead 131 and relay OPK to come up. The latter (at OPK1) brings up the line circuit cut-off relay whereby lead 105 is connected to the P wire whence sensing network 278 responds to trigger bistable 334 and inhibit gate 335. A clock pulse on 131 triggers bistable 262 whereby transistor 218 in the A link selector conducts. Due to counter 199, only one of leads 187-190 is then marked whereby only one output terminal say 95b can be marked. If this output does not have access to