Patent GB-957477-A (GB)
Title: Telephone switching systems
IPC: H04Q3/00
Filed: 1961-09-21
Abstract: 957,477. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Sept. 21, 1961 [Oct. 31, 1960], No. 33796/61. Heading H4K. In a universal concentrator system employing magnetically latched cross-bar switches and cut-off relays in the remote unit and in the control unit at the exchange, wherein at the end of a call a line remains cut through, i.e. connected through a trunk to the control unit, means is provided in the control unit for identifying the line connected to a trunk prior to effecting disconnection of that trunk. Whenever the number of trunks cut through in a group of ten trunks exceeds four, sufficient trunks are released to leave only four cut through. A trunk to be released is selected and ground is connected to its sleeve, whence it is extended via the operated sleeve crosspoints of the crossbar network in the control unit to a sleeve relay individual to the line cut through to the trunk in question. Operation of this sleeve relay identifies the line and causes signal relays to transmit the identity to the remote unit, whereafter a signal is transmitted over the trunk to enable the cut-off relay at the remote unit and to release the hold magnets at the remote unit and in the control unit, thus freeing the trunk and the line for further calls. Signalling between the remote and control units.-This is effected over two signalling pairs TSO, RSO and TS1, RS1. A signal circuit 110 at the control unit includes a sensitive relay 13S2 and a marginal relay 13S1 connected in series to conductor TSO and a similar pair of relays 13S4, 13S5 connected to RSO, corresponding relays 7S2, 7S1, 7S4, 7S3 being provided in circuit 114 at the remote unit. Minimum current in one of the conductors TSO, RSO operates the sensitive relays only, a greater current operating the marginal relays as well, so that in all nine signals are available for signalling digital information. The identity of a line is sent in terms of three digits in the 100-line embodiment described, the first digit indicating line group 0 or 1 (i.e. lines 00-49 or 50-99) and a connect or disconnect indication, the second the " B " part of the line number (one of nine signals), and the third the "A" part of the line number (one of six signals). A fourth digit indicates the trunk number (one of nine signals). As in the embodiment two groups each of ten trunks are provided an auxiliary signal is sent over the pair TS1, RS1 to indicate the tenth trunk. This pair is also used to signal the advance of the sequence control at both units, for checking purposes, and for release indications. Originating call.-The line relay individual to the calling line operates in circuit 104 and brings up two relays in line lock-out circuit 118, one identifying that one of twelve sub-groups to which the line belongs, and the other which of the nine lines in that sub-group it is. Low resistance ground is thus connected to TSO or RSO according as the line is in group 0 or 1, and as a result the group relay is operated in preference control circuit 109. Assuming this call to have preference, a relay is operated in the master signal control circuit 113 to initiate a mark signal and to operate a similar relay in the remote unit. The register relays in registers 107 and 117 store the information received by the signal relays and, after checking, the checking circuits 116 and 111 release the mark and signal relays and advance the sequence relays of sequence control circuits 115 and 112 one step. The signal circuits 110 and 114 are then energized in accordance with the " B " portion of the line number, this information being registered and checked and the sequence control circuits being again advanced. The "A" portion is sent in like manner. Direct ground is then connected to the signal relays in remote circuit 114 to place the signal circuits 110, 114 under control of the trunk selection relays of circuit 108 and the number of the selected trunk is sent to the remote unit and registered. Trunk numbers "0"-" 8 " are sent over TSO, RSO and registered directly on the register relays, but for-trunk number "9" a preliminary signal over RS1 brings up a transfer relay in register circuits 117, 107 to convert a trunk "0" indication into a trunk "9" indication. Checking circuit 116 ensures that the information in register 117 is the same as that in the lock-out circuit 118. The control circuit connects the trunk to the line terminals at the exchange and releases and consequently disables the cut-off relay at the control unit. The select magnets in networks 101, 102 are operated, the cut-off relay in circuit 104 is released and consequently disabled, and the hold magnets in networks 101, 102 are then operated. Terminating call.-This is set up in like manner, cross connections from the sleeve relay to lock-out chains in circuit 105 identifying the wanted line, and the lock-out circuit 118 being disabled while the call is set up. Disconnecting an established connection.-A disconnect request for an individual trunk is initiated if the trunk hold magnet is operated (line still cut through), the trunk busy relay is unoperated (trunk idle), and the trunk load control relay (not shown) in circuit 106 is operated (more than four hold magnets operated). The disconnect control circuit 106 then opens the circuits of all sleeve relays towards the exchange and connects them to the associated control circuit sleeve leads. Trunk selection circuit 108 then selects one of the trunks for disconnection, and grounds its sleeve, thus operating the sleeve relay of the line to which the trunk is connected. The lock-out relays in circuit 105 identify this line. The line and trunk members and a disconnect indication are sent to the remote unit. The cut-off relay in circuit 104 is thus enabled and the hold magnets in networks 101, 102 are released. Permanent loop condition on a line.-Such a line is denied service by causing disablement of its cut-off relay in circuit 104 under control of the control unit at the exchange. U.S.A. Specification 2,636,931 is referred to.