Patent GB-991553-A (GB)
Title: Telephone switching systems employing electro-mechanical switches
IPC: H04Q3/54
Filed: 1961-08-22
Abstract: 991,553. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. Aug. 22, 1961 [Aug. 31, 1960], No. 30243/61. Drawings to Specification. Heading H4K. A telephone switching system comprising a switching network having electromechanical switches interconnected to form links of a network, includes storage devices for temporarily storing switch control signals, gate devices being connected between the storage devices and a common signal path conveying signals from a common control circuit, the gate devices being operable to connect selected storage devices to the common signal path. As described the switches are cross-bar switches of the type in which a connection between an input and an output is effected by operating two select magnets (one out of a group of three and another out of a group of seven) followed by a hold magnet, the operating current for all these magnets then being cut-off, the select magnets thereupon releasing, but the hold magnets being retained by remanence. They are subsequently released by a reverse current. The invention is described in relation to a system in which subscribers' lines are connected via line link frames to junctors and thence via trunk link frames to intra office trunks. Each frame consists of two stages of cross-bar switches, the setting of the first stage in the line link frame being described in detail. This stage consists of five levels each consisting of up to eight units each consisting of a 20 x 20 switch, the 20 outputs of the switches of each level being multipled over the units and crossconnected to the second stage switches. Each level thus serves up to 8 x 20 subscribers. The subscribers are associated with the hold magnets and the outlets to the second stage of the frame are associated with the appropriate combination of select magnets. Each frame has its own set of storage relays which are connected to the common control circuit by means of gate relays. When a connection is to be established the control circuit operates the appropriate gate relay which then signals the control circuit to emit signals on the appropriate control wires. The signals are then recorded on the storage relays which lock up. The signals stored are the level identity on one of five relays; the unit identity on one of eight relays; the identities of the two select magnets on two out of ten relays; the identity of the hold magnet as a combination of two relays one of a group of five and the other of a group of four; two relays for indicating whether the first or second stage switch is to be controlled; and two relays indicating whether the control is the operation or release of the switch. When all these relays are set, earth is reversed to the control circuit to indicate that it may now proceed with another call. This earth also brings up a frame busy relay. The control circuit then releases the gate relays. The select magnet storage relays operate corresponding select magnets in all the switches whereupon the hold magnet determined as above from the stored hold magnet and unit identity. When this magnet operates a relay in its operating circuit also operates to energize a slow to operate relay which gives the hold magnet time to saturate, after which it operates a frame release relay which releases the storage relays. Release is effected similarly except that with a release indication stored opposite polarity is applied to the hold magnet and no delay is interposed before the frame release relay operates. Specification 904,164 is referred to.