Patent GB-1136792-A (GB)
Title: Communication switching systems and networks
Inventor: SINGER FREDERICK LAWRENCE
IPC: H03K17/82
Filed: 1966-03-15
Abstract: 1,136,792. Automatic exchange systems; transistor logic circuits; circuits employing magnetic storage elements. WESTERN ELECTRIC CO. Inc. 15 March, 1966 [16 March, 1965], No. 11224/66. Headings H3B, H3T and H4K. In a multistage ferreed switching network, each interstage link is provided with a transfluxor which is set to a busy state in response to a signal occurring on the link control wire when the ferreeds at each end of the link are operated and which is set to a free state in response to a signal over the link speech wires when the connection established via that link is terminated. Since ferreeds are not released immediately on termination of a call, the last mentioned signal occurs as a sudden increase of current transmitted in the same direction over the tip and ring wires from the exchange control circuit when the latter's line scanner detects an open loop condition at the end of a call. The threading of the various conductors through the three apertures of a transfluxor is depicted in Fig. 2 (not shown). Switching network.-This is a conventional three-stage network having four 8 x 4 ferreed matrices in the first and last stages and four 4 x 4 such matrices in the second stage, the trunking being such that each inlet has access to each outlet via four possible paths. One end of each of the row and column windings is connected to a respective common bus in each matrix. In any matrix of the first and third stages, the row and column busses are permanently connected but in the second stage matrices connection is established via a relay contact such as LA1 (Fig. 4), the operation of which is discussed below.  Transfluxor memory network.-The transfluxors threaded by the primary links are arranged in a rudimentary matrix (see Figs. 4 and 5) with common interrogate conductors, e.g. 501 threaded through like-numbered transfluxors associated with each second stage matrix and with a common output conductor, e.g. SW10A threaded through all those transfluxors associated with the same secondary matrix. The secondary-link transfluxors are similarly arranged, also with respect to the secondary matrices. In addition to the interrogate and output windings, each transfluxor's B aperture is threaded by a D.C. priming winding. The set or busy state winding which forms part of a link control wire is threaded through the A aperture. The reset or free state windings, which are constituted by the speech wires (over both of which a high value current pulse in the same direction is passed for resetting purposes) are threaded through the central aperture. Operation.-In response to a calling line, e.g. a in switch No. 1 of the primary stage requiring access to outlet 1 of switch No. 3 of the tertiary stage, relays P1 and SL4 (both not shown) are operated. Thereafter, an interrogate pulse is passed, from pulse generator 500 over leads 501 and 502 in series, to ground at 801. Consequently, those transfluxors which correspond to idle links, provide no output pulse on leads SW(10-40)A and SW(10-10)B. corresponding SWA and SWB leads are connected as two inputs to a three-input logic circuit (see below) which provides an output only if neither lead carries a pulse, i.e. it is ascertained that both a primary link to and a secondary link from a same secondary switch are available to the connection. A transistor/ relay lock-out chain (Fig. 10, not shown) then selects the lowest numbered secondary switch for the connection by operating a contact such as LA1. Since inlet marking contacts LP1-1 and outlet marking contacts TP1-3 are closed, closure of LA1 allows a ferreed operating pulse to pass from pulse source 401 via the three effectively selected ferreeds in the switching network to earth on the common outlet marking bus. The transfluxors on the inlet and outlet sides of the first secondary switch are set to their busy state by this operating pulse and the connection is established. Release.-When the call is terminated, central control pulses the speech wires so as to reset the transfluxors to their idle state. The ferreeds are not restored however, until one only of their row and column windings is pulsed during the establishment of a subsequent call. Logic circuits.-A transistorized pulse generator/pulse shaper, which is triggered on by a signal akin to that produced by relay contact chatter, is described with reference to Figs. 7 and 8 (not shown). Fig. 9 (not shown) depicts a NAND logic circuit in which an input pulse on PRE is transmitted through the output terminal unless a pulse occurs on either input A or B. If such a pulse occurs, capacitor 905 effectively lengthens it and causes transistor switch 903 to close thereby short-circuiting the pulse on PRE to earth.