GB847234A - Improvements in or relating to time division multiplex circuits - Google Patents

Abstract

847,234. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. May 31, 1957 [June 5, 1956], No. 17396/56. Addition to 822,297. Class 40 (4). In an exchange in which groups of subscribers are served by individual time division multiplex highways, two different channel time positions are used for a connection between subscribers of the same group and storage capacitors are used as described in the parent Specification. The control circuits for inter group connections are similar to those described in Specification 765,681. As shown in Fig. 3, subscribers' line groups P, Q, R &c. each have access to all other groups over links p, q, r, &c., each link providing the route for all calls incoming to a particular group. A connection between subscribers X1 and X2 of the same group P is made by operation of gates GX1 and GS in one channel position and gates GX2 and GS in another channel position. The gates to subscriber's lines of each group, and to storage capacitors, are controlled by stores MA, MB, and access selectors SA, SB. Ferromagnetic matrices may be used for the stores and access selectors MA and MB having rows which are read out cyclically and correspond to channels in the multiplex highway of the group of subscribers served by the stores. An additional store MC and access selector SC controls the gates between group highways and inter-group links. A connection from subscriber X1 of group P to subscriber Y of group Q is made over the same channel time position in the highways of both groups. A register controls gates GX1 and GQ to gain access to the wanted group Q over the link q by means of an initially seized channel position in the highway of group P which, if not idle in the highway of group Q, is replaced by one free in both groups. The free channel is recorded in matrices MA and MC to operate gates GX1 and GQ of group P while matrix MA of group Q operates gate GY in synchronism. It is possible to connect subscribers of different groups by using different channel positions in each group. Thus, for one channel position the calling subscriber's line gate and the gate to the link of the wanted group are opened coincident with the gate of the storage capacitor of that group, while at a later channel position the called subscriber's line gate and the storage capacitor gate are opened. The number of links may be reduced if gates are provided between each link and every group, it being necessary however in this event to seize a link and discover an idle channel therein for each call. Fig. 4 (not shown), has the storage capacitors of each group associated with the link serving that group, the link being separated from the group highway by means of a gate. To select a storage capacitor from those associated with a group, each capacitor is identified by a serial number and a search is conducted in the matrix MB for consecutive serial numbers until no match is found. The stores MB and MC may be combined and by means of a single access selector control all group and storage gates. To facilitate maintenance each group of subscribers' lines may be connected to the inter-group links over two sets of line gates and two multiplex highways in parallel so that one highway may be withdrawn without disconnecting the group.