GB604593A - Telephone exchange systems - Google Patents

Abstract

604,593. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. April 13, 1945, No. 9287. Convention date, May 15, 1944. [Class 40 (iv)] In a system using finder switches in order to reduce hunting time, a plurality of finders serving a given group of lines is divided into sub-groups, there being a set of finders corresponding to each sub-group, each having a normal position immediately preceding that sub-group. A finder normally hunts only in its corresponding sub-group, but may be seized for hunting in succeeding sub-groups if all the finders for those sub-groups are in use. The invention is described in relation to a set of 100 lines divided into four groups, each having three corresponding line-finders and is applied to a system similar to that described in Specification 628,174 in which line-finders and first selectors are connected by B-links which are sought for by R-links whose hunting is initiated by the incoming call. Operation of the subscriber's line relay LR, Fig. 3, in group 1-25 operates relays CSR1, CSR2, Fig. 4, which operate the start relays LSR, Fig. 5, of all the R-links, Fig. 5, which hunt for a B-link (Fig. 6) having on its T-terminal battery applied by LR via resistance R1 and the X wire. Relays T1R, T2R of the R-link first finding the marked T-terminal operate and low resistance earth applied through coils of T1R and T2R busies the B-link and shunts down CSR1 to stop the other R-links hunting. Relay T2R initiates the association of a register-controller with the R-link and the B-link then sets the finder hunting for the calling potential PC applied to the T-wire by relay LR, under control of the register-controller, all as described in Specification 628,174. If all the (3) B-links appropriate to the group 1/25 are busy, wires Y and Z will be connected together over the contacts, in series, of all the BRR relays in the group and the marking potential will be applied to the B-links of the next group (26/50) (see Fig. 4), one of whose associated finders then hunts for the calling line, though now having to pass over lines of its own group before reaching the group containing the calling line. Likewise, the B-links of succeeding groups are brought in if all B-links of preceding groups are in use. Specification 558,416 also is referred to.