Patent GB-794819-A (GB)
Title: Improvements in or relating to automatic telecommunication exchanges
Inventor: HARTLEY GEORGE CLIFFORD
IPC: H04Q3/00
Filed: 1956-08-03
Abstract: 794,819. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Aug. 3, 1956, No. 23985/56. Addition to 794,820. Class 40 (4). In an exchange as claimed in Claim 1 or Claims 1 and 3 of the parent Specification, each subscriber's line circuit is connected directly to one of the inlets to the odd number of stages of coordinate multi - switches and to one of the outlets therefrom. As shown, there are three stages of multiswitches constituted by the A, B and C frames, respectively. Initiation of a call by subscriber SS1 causes a change in condition in his line circuit LC1 which results in the seizure of his inlet to an A frame multiswitch A1. Each A frame outlet is connected to a first link, e.g. IL, and the first outlet from the caller's A frame multi-switch having access to a free first link is selected, the multi-switch being automatically operated to extend the calling line to that free first link, say IL. The seizure of the first link marks the relevant inlet of a register hunter RH, an outlet of which having access to a free register is selected, and the register hunter associates that register with the calling first link. Dialling tone is reverted from the register, say REGA, which then receives the dialled digits, preferably in the manner described in the parent Specification. The call distributer CD scans the registers and when it finds a register with a wanted number stored therein, signals that register to set up the call, provided that no other register is controlling the setting up of a call at that time. The register then transmits the wanted number to the called line marker CLM (common to the whole exchange) in the manner described in the parent Specification, and at the same time signals the calling line circuit LC1 to cause it to be momentarily disconnected from the A frame multi-switch, whereupon the seized first link and register are released. The signal operates a special relay (not shown) in LC1, which in turn signals the route selector RS over a lead L1 common to all the line circuits connected to the same multi-switch Al. The called line marker energizes a lead corresponding to the thousands/ hundreds digit combination of the wanted line, and one corresponding to its tens/units digit combination, as described in the parent Specification, thus opening a gate controlled by these two leads in the called line circuit. This circuit then marks an outlet from a C frame multiswitch to which it is connected, and applies a signal over a lead such as L2, individual to that C frame multi-switch, to the route selector RS, which then knows which A frame switch and C frame switch are to be interconnected. The route selector includes a gating network fed with information, as to which outlets from the A frame switch and which inlets to the C frame switch are free, over leads such as L3, L4 from the first and second links, and proceeds to choose a free path between the A and C frame switches whereby an nth A frame outlet and an nth C frame inlet are to be connected via an nth B frame multi-switch. This is done by energizing a lead such as L3 for all nth A frame outlets, the coincidence of this marking and a calling condition recorded in a line circuit connected to an A frame multi-switch as a result of the signal from the register causing that line circuit to be connected to the nth outlet of its A frame multi-switch and hence to a first link; the caller thus being extended to a B frame inlet. The route selector also marks all nth C frame inlets over a lead such as L4 so that a B frame multi-switch has an inlet engaged by the seized first link and an outlet marked over the lead such as L4. This multi-switch operates and extends the caller to the marked second link and thence to an inlet of the C frame multi-switch to an outlet of which the wanted line is connected. This C frame multi-switch operates to complete the connection to the wanted line circuit. The called line marker and route selector are released and the called line is rung. This method of operation in which a call is set up in a short period T (see parent Specification) assumes that the switches are electronic. If, however, crossbar multi-switches are employed the modified method described in Specification 794,818 is used, wherein the markings over leads L3, L4 are recorded in the links and the route selector is then released. The call is then set up independently of the route selector, each multiswitch being busied as soon as an inlet or outlet thereof is marked and maintained so until the switch setting operation is completed.