Patent GB-458436-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1935-06-20
Abstract: 458,436. Automatic exchange systems. VRIES, W. C. DE, 25, Koningin, Emmakade, The Hague. June 20, 1935, No. 17762. [Class 40 (iv)] Inter-exchange connections are set up entirely over four-wire circuits from the initiating to the terminating exchange. The two to four wire terminal circuits are not individual to the four wire inter-exchange junctions but are connected up by group selectors with four speech wipers or by a pair of linked selectors, the inter-exchange connections being set up over similar switches. A.C. impulsing and supervision is utilized, the release signal being repeated forward at each exchange and a holding signal transmitted backward from each exchange in response to the release signal until the terminating exchange is reached, whereupon the holding signal is removed in turn from each exchange backwards. In the system described, a two to four wire terminal, Fig. 5, is taken into use by automatic switches at the originating exchange and a selector, Fig. 6, in response to the next digit selects an idle outgoing four-wire circuit, Fig. 4. The incoming four-wire circuit, Fig. 2, at the next exchange is associated with a switch, Fig. 3, which is caused to seize either a further outgoing four-wire circuit, Fig. 4, or a local four to two wire terminal, Fig. 7, if the call is to terminate at that exchange. Numerical or non-numerical switches may be interposed between the switches shown and the outgoing four-wire circuits. The signal receiver in the four-wire circuits are used for the backward holding signals as well as for forward signalling. Outgoing call, Figs. 5, 6 and 4 in this order. If the switch, Fig. 6 is idle, relay N in the terminal apparatus is operated over off-normal contact rand C is operated over the incoming c wire when the terminal is seized. D pulls up and operates relay C at the switch to prepare its test circuit. Incoming impulses over the d wire are repeated by I to the impulse relay A of the switch which responds and hunts in known manner, relay T operating and switching through when the outgoing end of an idle four-wire circuit, Fig. 4, is encountered. When the switch goes off normal, N falls back and when hunting starts, a secondary off-normal contact o opens the impulse circuit to A (the fourth wire of this switch is not used). When the outgoing end, Fig. 4, of the four-wire circuit is seized, C pulls up followed by F and P pulls up in the return path in a loop circuit over choke Sm2, Fig. 5, and operates Q. Relays P and Q remove attenuation pads which are only required at a tandem connection of two four-wire junctions. Subsequent impulse trains are repeated by I in the form of A.C. impulses over the go path. Setting up connection through tandem exchange, Figs. 2, 3 and 4. The incoming A.C. impulses over the go path pass over leads s1, s2 to a receiver which, in response, connects ground impulses to lead s3. Relay N is normally operated if the switch, Fig. 3, is idle. The impulses are repeated by I, subject to correction by G and H in a manner not described, to impulse relay A of the switch, C, Fig. 2, operating on the first impulse and locking up. The switch operates as described for Fig. 6, and seizes the outgoing end, Fig. 4, of a four-wire junction to the next exchange. A non-numerical switch or a further numerical switch may be interposed between Fig. 3 and 4, and if the switch is numerical it is set by impulses repeated by I over the d-wire Relays C and F, Fig. 4, are operated as before but in the present case P and Q are not energized since there is no low resistance loop in Fig. 5. Incoming call at terminating exchange, Figs. 2, 3 and 7. The incoming circuits, Figs. 2 and 3, respond to A.C. impulses in the same manner as described for the tandem exchange but the switch, Fig. 3, is directed to a group of terminal equipments such as Fig. 7 leading to the two-wire circuits. When the terminal is seized, C and F pull up and subsequent impulse trains are repeated by I over the d-wire. Reply signalling. The response of the called party is indicated by a ground pulse over the d-wire which operates S followed by E, Fig. 7, in the wanted exchange. Relay S sends an A.C. signal over the return path and E closes the go path which is normally open at this point to prevent impulses from affecting the return path and to obviate singing of the four-wire channel. The A.C. reply signal pulse passes to the originating exchange where receiver S.O, Fig. 5, operates relay S which repeats the signal as a ground pulse over the d-wire to the two-wire circuits. Relay V(i) operates, locks, removes choke Sm2 from the return path and also closes a contact in the go path which is normally open so that signal receivers in that path are not subject to interference from the two-wire circuit. Release. When the calling party replaces his receiver, the switches preceding the terminal apparatus, Fig. 5, at the originating exchange release and the consequent removal of ground from the c-wire releases C so that O pulls up [V(i) is operated] inserts choke Sm1 across the go path and connects V(ii) to the back signal receiver S.O. Relay D falls back slowly and I pulls up and holds dependent on slow releasing relay V winding (i) of which is now open. Relay I transmits continuous A.C. over the go path which at the incoming circuits, Fig. 2, at all exchanges causes the signal receiver (s1-s3) to apply continuous ground to I. Correcting relays H and G follow and G holds to s3 and shunts down C but in the meantime V(i) pulls up and operates O so that V(ii) holds to the ground on s3. Relay O also inserts a choke across the go path, switches the signal receiver over to the return path and as S has been operated by the relapse of C, continuous A.C. is transmitted back over the return path. It will then be seen that V(ii) at each exchange except the last, is held by the backward A.C. signal from the succeeding exchange. The insertion by the relays D of chokes across the go paths operates K, Fig. 4, in the outgoing four-wire circuit at each exchange, relay K maintaining the forward release signal and releasing F. At the last exchange the operation of the K relay, Fig. 7, also releases F which opens the circuit of S to prevent this relay applying a backward A.C. signal and consequently V(ii) at the incoming circuit, Fig. 2, of the last exchange does not hold V so that C, Fig. 3, releases and the switches at the last exchange restore. N, Fig. 2, at this exchange therefore pulls up over off-normal contact r and releases S to remove the backward A.C. from the junction to the preceding exchange. The relay V(ii), Fig. 2, at the preceding exchange is thus released and the associated switch, Fig. 3, restores, and K, Fig. 4, in the outgoing circuit releases to disconnect the forward A.C. Release thus proceeds backwards to the originating exchange where the relapse of V(ii), Fig. 5, releases the outgoing switch, Fig. 6, and other operated relays fall back. Dealing with faults; ensuring release. If due to an interrupted circuit (blown fuse at a switch), relay K at outgoing circuits, Fig. 4, is not operated over its line winding during forward release signalling so that such signalling is not repeated forward in the normal manner, F holds over (ii) in series with K(ii) which forwards the signal. After a delay, thermal relay Th1 shunts down F(ii) and releases K(ii). If due to faulty release of a switch, the backward holding signal is not removed, thermal relay Th2 pulls up and operates Q(ii) in series with K(ii) so that the return leg of the outgoing circuit is short circuited which is equivalent to removal of the holding signal from the succeeding exchange. C, Fig. 4, releases when the switch, Fig. 3, restores, and Q(ii), K(ii) hold-over key Sp, the circuit being barred by the opening of the C-wire.