Patent GB-540128-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
IPC: H04Q3/42
Filed: 1939-07-26
Abstract: 540,128. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., WRIGHT, E. P. G., and LOWRY, L, P. July 26, 1939, No. 21721. [Class 40 (iv)] In a toll dialling system, discrimination between a toll call and a call local to the area is effected by an impulse regenerator in accordance with the first or first two dialled digits. In the lay-out shown in Fig. 1, a subscriber requiring a toll call dials the initial digits 91, followed by a digit C denoting the area, and the exchange and numerical digits DEFN. The A-digit switch at exchange A2, for example, has access over its 9th level to a discriminating regenerator (Fig. 2), which if the second digit is other than 1 (denoting a local call) seizes a director into which it retransmits the second and later digits, and the call is set up in the usual manner. If, however, the second digit is 1, no director is seized, and the regenerator sends out two routing digits to extend the call to the toll port or central exchange A and then retransmits the third and later digits. In response to the C digit, the incoming selector at exchange A takes into use either a regenerative code selector (Fig. 3) if the call is destined for an adjoining area C or a regenerative repeater (Fig. 4, not shown) associated with a junction to the toll port exchange B of the distant area. In the former case, a director is associated in order to route the call in accordance with the digits DEF to the required exchange C1, after which the numerical digits are retransmitted. In the latter case, a director is associated with the incoming code selector V (Fig. 5, not shown) at exchange B to route the call, and the numerical digits are retransmitted by the regenerative repeater. Both the regenerative code selector and regenerative repeater take into use a storage circuit associated with ticketing equipment and supply the called number thereto. In a modified arrangement, a discriminating regenerator (Fig. 7, not shown) on a toll call takes into use a special trunk director which supplies the complete routing number for extending the call to the central exchange of the area required. Discriminating regenerator, Fig. 2. Upon seizure over the 9th level of the A-digit switch, relay A energizes followed by B, BA, ZA and impulses over wire PU are repeated to step the 50-point receiving switch R, a condenser being charged after each digit by the relapse of C to mark a stopping point for the sending switch T. The latter normally stands in position 31, and condensers in the groups 31-40, 41-50 are charged to provide for the insertion of two routing digits when the first digit received is 1. In this case TD energizes and connects up 1G to bridge impulse springs LIS across the outimpulsing loop and to place T under the control of springs MIS. The operation of S, Z by condenser discharge ends each digit and T then goes automatically to position 41 or 1. The successive relapse of ZA, ZB measures the inter-digital pause. Since the digit 1 is not to be retransmitted, T takes one more step after reaching position 1, whereupon the retransmission of the subsequent digits stored by R takes place. Relay TDA energizes, operating SD to open the self-stepping circuit of T and connecting a tone-detecting circuit across relay 1. Relay D energizes when tone or speech is received and connects up CO which opens the P wire to release the A-digit switch. Switches R, T restore to positions 1, 31 respectively. Relay CO may also operate under the control of M in the case of undue delay between the received digits. If the first digit is not 1, relays DA, DB energize instead of TD, switch T goes at once to position 1 and MG starts tne switch DH in search of an idle director. Test relay K connects up switching relays KA, KB and all the retransmitted digits are sent into the director over wiper PU. Relay CO operates upon the release of K from the director. Code selector including regenerator, Fig. 3. When seized from an incoming selector, relays L, LR energize followed by B, BB, BC, BD, ZA, A, C, and the switches ADH, ST hunt for an idle A-digit switch and storage circuit respectively. Test relays K, KK connect up KR, KT. The regenerator differs from that in Fig. 2 in that, to give greater capacity. the condensers may be charged either positively or negatively. Each odd impulse of a train operates relays RN, RP, and each even impulse steps the receiving switch R and releases the relays. Relays CR, CA relapse in turn after each train, a condenser is charged negatively if RP is back or positively if RP is up, and R then takes one more step. The sending switch T normally stands in position 44, and a condenser of the group 45-50 is charged positively or negatively according to the level of the incoming selector in order to send into the storage circuit an initial digit to complete the called number. The switch T is advanced under the control of impulse springs MIS one step at each second impulse by means of relays TN, TP which operate alternately and send impulses to the storage circuit. When the charged condenser is reached, S, Z operate with TP up if the charge is positive or with TP back if it is negative, and T goes automatically to position 1 in which DZ pulls up, and retransmission of the digits stored by RS takes place. Relays CT, CS, which are operative during each digit, in relapsing cause T to take an extra step (corresponding to that taken by R). The successive relapse of ZA, ZB measures the inter-digital pause. The three exchange digits are sent at springs LIS to the A-digit switch and director, which emits a number of routing digits over the out-impulse circuit, the first being repeated by A to set the selector in the usual manner. The A-digit switch and director then release, and K, KR fall back leaving the forward connection under control of springs LIS. The digits sent are counted by a switch DS controlled by CS, and after the last exchange digit, TH energizes and prevents sending of the numerical digits until KR is back. When the switches R, T are in alignment, Z is held and ZA is back. Upon reply, relays D, DD energize and connect a ground to the storage circuit which then receives the calling number over a simplex circuit in response to a backward tone signal. The storage circuit completes its record upon release when LR cuts off the ground. On a call originating in another area, DT energizes and prevents the seizure of a storage circuit. In this case, the switch T goes at once to position 1. Regenerative repeater, Fig. 4 (not shown). This is associated with a junction outgoing to another area and is seized by an incoming selector or local selector at the toll port exchange. The regenerator acts in the same manner as in Fig. 3, and sends the digits over the junction and when necessary to a storage circuit, the latter receiving also an initial digit depending on the level of the selector. Backward reversals over the junction prevent the sending of the exchange digits until the incoming selector has seized an A-digit switch and of the numerical digits until the director has emitted the routing number. Modified discriminating regenerator, Fig. 7 (not shown). Upon seizure by the A-digit switch, the incoming digits are recorded as in Fig. 2. If the first digit is 1, a trunk director is seized, the sending switch (which normally stands in position 1) first takes one step to absorb that digit and then transfers the exchange digits to the director. The latter emits the routing number and then releases, whereupon the stored numerical digits are retransmitted by the sending switch. If the first digit is not 1, a regular director is seized and all the stored digits are sent thereto, the routing number and numerical digits being emitted in the usual way.