744,123. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. May 29, 1951 [May 31, 1950], No. 13536/50. Class 40 (4). In a modification (not shown) of the system described in Specification 744,121, two-motion switches are used as responders in the first two stages to respond to one digit and to hunt for a free responder in the next stage. A single twodigit switch responds to the last two digits. In another modification, Figs. 4, 5, 6, hunting between stages in the impulse responder is eliminated. The responder switches are arranged so that a route through them may be selected by means of a route finder and control switches, on which switches the digits of the wanted number are stored. Another system includes a satellite exchange. The conversational switches may be relays, cross-bars, wiper switches or gas discharge tubes. The system is described in general terms, the details being substantially as described in the Specification referred to. The two Specifications use the same prefixes for corresponding parts. When a call for a station SS, Fig. 6, is extended from line No. 1111, Fig. 4, through finder-final PXFF and second finder Pp2F to busy-feed equipment PpBF, a selector IRHS hunts for a free impulse responder IR, eight responders being available to a group of 500 lines. The speaking leads SL are extended to an impulse steering device ISD and the digits are stored in registers ExA, ExB, ExC (A, B, C digits) and 1ND, 2ND, 3ND, 4ND (numerical digits). Translation of A, B, C digits into routing digits. Switches A, B, C are operated tandem in accordance with the digits stored in ExA, ExB, ExC and the C switch picks up markings identifying the routing digits. Each switch A is individual to 500 lines and switches B, C are common to the whole exchange but the B switches may be individual to 2000 or 5000 lines. As soon as the A, B, C digits have been registered a route finder RRF selects a route through two switching stages AR, BR in accordance with the A digit stored in ExA and the BR switch is operated over OLB, OLBR in accordance with the B digit stored in ExB. Three routes may be provided by each set of switches A, B, C and AR, BR. References for test leads, test relays, common test leads, hold leads and operating leads include the prefixes TL, ST, CTL, HL and OL. Relay R1R operates in the lead OLBR and connects battery to common test lead CTLR to start a second route finder ABCRF which employs AR, BR as control switches to select a route through the A, B, C switches. The C switch is operated over OLC in accordance with the C digit stored in ExC. In general a route finder employs n - 1 control switches to mark numerical groups of switches in n - 1 switching stages through which a route to an nth switching stage is to be selected. The nth switch is set by an nth register over the route selected. Each outlet of C comprises three wires RD1, RD2, ABC. Routing digits are marked on RD1, RD2, as pulse positions in a pulse cycle by means of a distribution frame DF and the repetition of digits to tandem and terminal exchanges is controlled by a potential on ABC. The routing digits are stored in registers ExRD1, ExRD2 which are operated over RD1, RD2. If a called line is busy, a breakdown relay BD brings about the release of the responder and the transmission of busy tone from PpBF. Local calls involve only one routing digit which is stored in ExRD1. When the fourth numerical digit is stored in 4ND, battery is connected to common test lead CTLX by impulse steering device ISD and route finder RFX selects a route through numerically marked switches ERDX, 1DX. to 2DX and 2DX is operated over OL2D, OL2DX in accordance with the digit stored in 2ND. In a similar manner, a second route finder RFR selects a route through numerically marked switches ExD1R, 1DR, 2DR to 3DR, the last switch being set over OL3D, OL3DR by 3ND. As there are three routes through the switches ExD1R &c. allotted to a 100 lines, and as route finder RFR is common to 500 lines, RFR has to select one route from 15 routes. However, relay HD operated by the selector IRHS over lead IHD only applies testing battery for the three routes available to the calling 100-group. Finally, a third route finder RF selects a route through marked conversational switches in ExD1, 1D, 2D, 3D to FF and the switches are set in accordance with the digits stored in registers ExRD1, 1ND, 2ND, 3ND, 4ND. The final finder FF is set by 4ND over BTFF. Inter-exchange calls involve two routing digits stored in ExRDI, ExRD2. Route finder RFX selects a route through ERDX only, under the control of ExRD1. The second route finder RFR selects a route through ExD1R, ExD2R in the group marked by ERDX, and ExD2R is set over RFX, RFR, ExD1R by ExRD2. The third route finder RF selects a route to a junction hunter JH through conversational switches in ExD1, ExD2 marked by ExD1R, ExD2R. The junction hunter hunts for a free junction JL and in accordance with the potential marking on wire ABC in the distribution frame DF, OS determines whether the numerical digits are transmitted alone or preceded by the ABC digits. Satellite exchange, Figs. 9, 9A. A system using one exchange digit and four numerical digits may include a satellite identified by three digits 21A (one exchange and two numerical, A being any digit from 3-0) which are the first three digits of all stations on the exchange. The exchange includes a dial repeater JDR, a second responder finder 2FR and digit responder finders, Fig. 8 (not shown). A discriminator DE (Fig. 9) in the impulse responder steers the dialled digits either to a main exchange or to the local digit responders, by operating one of the relays JSR, DA. A line relay A responds to impulses on the speaking leads SL extended through the impulse responder finder 1RF. The usual B, C relays are supplemented by an auxiliary change-over relay CC. Impulses are repeated by A to counting relays R 1, R2 ... RA and over a back contact of relay DA to the dial repeater JDR, the dial repeater being out off when DA operates. Relay C marks the digits in the repeater over MML. Whenever the impulses of a digit are counted the last counting relay operated remains locked to CC, but falls back with CC soon after, in readiness for another count. If the digits 21A are received, relays D2, D1, DA are operated over the left-hand contacts of R2, R1, RA. Relay DA opens the impulsing circuit to JDR which restores to normal and prepares relays 1S3, 1S4 to count the third and fourth digits. The third numerical digit is transmitted via the second numerical digit responder 2DR to the third, 3DR (not shown), and the fourth numerical digit is transmitted to the fourth numerical digit responder 4DR. Relay JSR operates and locks if the first three digits are not 21A. Whenever JSR operates the impulse counting circuit is disabled and connects battery to common test lead CTL to select a free junction to the main exchange. Relay ST operates momentarily and relays SS, TR follow. Relay SS locks but TR releases after an interval during which a junction may be seized and signals the dial repeater JDR over TML to transmit the impulses over OL to the outgoing junction line through 1RF. The equipment is released and busy tone is returned to the calling party under the control of a breakdown relay BD. Specifications 652,881, 656,559, 665,129, 679,544, 744,122, 744,124 and 744,125 also are referred to. Reference has been directed by the Comptroller to Specifications 656,559 and 665,129.