Patent GB-433475-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/42
Filed: 1934-02-21
Abstract: 433,475. Automatic exchange systems. MERCER, R., 5, Churchill Avenue, Kenton, Harrow, Middlesex. Feb. 21, 1934, No. 5764. [Class 40 (iv)] Arrangements are described in which an auxiliary switch common to a group of numerical selectors is employed to select an overflow line of the wanted group in the event of all the lines of the group normally accessible to the selector being busy, or to select a line of an alternative route to be used if the direct route is unavailable. In another arrangement the auxiliary switch hunts for a line of a preferential route which if available is used in place of the normal route. In general the auxiliary switch is temporarily used and the selector is reset to the line seized by the auxiliary switch. Bi - directional selector having access to groups of irregular size, Figs. 1-4. The extra lines of groups of more than 10 lines are connected to spare positions in one or more levels which accommodate groups of less than 10 lines, and these extra lines are accessible to the rotary auxiliary switch SW2 which is associable with any particular selector GS over a hunting switch SW1. Fig. 2 shows a possible grouping scheme. In order to prevent the selector hunting beyond a group occupying a part of a level, the succeeding vacant position is wired to a common busy tone set shown in Fig. 3. The auxiliary switch SW2 is taken into use when the received digit determines a group located in more than one level and the first line of the group is busy. Alternatively it might be taken into use only when all the lines of the selected level are found to be busy. As shown, the switches SW1, SW2 form a by-path link to the next switching stage, but this is not always essential. Assuming that the digit received is 2, relay G, which pulls up when the selector moves offnormal, falls back on the relapse of dialling relay C and subsequently interacts with rotary magnet RM to effect hunting, being energized by earth on the test terminal of busy lines. If the first line is busy, earth is connected to vertical wiper VW and relay 2 responds, connecting up X, which closes self-stepping circuits for the switches SW1, SW2. The former advances until the selector GS is found, when relay Y energizes, while the latter advances to an idle line of the wanted group, which is marked by relay 2 in bank 92, and relay W energizes. If the selector GS finds an idle line, earth is removed from wiper VW and the by-path link is released. If however no idle line is found, eleventh step springs are operated and relays K, V energize in series, extending the speaking and test wires over the switch SW2 to the next switching stage, while the selector GS restores to normal. The terminals of banks 94, 95 are cross-connected to terminals TB wired to impulse cams to provide for the resetting of the selector GS. The successive connection of battery to wires S, Z over suitable cams, operates relays DA, DB, and the requisite impulses are delivered to the vertical magnet VM of the selector. The removal and reapplication of battery to wire Z leads to the relapse of DA and operation of RC, U, so that impulses are delivered to the rotary magnet RM. The next removal of battery from wire Z operates relay T which by disconnecting K and V releases the by-path link and extends the connection through the selector GS, switching relay H having already operated over the test wire. Should the switch SW2 find no idle line, W fails to energize, and the operation of eleventh step springs connects back a busy signal. Instead of providing a vacant position at the end of each small group, the common apparatus may include an arrangement of the kind shown in Specification 429,767 to indicate when all lines are busy and to connect earth back over wiper VW to cause advance of the selector to the eleventh position. The switches SW1, SW2 may provide a permanent by-path for overflow calls, in which case the switch SW2 may give access to extra lines not appearing on the selectors GS, which however might be reset as long as lines to which they have access are available. P.B.X. final selector, Figs. 5-7. Each group may comprise a number of lines arranged in sequence and a number of extra lines located anywhere in the selector banks and accessible also to the rotary auxiliary switch SW21. The first line of a group is marked by battery through a resistance in bank 150, while the remaining first-choice lines except the last have their terminals in banks 148, 150 strapped together. An additional wiper 149 co-operating with the bank shown serves to initiate search by the switch SW21 over the overflow lines of a group. Assume a call to the group 19 comprising the last two lines of the first level and overflow lines locate elsewhere. If the first line is busy, relay G1 energizes over test wiper 148 and when rotary dialling relay E falls back, relay C1 energizes over wiper 150 and connects up HS which closes a fresh circuit for C1 whereby it interacts with the rotary magnet RM, relay E being in parallel with the latter. Stepping continues until an idle line is found when G1 falls back or until the last line is reached when wiper 150 is disconnected. Relay Gl on energization also closes a circuit over wiper 149 for relay 19, which as in Fig. 4 causes the switch SW11 to hunt for the selector FS and the switch SW21 to hunt for an idle overflow line in the wanted group. If an idle line is found by the selector FS, the relapse of G1 disconnects 19 and the common apparatus is released. If however the selector FS reaches the last line and this also is busy, relays K1, V1 energize, being no longer shortcircuited over wipers 148, 150, releasing the selector FS and causing it to be reset to the seized overflow line and connecting up switching relay H1 over the test wire of the seized line. If all the overflow lines as well as all the first-choice lines are busy, it may be arranged for the switch SW21 to stop in a special position and the selector FS to restore, giving a busy signal and releasing the common apparatus. Alternative inter-exchange routing, Fig. 2 (Prov.) A rotary auxiliary switch RBS is associated in common with a group of selectors S1, and on the initiation of a call selects an idle junction to a tandem exchange T terminating in a selector S2 thereat. The selectors S1, S2 receive the first digit, and each hunts for an idle junction to exchange B. If a direct junction is found by S1, then the switches RBS, S2 are released, but if no direct junction is available, S1 restores and is reset on the indirect junction selected by RBS, the latter being released. In a modification, the switch RBS selects an indirect junction when the first digit is received and sends discriminating signals thereover to bring about the selection of a junction to exchange B, the selector S2 being eliminated. Exchange routing, cutting out second selectors, Fig. 3 (Prov.). A bidirectional auxiliary switch RBS is associated in common with a group of first selectors S1 which have two sets of banks. After the first selector S1 is set, the second digit is received simultaneously by the second selector S2 and by the switch RBS, and the latter then rotates to a position corresponding to the first digit under control of a vertical wiper of S1. At least one final selector FS serving each hundreds group is wired to the lower banks of S and to the banks of RBS. Simultaneously with the hunting movement of S2, RBS operates to select a direct line to a final selector serving the same hundreds group, and if such is available, S1 and S2 are released and S1 is reset under the control of RBS to extend the connection over its lower banks to this direct line. Overflow routing, Fig. 4 (Prov.). Calls are normally set up over small capacity rotary switches S1, S2, the group to be searched by S1 being marked by a vertical wiper of a common bidirectional switch RBS. which takes the first digit. If S 1 finds no idle line, RBS hunts for an idle overflow switch OS2 having access to the same group as S2 while S1 hunts for a bidirectional overflow switch OS, which is then set on the line leading to OS2 under the control of RBS. A similar overflow arrangement may be provided at the second switching stage. The switches RBS, OS may be single-motion switches.