Patent GB-692412-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
Inventor: HARTLEY GEORGE CLIFFORD
IPC: H04L12/00
Filed: 1948-04-30
Abstract: 692,412. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd. April 29, 1949 [April 30, 1948], No. 11841/48. Class 40 (iii). A telegraph exchange system comprises equipment for transmitting a station identity signal twice in different but related forms, equipment for receiving and recording said two forms, equipment for comparing said records one with another and control equipment for exercising different control of subsequent operations accordingly as the records agree or do not agree. In the embodiment described this double transmission is employed on junction calls. Local call; register storage. When the calling subscriber depresses a call key he starts a line-finder at the exchange which connects him to a register shown diagrammatically in Figs. 7A ... 7C. When his supervisory lamp then glows he sends the wanted subscriber's three-digit designation in five-unit code. The three digits are repeated by a register relay TRA (Fig. 7A) and stored in succession on cold-cathode tubes SXA ... MXE, SYA ... MYE and SZA ... MZE respectively, the S tubes firing for spaces and the M tubes for marks. The storage is controlled by a timebase and counting-chain UDA ... UDG, started by a relay TRB in parallel with TRA, as described in Specification 657,760, and also with reference to the present, Figs. 5 and 6 (not shown). When the last digit has been stored relay CC operates and connects reading tubes SRA ... MRE (shown in Fig. 7B) to the cathodes of the corresponding first-digit storage tubes SXA ... MXE and those reading tubes corresponding to stored spaces fire and operate marking relays MA ... ME. The operated contacts of these relays connect a selected one of ten A.C. phases #1 ... #10 to a transformer TP (Fig. 9). Local call; group selector operation. When the register was seized by the calling subscriber a relay ST, Fig. 4A (not shown), operated and at st8 (Fig. 9) operated STD, which in turn at std1 put earth on lead a over a delay coil FS. This earth now operates over leads a and SA (Fig. 3A) a relay GA which at ga2 completes the group-selector drive circuit to the latch magnet GLM over lead c (Fig. 3A), lead c (Fig. 9), sr2, std4 up, tal, and st5 up. The groupselector therefore hunts for the selected phase marking on arc e and when this is found e.g. over fa5 it is applied over leads RA and b to a second transformer TQ. Until this required outlet is found there will be a phase - difference in the secondary circuits TP, TQ, which will fire the cathodes of SV1 on alternate halfcycles, a cathode-ray network maintaining the point P at a steady negative potential. The correct outlet now being found and the phase-difference thus being removed, SV1 no longer conducts, the potential of point P rises and SV2 conducts, operating WP over std2 up. At wp1 test relay PTA is connected over lead d to the test-level d (Fig. 3), and if the wanted outlet is free the battery operates PTA over fa4, which at pta 1 removes the short-circuit from PTB. This operates, releasing WP, extinguishing SV2, and operating TA, which at ta1 stops the selector. At ptb1 a relay SR operates which at sr3 removes earth from the a lead, allowing GB (Fig. 3) to operate in series with GA, and thus switching the calling circuit through to the final selector at gb1 and gb2. If the outlet tests busy, i.e. there is no battery on the d lead, PTA will not operate and the selector continues to hunt until a free outlet is found or the complete group of outlets belonging to the wanted digit has been searched. In the latter case the selector finds on the next contact of the d arc permanent battery, while on the e arc contact there is permanently each of the possible phase markings. WP operates to the correct phase as before, and at wp1 BR operates to positive battery, rectifier MR13 preventing PTA or PTB from operating. At br1 the relay SR is disconnected and therefore remains normal to prevent switching through of the line, and relays OCC and TA operate in series, the former connecting a machine code generator to the calling subscriber to send the signal " OCC " and the latter stopping the selector. The common generator generates continuously a start or S pulse, then concurrently all the required supervisory signals, followed by a stop or Z pulse. The S pulse operates a relay SP, Fig. 4B (not shown), over contacts of which the signal OCC is connected to line. The subsequent Z pulse operates a relay ZP, and in turn Z, Fig. 4A, B (not shown), to switch the calling line clear of the register and release the latter. When the wanted outlet is free and the group-selector switches through, a final selector relay FA operates and at fa4 removes negative battery from the d lead, releasing PTA, PTB, TA and finally SR. Local call; final selector operation. The final selector drive circuit is completed at sr2, ta1, and fa2. The operation of TA operated the first relay A in a counting-chain (Fig. 4, not shown), and the release of TA operates the next chain relay B which at b2 (Fig. 9) disconnects SR. Relay A also steps on the reading distributer by firing TCDB (Fig. 7B), so that the second or tens digit phase is now connected to the detector transformer TP by the revised setting of the marking relays MA ... ME. On the final selector the outlets are arranged as shown in Fig. 8A. Each group of ten begins with the same unit digit as its tens digit, and the remainder of the unit digits follow in order, e.g. as shown for the forty group in Fig. 8B, where multiple outlets are also shown for some subscribers. In this way the phase marking denoting the tens group is used also as a units phase marking, and the use of two phases on one contact is avoided. The final selector drives until it finds the correct phase as before but does not test for busy condition at this stage, and PTA operates over b3 up immediately WP detects the correct phase. When PTB and then TA operates, operating chain relay C, the latter triggers TCDC (Fig. 7B) and the units digit is set up on the marking relays. The selector is thus released and drives until it finds the new phase marking required or reaches a positive potential on the contact following the group tested, when the signal " OCC " is returned to the calling subscriber as before. When the correct outlet is found SR operates over d2 up, br1, ptb1 up, and removes earth from the a-SA lead, relay FB (Fig. 3B) operating to switch the call through at fb1, fb2. At fb5 a check relay CK is operated and at ck3 and ck4 removes the battery and phase markings from the selector banks. Local call; check for correct connection. When the final selection is made relay TA (Fig. 9) operates after the tens digit search and in turn operates a chain relay E, Fig. 4A (not shown), which fires the distributer tube TCDA again (Fig. 7B) and connects the called line to the WRU section of the code generator. This causes the called station to return its directory code designation both to the calling station and to the register, where it is sequentially applied to the storage tubes SXA ... MZE in the usual way. If this signal agrees with that already stored on these tubes no change in their condition occurs, and the tube CCA finally operates relay CC which is utilized to switch through the connection. If however there is a discrepancy between the code received and that stored, at least one of the pairs of tubes will reverse its condition and the resulting cathode pulse is utilized to operate a relay WC, Fig. 5A (not shown), which connects the calling line to the code generator which returns a WC signal to indicate a wrong connection. Junction call; transmission of wanted station designation. The storage relays MA ... ME are operated as before to connect the wanted phase to the detector transformer TP and as the first digit is arranged to designate a junction call they also operate a junction relay JR, Fig. 4 (not shown). The group selector is driven to find a free outlet, when TA (Fig. 9) operates as before to the correct phase and chain relay A follows, firing TCDA (Fig. 7B) and operating relays to connect the time-base start circuit to the mark contact of TRB over a contact of the junction relay and also to condition the storage tubes for transmission. When a junction is claimed a space is returned until a distant register is seized when the consequent marking condition at TRB starts the time-base and the conditions of the cathodes of tubes SXA ... MXE are applied sequentially to a transmitting trigger TRS, TRM (Fig. 7C), controlling a re-transmitting relay. At the end of the first digit TCDB is fired and the second digit sent on. The third digit is similarly transmitted and at the end TBCA (Fig. 7B) fires and operates relays BCA ... BCC to reverse the connections to the transmitting trigger TRS, TRM, so that as the time-base continues to operate the stored digits are sent on in their complemental form, i.e. marks become spaces and vice versa. The start and stop elements are not affected and are still transmitted as S and M respectively from the distributer tubes UDA and UDG. After the three digits have been repeated TBCZ fires, quenching TBCA and releasing BCA ... BCC of which BCC is arranged to stop the time-base, release the register, and switch through the connection at swb1 ... swb4 (Fig. 3A). Junction call; message storage. If all junction outlets are busy search continues for a free storage unit, which is of the magnetic recording type described in Specification 685,032, and is connected to the group selector. If a free unit is found the battery on level f (Fig. 10), operates a relay to transmit a storage signal ST to the calling party. Over arc e a relay SA operates to'start the storage unit motor and sends back a mark over the b wire which operates TRB to M and starts the timebase to transfer the stored code and its binary equivalent to the storage unit. When the transfer is completed the register releases as before and