Patent GB-804041-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: BAKER GEORGE THOMAS
IPC: H04Q3/42
Filed: 1955-06-07
Abstract: 804,041. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. May 22, 1956 [June 7, 1955], No. 16371/55. Class 40 (4). A telephone system employs registers of the closed circulating type for controlling the setting up of connections of automatic switches, the registration of a wanted number in a portion of the register device allocated to the calling party being retained until the calling party hangs up after connection has been made to the wanted line or until the calling party makes a new call. The description and drawings are identical with those of Specification 804,042 but the claims differ. The invention is described with reference to an 80-line exchange in which the registers of the magnetic drum type are shown in Figs. 4-6 and control cross-bar switches shown in Figs. 1-3. Cross-bar switches. An allotter circuit comprises a ring of hunt tubes HT1-HT10, Fig. 3, and associated seize tubes ST1-ST10 together with a drive tube DT. The hunt tube, say HT1, corresponding to a preselected transmission bridge is conducting and the associated seize tube ST1 is struck when the common equipment is associated with that bridge to control the setting up of a connection. On operation of one or other of the two cross-bar line finders, earth appears on lead BY and combines with the cathode potential of the conducting tube HT1 to prime drive tube DT which fires to the next DP pulse. The discharge therefore moves to the next tube HT2 and if the associated bridge is already busy as indicated by earth on lead BY a further pulse is obtained from tube DT and the discharge moves on until a free bridge is located for the next connection. Pulses from drive tube DT are also fed to a toggle circuit PT1, PT2 so that lead PU is marked negative or positive, respectively, according to whether hunting is of is not taking place. In response to an initiating pulse from the drum control equipment over lead MBD, described later, the appropriate seize tube, say ST1, is struck so that relay H, Fig. 1, pulls up. Relay H connects the common control leads to the selected transmission bridge and energizes relay FA. Final selector. The initiating pulse on lead MBD has a time significance relating to the called number and fires one or more of tubes WAT, WBT, ABT controlled by binary counters S1-S3, as described in Specification 746,942, so as to operate one or more of the corresponding relays WA, WB, AB. The initiating pulse also operates the appropriate select magnets, e.g. SMFA(10) and SMFB(10), Fig. 2, of the A and B final selectors under the control of ring counter C. The associated off-normal contacts are closed to operate relay ST which closes a high-resistance circuit through the bridge magnet, say BMFA, Fig. 1, of the operative final selector, as determined by relay AB, and the two windings of relay BR, Fig. 3, only BR operating at the present time. Relay SM then pulls up to extinguish those tubes WAT, WBT, ABT which are conducting, and shunts the highresistance winding of BR to allow the bridge magnet to energize. The selected cross-point then closes and BR and the select magnets and associated tubes restore to normal. Relays ST and SM fall back, the latter slowly to allow B and CO to operate. B connects ringing tone to relay A. B and CO change over the circuit connections from final selectors to line finders. Line finder. A second impulse on lead MBD with a time significance relating to the calling number operates one or more of tubes WAT, WBT, ABT and the related relays and the appropriate select tubes and select magnets of Fig. 2, e.g. SMLA(1) and SMLB(1). As before, ST, BR, SM energize, this time followed by the bridge magnet, say BMLB, of the appropriate line finder as determined by relay AB. BR, the select magnets, and ST restore and lead BY is earthed to step the allotter. Before ST falls back CR pulls up. Operation of the bridge magnet switches the calling line through to relay A. If the calling subscriber is still on the line relay A operates to shunt CO, so releasing CR slowly. Before it falls back CR extinguishes seize tube ST1 and restores H to disconnect the common equipment from the selected bridge. Release of CR restores SM. The called subscriber is rung through relay FD and ringing tone is returned to the calling subscriber through relay A. When the called subscriber answers FD pulls up, switches through the speaking leads and disconnects ringing tone. Relay D then energizes. When either party hangs up release of A or D restores B which releases the connection. Called line busy. If the called line is busy a special mark is entered on the magnetic drum, as described later, the preselected bridge is not seized and ringing tone is not returned to the calling subscriber. The calling subscriber hangs up but, subject to the requirements of other subscribers for the transfer track, repeated tests of the wanted line are made. When the line becomes free the connection is set up as before except that as the calling party is not now on the line there is no circuit for relay A when the line finder switches through. Operation of CR restores FA. Release of FA shunts CO to release the common equipment. Ringing current is then applied to the calling line through FA and ring- ing tone to the called line. When the calling. subscriber answers FA reoperates to complete the connection. Magnetic drum, Figs. 4-6. The drum has two register tracks each catering for 40 subscribers, an address track' permanently recorded with the numbers of the 80 subscribers and a transfer track on which a called number is registered repeatedly all round the drum. The drum is of the type described in Specification 717,689. Registration of called number. As long as the subscriber's loop remains open electronic relay MN is operated and immediately reset by circuits 16, 14 as the related portion of the register track passes the writing and reading heads. When the loop closes coincidence circuit 11 enters a mark at TX1, TY4 and MN is operated by circuit 12 to enter a mark at TX4, TY4 over circuit 13. When the loop is broken again this mark is cancelled by circuit 15. When a dialled impulse is received so that the loop changes from closed to open circuit 17 enters a mark at TX5, TY4. When this mark is detected by an auxiliary head relay MAA is operated by circuit 18. MAA clears the timing count in block TY1 and the " closed to open " mark is cancelled by circuit 20. 1 is then added to the first block encountered in which there is no busy mark in the first element. For the first impulse of the first digit this block is TY2 and relay, MAB is operated over circuit 21, MAA being restored at the same time by circuit 22. Addition is made by the usual method of reversing registrations until a 0 is changed to 1 under control of circuits 23, 24 after which MAB is restored by circuit 25. At the next scan circuit 26 reoperates MAB to add 1 to the timing block and circuit 27 enters a busy mark at TX5, TY1. A timing count is. added at each scan until the next impulse occurs when 1 is added to the digit block in the manner already described,. the timing block being cleared again. At the end of the digit the timing block TY1 fills up and MAB remains operated to set up MAA over circuit 28. With MAA and MAB both operated the second digit is entered in block TY3. At the end of the digit a " dialling complete " mark is entered in this block so that MBA is operated by circuit 33 provided the transfer track is not already in use. MBA is reset if transfer is not permissible for any reason. If, however, MBA remains operated circuit 37 enters a " transfer " mark at TX1, TY1 of the register track, circuit 38 operating MBB in the same scan. Transfer of digits to transfer track. The dialled digits in the register track are then repeatedly registered at 4-block intervals round the transfer track by circuits 39 and 40. When transfer is complete MBC operates. Detection of called line. Comparison is then made between the digits set up oh the transfer track and those permanently registered on the address track. As long as there is discrepancy MBC is repeatecfly reset by one of circuits 42, 43 but when correspondence is found MBC enters marks in the first three elements of TY4 of the called subscriber's portion of the register track over circuits 44, 47 and 48 denoting " busy," "call connected " and " ring back control." MBH operates at the same time to enter a " called subscriber found " mark on the transfer track over circuit 46. If the wanted line is idle circuit 51 enters a mark at TX3, TY4 of the transfer track so that MBC remains operated until TX1, TY1 and operates MBD which pulses lead MBD to operate the final selector as already described. MBD is reset by circuit 53. When the final selector operates MBE operates to enter a " ready for line finder pulse " mark on the transfer track over circuit 55. MBE is normally reset at the beginning of each subscriber's portion of the track but when the calling subscriber's portion is scanned MBE remains operated to operate MBF. Circuit 58 meanwhile erases the " transfer " mark. MBF enters a " call connected " mark on the register track over circuit 60, and circuit 61 re-operates MBD which pulses lead MBD to operate the line finder as already described. At the same time circuit 62 enters a " finder pulse sent " mark on the transfer track. When the connection has been established circuit 63 operates MBG to clear the transfer track after which MBG restores. When the called party replies the normal release of MAC by circuit 72 is cancelled and MAC deletes information in the calling party's portion of the register track, MAD operating over circuit 73 to retain the " call connected " mark at TX2, TY4. The called number remains registered on the calling party's portion of the track until the calling party hangs up after a successful call when MAC is operated by circuit 67 and opens gate 68. Called line busy. If when the ca