Patent GB-836557-A (GB)
Title: Improvements in or relating to automatic telephone systems
Inventor: BAKER GEORGE THOMAS
IPC: H04Q3/00
Filed: 1955-07-11
Abstract: 836,557. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. July 11, 1956 [July 11, 1955], No. 20049/55. Class 40 (4). Connections are set up over automatic switches under the control of a magnetic drum register, information as to the identity of the calling and called parties being registered on the drum and the switches to be used for setting up the connection being determined under the control of the drum dependent on this information. A continuous record of the busy or idle condition of the various switches and outlets is made on the drum, this information being effective to determine which switches shall be used for setting up a connection. Use is made of crossbar switches with two additional levels over one or other of which a connection is extended so as to give a wiper-switching effect. The calling party may be connected through a secondary switch to either end of a transmission bridge. Determination of the position of the magnetic drum register corresponding to a dialled number is effected by comparing a registration of the dialled number with a waveform including all the various possible numbers, the waveform being related in phase and repetition frequency to the movement of the drum. If the called party is busy the dialled number is retained on the drum and repeated tests are made until he becomes free. If the calling party has hung up in the meantime he is rung when the connection is completed. Trunking. A 200-line system employs 5 primary cross-bar switches P1-P5 and 5 secondary switches S1-S5 with 20 transmission bridges arranged in pairs such as TB1, TB2 between each of bridges 3-10, the secondary switches, bridges 1 and 2 being reserved for outgoing junctions or access to operators. 2-Wire switching. Only the speech wires are switched so that the 8 pairs of contacts at each cross-point can deal with 4 subscribers, selection of the required pair being made over levels 11 and 12 in both the primary and secondary switches, as shown in Fig. 2. Operation of switches, Figs. 3-5. In the example a call is made from SUB2 to SUB 1 over primary switches P1, P5, secondary switches S1, S5 and transmission bridge TB8. The switches, links and transmission bridge are selected under the control of a magnetic drum which strikes tubes in series with magnets or relays according to the time point in a recurring series at which a pulse is sent. Three digits are dialled and recorded in the calling party's register on the drum. Tests are made by the drum equipment to find a suitable route. The selecting tubes are first struck in series with a high resistance and light only dimly. If then the called party is found to be idle a pulse PL6 fires tube STT, Fig. 5, to operate relay ST which applies low resistance battery to ignite the selecting tubes fully in series with the associated relays. Route determination starts with a transmission bridge, connection being made first to the called party and then to the calling party. A timed pulse fires TT8. Fig. 4, dimly to select transmission bridge TB8, operation of ST energizing H to operate B and prepare circuits for the SA and SB relays and appropriate bridge magnets in the appropriate secondary switches for both parties B energizes MS to start up the ringing and tone equipment. When the appropriate primary switch selecting tube CT5 has been struck relays 5PA and 5PB in the associated primary switch pull up to energize the select magnet PSM1- PSM10 corresponding to the lighted tube in the group ST1-ST10. Similarly magnet PSM11 or PSM12 operates under control of tube WT1 or WT2. Meanwhile 5SA and 5SB have operated to enable tube WT3 or WT4 to control secondary switch wiper selection by operating magnet SSM11 or SSM12. Also the first or second choice relay FC or SC has operated. Assuming FC has operated then first select magnet SSM1 in secondary switch S5 pulls up. Relay SS energizes over a circuit through the contacts of the select magnets of the primary and secondary switches, the bridge magnet PBM5 of the primary switch following. The bridge magnet SBM5 of the secondary switch then operates to extend the connection to the called ine. Relay SS applies battery to lead S1 to signal this connection to the drum control equipment which then performs a similar set of operations to connect the calling line to the chosen transmission bridge. Relay RD, AA, FA operate to complete the calling party's side of the speech circuit. Ringing current from lead RG, Fig. 5, is applied through FC to the called line, ringing tone through AA to the called line. When the called party replies FC pulls up to restore TP and MS, disconnects ringing current and tone, and switches through to the called party. During conversation the transmission bridge is marked busy to the drum control equipment over contacts b5. When either party hangs up AA or AC restores so that relay B falls back to release the connection. If the called party is busy when his line is tested or if all relevant links are busy the registrations are retained on the drum and repeated attempts are made to set up the call. The calling party may hang up and is then rung when the connection is established. If both parties leave their telephones ringing might continue indefinitely but this is prevented by a pulse appearing on lead S after a suitable interval to operate relay TP. TP connects up the Z pulse lead so that after a further interval of ringing tone a Z pulse operates AC and AA to energize FA and FC to end ringing. At the end of the Z pulse AA and AC fall back to restore B and release the connection. Magnetic drum. General arrangement. A magnetic drum of the type described in Specifications 717,687 and 776,772 has five register tracks each dealing with 40 subscribers. The different subscribers' registers in each track are defined by waveforms TA1-TA4 and TB1- TB10, waveforms TW1-TW5 connecting up the register tracks in turn. The usual address track is replaced by a rectifier matrix which supplies waveforms corresponding to each of the 200 subscribers. Each transmission bridge register and each summation track are twice as long as a subscriber's register. Each transmission bridge register indicates whether the related bridge is busy or idle, and if busy which links it is connected to. The summation track registers link busy information. All incoming pulses are stored temporarily in the same position of a register by electronic relay MAN, Fig. 6, and subsequently transferred to the particular position they are to occupy in the manner described in Specification 717,687 by electronic relays MAB-MCB. Generation of the control pulses for setting up the connection is determined by electronic relays MAC-MGC and MAD-MDD. Route selection is controlled by MAE-MFE, MAF-MEF and MAG-MDG. Magnetic drum. Detailed operation. In known manner a dialled impulse marks the register temporarily at TX4, TY6 over circuit 5, an additional mark at TX5, TY6 being produced if a further impulse arrives before the first is transferred. The impulse or impulses are then transfered by MAB and MBB to the appropriate digit register blocks TY2-TY4. The interdigital pause operates MCB which busies each digit register. If the transfer track is clear MAC then operates and over gate 37 inserts a " hunt for address " mark at TX5, TY1 on the transfer track. MAC also operates MBC which transfers the registered digits to the transfer track in the usual manner over gates 39, 40. Staticizers. MBC also sets the staticizers, namely electronic relays MAS-MCS and MDSMFS, Fig. 12, for the calling and called subscribers, respectively. According to which of the five register tracks is being scanned gates 41-43 set up one or two of MAS, MBS, MCS. The called subscriber's staticizer is set up by reference to the second dialled digit so that MDS operates for digits 1 and 6, MES for 2 and 7, MDS and MES for 3 and 8, MFS for 4 and 9, MDS and MFS for 5 and 0. The outputs from the two staticizers are combined with the different TX waveforms in gates 59-63 and 64-68, Fig. 13, to produce outputs SZA, SZD corresponding to the calling and called primary switches. The outputs from the staticizers are also combined with the different TB pulses in gates 69, 70 to produce two pulses PL2. The staticizer relating to the called line produces the first pulse and is then reset by gate 71 after MBD, Fig. 8, has operated as described later. Release of the called staticizer enables the calling staticizer to produce the second pulse PL2, MCD, Fig. 8, then operates to restore the calling staticizer. Summation track. Electronic relay MBC which, as already described, transfers the digits and sets the staticizers also operates gate 73 to enter a mark at TX2, TY6 on the transfer track to initiate filling of the summation track to indicate which of the various links are busy. The different links joining primary and secondary switches are allocated different combinations of waveforms TX1-TX5, TY1-TY6, TA1- TA4. The mark at TX2, TY6 operates MDG which restores after two TA pulses. MDG operates in turn for all the various transmission registers to enter the condition of the associated links into the summation track through gate 76, Fig. 11. This information is entered repeatedly until the mark at TX2, TY6 is removed at completion of the connection when MDG restores to clear the summation track. Hunt for called subscriber's register. The " hunt for address " mark, previously described, operates MCC, Fig. 7, to start a hunt for the called subscriber's register by comparing the digits registered on the transfer track with the address waveform SLAD. MCC is continually reset by gates 79, 80 until correspondence is found when it enters a " called subscriber found " mark at TX1, TY5 on the transfer track over circuit 81. If the called subscriber is busy the auxiliary head enters a busy mark on the transfer track over gate 82 and restores MCC over gate 83. If the called sub