Patent GB-674840-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: IRGIN CHRISTOPHER RONALD
IPC: H04M15/10
Filed: 1948-04-20
Abstract: 674,840. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. April 7, 1949 [April 20, 1948], No. 10831/48. Class 40 (iv). In an automatic exchange network in which calls between end exchanges are routed through sector switching centres and district switching centres, discriminating equipment at the sector switching centre determines the route and tariff and transfers the information to a time-zone metering equipment located in the speech path to control the setting of a junction hunter and to establish the appropriate metering circuits, the routing and numerical digits being received and stored by the discriminator on mechanical impulse regenerators and subsequently retransmitted when a free junction has been found. The discriminator is released immediately the called subscriber answers. Four dialled routing digits S, A, B and C are received by the local sector switching centre, the S and A digits in combination denoting the district switching centre required while the B and C digits identify the distant sector switching and end exchange respectively. Three separate tariffs X, Y and Z are assessed from the routing digits, each tariff consisting of a called party answering fee, a call duration fee, and, for the tariffs Y and Z, a setting-up fee which is recorded shortly after the called party replies. The time-zone metering equipment and the discriminating equipment are shown in Figs. 2 to 6 and Figs. 7 to 10, respectively. Calling line seizes discriminating equipment. A preparatory digit such as "0" is used for routing calls to subscribers outside the end exchange area over the first group selector and a three-wire junction a, b, c to a time zone metering equipment TZME in the sector switching centre. Relay C operates over wire c, starting a hunter switch F and operating a relay V which transfers the outgoing a wire to hunter wiper F4. When DF seizes an idle discriminating equipment DE, relays K and B operate in series over wiper F1, followed by relay KR which extends the incoming a wire to an impulse receiving relay A in the criminating equipment DE and busies it by operating relay TF over wiper F2. Simultaneous seizure of the DE by two TZME's is prevented by relay K which only operates momentarily due to reduction of current and thereby prevents relay KR from pulling up and disconnecting the drive. If all the DE's are busy, earth from lead 20 will be disconnected from contact 25 of wiper F2 so that the hunter seizes this position. A forced release relay FR will then operate over wiper F5, releasing all the operated relays except C and connecting busy tone from lead 10 to the a wire. Storage of routing and numerical digits for subsequent retransmission. Impulses representing the routing digits S, A, B and C followed by four numerical digits are repeated by relay A and stored on mechanical impulse regenerators MIRA, MIRB of the type described in Specification 458,095. Relays VA and VB operate for the duration of each impulse train and control the drive magnet DDM of switch DD which is stepped one contact at the completion of each impulse train. The impulses are directed over wiper DD4 to the receiving magnets ARM, BRM in the mechanical impulse regenerators, relay VA controlling the marking magnets AMM, BMM over wiper DD5. The first three impulse trains (representing the routing digits S, A, and B) are stored on MIRA, the next four digits (representing the routing digit C and three numericals) are stored on MIRB, and the last digit stored on MIRA, by which time MIRA will have re-transmitted some of its stored impulse trains. Further numerical digits up to a total of six may be stored, if required. In the regenerators, off-normal contacts na, nb are closed after receipt of the first impulse in the appropriate regenerator and remain closed until all the stored impulses are retransmitted, each complete impulse train being mechanically marked by a code pin acp, bcp, which is lifted when VA disconnects the marking magnet AMM or BMM. Registration of routing digits for route and tariff assessment. The S, A and B digits are also repeated over wiper DD2 and control respectively the positioning of a single-motion switch SD and the vertical and rotary positions of a two-motion switch AB which is of the type described in Specifications 391,151 and 450,019 and includes off-normal contacts n1-n3. At the conclusion of the A digit train the rotary magnet RM is energized over nl and wiper DD3 and steps the AB wipers to the first horizontal position in the level determined by the digit. Switch contacts NR1 are thereby closed to enable switch DD to move to position 3, the B digits then setting the switch AB to a final horizontal position. Distinguishing calls to be routed over district junctions. The S or the S and A digits are compared with those of the originating district. If the S digits differ, a marking earth is extended over wiper SD4 and a terminal group R7 in a route cross-connection field RCC to a district exchange junction terminal AD. If the S digits are the same the strap from the appropriate terminal R7 is omitted and the marking earth is then extended over one of the terminals in groups R1-R6 to terminal AD after the A digit has been received and the AB wipers have moved to the first horizontal position. Transferring route assessment to the TZME. Relay ST is pulled up by any marking earth extending across the RCC, and operates relay CS which energizes the drive magnets SM and DM of switches S and D located in the DE and TZME, respectively. The switches are driven in unison by interruption of relay CS until wiper S4 reaches a marked terminal. Relay FB then operates and terminates the drive by releasing ST. District junction seized. Wiper D3 applies an earth marking to terminal CD which is connected by jumpers to terminals 2 to 30 on levels HA1, HA5 of a junction finder HA. The operation of FB completes a circuit extending over hunter wiper F7 and wiper D2 to the junction finder drive magnet HAM which steps until an idle junction is found. Testing relay PJ then operates from battery on the outgoing c wire, pulls up relay RZ, disconnects the drive, and busies the junction. If all the district junctions are busy the HA wipers step to contact 50 and operate the forced release relay FR. Retransmission of stored digits. Operation of relay FB completes a circuit to magnet DOM of switch DO over wipers S3 and DO2 and the switch steps by self-interruption to position 3, completing an earth circuit over the impulsing contacts AIMP of regenerator MIRA in cooperation with relay RZ. RZ releases FB and operates relay BYA over wiper DO4. Relay IP temporarily energizes the transmitting magnet ATM until it is disabled by a slow-tooperate relay IS. The reset plunger ARP is thereby disengaged from a code-pin ACP and the impulse contacts AIMP operated in accordance with the stored S digit train. Relay IS falls back when the reset plunger engages another code-pin, followed by relay IR which is controlled by IS. Magnet DOM is momentarily energized between the release periods of IS and IR and steps switch DO to the next contact. The A and B digits stored on regenerator MIRA are transmitted over the outgoing a wire in like manner, relay IP re-operating in each case to initiate transmission of the next digit after relay IR falls back. After transmission of the B digit, wiper D04 transfers the regeneration control circuit to MIRB for transmission of the next four digits and finally returns the control circuit to MIRA for transmission of the last digit. Switch DO then moves to position 11 and relay IP falls back, followed by relay V which completes the speech path to the outgoing junction. The regenerated digits may be transmitted directly or converted at an outgoing relay set to voicefrequency signals. Tariff assessment. The tariff is determined by the S, A and B digits in combination (with the exception of special service calls) and is assessed from the positions of the wipers of switches SD and AB. Marking earth is extended over a horizontal level of switch AB to one of a group of terminals T1-T5 in a tariff cross-connection field TCC which are connected to tariff terminals AT, BT or CT according to the geographical tariff zone X, Y or Z relating to the digit combination. This assessment is transferred to the TZME when the C digit is received, wiper DD3 then completing an operating circuit for relay ST. The advanced wipers of switches D and S again move in unison until relay FB operates from marking earth extending over wiper S5, the wipers of D stopping on a contact 8-10. Called subscriber answers. Battery condition is returned over the outgoing a wire and operates relays P and L, followed by relay PR. The forced release relay FR is isolated and a drive circuit completed to switch M, which steps by self-interruption to contact 25. Slow-tooperate relay TA then pulls up over wiper M3 and by interaction with relay UA steps the M wipers to position 1, closing an operating circuit for relay LR. The delay between the operation of relays L and LR (about 100 ms.) prevents the called subscriber's answering fee from being charged if a transient condition occurs on wire a. Release of discriminating equipment. Relay PR releases relay B when the called subscriber answers and a homing circuit for the switches in the DE is completed from release alarm earth 20. The operated relays in the DE fall back as well as relays K and KR in the TZME. Relay KR releases relay TF and the DE is then isolated. Metering called subscriber's answering fee. Relay LR operates the appropriate tariff relay AT or BT or both, according to the tariff assessment X, Y or Z determined by the setting of wiper D2 on contact 8, 9 or 10, and steps switch M to position 2. Relays TA and UA interact to step switch M to position 3 and cause metering relay MT to operate momentarily so that the calling subscriber's meter is ope