915,972. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. March 31, 1960 [March 7, 1959], No. 7969/59. Class 40 (4). A telephone exchange has a first group of registers LRG of which one is taken into use for a call originated within the exchange and, if the call is to an exchange in a different area, a controller EC common to all registers is seized and given the digital information indicative of the wanted exchange whereupon the controller seizes one of a second group of registers ORG to which it transfers the exchange digits, the second register receiving the remaining digits from the calling subscriber after which the controller is seized for a second time to set up a path to an outgoing junction over which the second register transmits the necessary digital information. The arrangement is employed in an exchange network where subscribers dial trunk calls and makes use of high-speed registers, senders and common control equipment. Locally originated calls.-Subscribers line circuits SLC are arranged in groups of 100 lines, 20 such groups being under the control of a 2,000 line controller GCC which at the rate of 400/sec. scans each group of 100 simultaneously. Scanning halts when a calling condition is found and the calling group is identified. An originating controller OCC, common to all controllers GCC, is seized and marks all originating relay sets ORS accessible to the calling line. One such relay set ORS is seized along with a local register LRG. In the drawings cross-bar switches are shown as uniselectors, the wipers representing hold bars and the bank contacts representing select bars. The linefinder/final selector LF/FS, comprised of primary and secondary switches PR1, SEC, as described in Specification 813,338, connects the calling line to the relay set ORS supervised by controller OCC; OCC and GCC releasing while the switch magnets operate so that scanning of the 2,000 line group is resumed. Dial tone is sent from ORS and the dialled digits are registered in LRG. Locally terminated call.-When the full complement of digits is registered in LRG application is made to an exchange controller EC, common to the whole exchange, which takes over the dialled information in parallel mode. Controller GCC is now re-enlisted and marks the wanted line which, if free, marks all available paths over LF/FS while the relay set ORS marks all available paths from itself over selector stages 1SL, 2SL, 3SL; the inlets of each such stage having access to all outlets. One of the free paths marked backwards from the called line is seized, thereby determining a particular selector 3SL which is also seized. Controller EC now sets up a path over selectors 1SL, 2SL, and ensures that only ore of the possible selectors 2SL is used. While the select magnets of the path are operated controllers EC and GCC retire, hold magnets operating under control of local register LRG which tests the connection and releases. Ringing is effected from a local relay set LRS. Should the called line have been busy GCC signals EC which signals LRG to set up ORS which sends busy tone. Locally originated call to exchange within the local area.-Two-wire junctions OJ2 serve the local exchange area and digits indicating such a call cause controller EC to mark all free junctions OJ2 in the wanted direction. Large numbers of junction groups are accessible over selectors 3S02 and relay set ORS marks all paths accessible to it over selectors 1SL, 2SL, and if necessary 3S02, a junction marked from both EC and ORS being seized. A calling loop may be extended forward to the wanted exchange from ORS but if special signals are required, ORS is switched out of circuit by EC and calling is effected from relay sets JRSA, JRSB at the junctions. Incoming call originated within the local exchange area.-Such a call appears on a twowire junction IJ2 and seizes a relay set IRS taking into use a register IRG over a connector IRC which may be as described in Specification 915,971. Digits from the calling exchange pass over a fast acting by-path round IRC until this operates. A second dial tone may, however, be sent when IRC has operated. Register IRG works in conjunction with controller EC in the same manner as does LRG for a locally originated call. Outgoing call to exchange outside the local area.-Such calls are set up to four-wire junctions OJ4 accessible to locally originated calls over selectors 1SL, or to incoming local area calls over selectors ISL, and the stages 2SL, 3S04 and OTS. On recognition of a trunk prefix and exchange code, register LRG, or IRG, transmits the information to controller EC which selects a 2-wire to 4-wire relay set 2/4RS and passes control to a register ORG associated over connector ORC. Controller EC and register LRG or IRG release but EC is taken into use again when further digits are received to provide metering information to relay set 2/4RS and to seize an outgoing junction relay set 4RSB. Call incoming from outside the exchange area.- Such a call is made over a 4-wire line to a junction such as IJ4 from which relay set 4RSI takes a register TRG into use over connector TRC. Signalling over the trunk is done at high speed, TRG sending a " start send " voice frequency signal back over the junction calling for the first routing digit which comprises two consecutive bursts of voice frequency in a two-out-of-five code. Two of five tuned circuits in TRG respond and if, on checking, the code is acceptable an " acknowledge " signal is sent. If the code is unacceptable the " start send " signal is repeated and the first digit is sent again. If the code is still unacceptable " start send " is again sent and the calling exchange connects busy tone to clear the call. In response to " acknowledge " signals further digits are similarly transmitted. If the trunk call is locally terminated all the digits are received before EC is consulted and the wanted line is tested over GCC. A path is marked forward from 4RSI over TS, 4-wire to 2-wire relay set 4/2RS, and 2SL. From the wanted line a path is marked backwards over LF/FS to a selector 3SL. If the trunk call is in transit to an exchange within the local area, digits are retransmitted by register TRG under controller EC which seizes a junction OJ2. These digits are sent at 10 impulses a second and retransmission may begin before TRG has received its full complement of digits. If the trunk call is in transit to a further 4-wire junction to an exchange outside the local area controller EC sets up a connection over TS and OTS to a relay set 4RSB associated with a 4-wire junction such as OJ4. Controller EC and register TRG release without use of " acknowledge " or " finish " signals which are supplied by the wanted main exchange at the end of the tandem connection. Specification 915,793 also is referred to.