Patent GB-779235-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: PEARCE JAMES GORDON
IPC: H04Q3/00
Filed: 1954-04-15
Abstract: 779,235. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. April 5, 1955 [April 15, 1954], No. 11138/54. Class 40 (4). In an automatic exchange the line finder/final selector stage consists of a number of switching units each having two primary and one secondary cross-bar switches arranged for link working and gives access to trunk relay sets each having access to at least one register, there being provided first means which upon origination of a call marks all idle trunks accessible to the caller, and second means which marks all idle relay sets having access to an idle register, the coincidence of tho two markings causing a further marking to be extended to a corresponding position in a high-speed hunting circuit which hunts for the first such further marking, thereby selecting the relay set to which the caller is to be connected. General lay-out of system. The exchange described employs 12 Î 10 cross-bar switches connected for double-group working, so that each serves 200 outlets, or, with internal multipling between bridges, 20 outlets. The linefinder/final selector stage (LF/FS) is represented by a switching unit consisting of two primary switches PSAA and PSBA (Fig. 1), and one secondary switch SSA, and the group selector stages by switches 1GS, 2GS, and 3GS, respectively (Figs. 5, 6). The bridges of the crossbar switches are shown as thick vertical lines, the bisected circle at the top of which indicates that they are arranged for double-group working. The subscribers are arranged in 400-line groups, each group being served by a line finder/final selector arrangement consisting of a plurality of (e.g. eight) switching units similar to that shown in Fig. 1. Twenty subscribers' lines are terminated on each bridge in the two primary switches of a switching unit and are multipled to corresponding positions in the other pairs of primary switches of the LF/FS arrangement. Originating trunks ORIG for use on calls outgoing from the 400- line group extend from five bridges in each secondary switch via a grading frame GFA to separate calling trunk relay sets, e.g. ATRS1, ATRS2; and terminating trunks TERM from outlets of third group selectors extend via the grading field GFD (Fig. 7), to the remaining secondary switch bridges. Five LF/FS arrangements serving 2000 lines are associated with one control equipment CE(LF/FS), and the exchange has a single originating controller OC incorporating a five-way allotter making it accessible from each CE(LF/FS) one at a time. Each relay set such as ATRS1 includes the calling side of a transmission bridge and tone and supervisory arrangements, and has access via simple register connectors to two registers (R1A, R1B) of a common pool of registers. The single exchange controller EC (Fig. 5) may be taken into use by any register exclusively when all the information necessary for setting up a connection has been stored by that register. The calling trunk relay sets terminate on individual bridges of the first group selectors, the outlets of which are connected via grading field GFB to the bridges of the second group selectors. The second group selector outlets may be divided between outgoing junctions and local trunks in accordance with traffic requirements. The local outlets are graded by field GFC to trunks leading to third group selectors, each trunk including a called trunk relay set BTRS incorporating the called side of a transmission bridge and supervisory and ringing equipment. In the case of an exchange comprising twenty 400-line groups of subscribers or less, each third group selector, having twenty outlets, can provide access to each of the groups, but in the 10,000-line exchange under consideration the third group selectors 3GS are divided into five groups and are connected to the twenty-five LF/FS arrangements in the manner shown in Fig. 9. Operation. The gas-filled cold cathode tubes used for control purposes are represented in the drawings by circles, and the conditions applied to them by the following symbols: (a) bias potential by a filled-in arrow-head, (b) triggering potential, or pulse which is ineffective unless accompanied by a bias potential, by an open arrow-head, and (c) firing potential, which is effective to fire a tube, by two open arrow-heads. The control equipment CE(LF/FS) serving five LF/FS arrangements includes circuits for scanning the 2,000 line circuits served and for this purpose the latter are divided into 100-line blocks so that a 10 x 10 co-ordinate scanning circuit consisting of two rings of cold-cathode tubes may be used. The twenty 100-line blocks are scanned simultaneously, and when a call is initiated over a line the scan proceeds until a position corresponding to that line, and to nineteen other lines in other 100-line blocks, is encountered. A twenty-way electronic highspeed hunting circuit then advances to a point corresponding to the 100-line block containing the calling line, the coincidence of the calling line condition and the stopped positions of the scanning and hunting circuits causing the line tube LT in the line circuit SLC of the calling line to fire, thus busying SLC. Firing of LT fires the line mark tube LMT, and the potential derived therefrom is extended via isolating rectifiers MRA, MRB to points X and Y in a 20 X 20 co-ordinate marking field. Point X is connected to twenty-line circuits terminated at corresponding positions in the same horizontal ordinate of each pair of primary switches in the LF/FS, and point Y to. twenty-line circuits terminating on the same primary bridge. The potential applied to X primes eight tubes such as PSCT each associated with a select magnet PSM and an auxiliary magnet PAM corresponding to the horizontal ordinate position of the line circuit in a pair of primary switches; and that applied to Y primes eight tubes such as SSCT each associated with a select magnet SSM and an auxiliary magnet SAM of one LF/FS secondary switch. The firing of the line mark tube LMT also fires an isolating tube LIT (via point Y) common to twenty subscribers served by one particular primary switch bridge in each switching unit of the LF/FS, and this extends a tube striking potential via point Z over closed contacts (PBMC) of the unoperated magnets of the appropriate primary switch bridges in each switching unit to link tubes (LKT), each of which corresponds to an idle primary/secondary link accessible to the calling subscriber. Each fired link tube applies a pulse to two groups of five leads extending to isolating tubes 1-OIT to 5-OIT and 1-TIT to 5-TIT, respectively, corresponding to the originating and terminating trunks accessible to that link. In the meantime, the originating controller OC will have been taken into use exclusively by the CE(LF/FS) and it applies a bias condition over lead BOI to all the originating isolating tubes of the exchange. Those tubes which also receive the link tube pulse are fired and priming potential is thus extended to the corresponding originating trunk tubes such as 1-OTT, provided that the relevant originating trunks are not already in use over the particular LF/FS (i.e. relevant contacts of 1SBMC to 5SBMC closed). The originating controller OC also transmits a pulse over path MR to all the registers in the exchange, each of which includes a tube RFT (Fig. 4) accessible from path MR via individual switching means (represented by contact IMC) when the register is idle. Tubes RFT are therefore fired in all idle registers. Each calling trunk relay set, e.g. ATRS1, has access to two registers (R1A, RIB) of the common pool of registers, access to which is provided by a pair of register connector relays (RC1A, RC1B) forming part of the relay set. The control circuit of each relay set also includes a mark-free tube, e.g. 1MFT, which is primed when the relay set is not in use. The firing of a tube RFT applies a bias to a plurality of changeover'circuits such as R1AT, R1BT (one for each originating trunk relay set having access to the register concerned), each of which is coupled to the relevant mark free tube such as 1MFT. The arrangement is such that if the " A " register of a pair is free the "A" tube of . the changeover circuit is primed and the "B" tube is biased back; and if the "B" register is free it applies a priming potential to the " B " tube but this is effective only if the " A" register is busy. The controller OC includes a sequence control arrangement which now sends a pulse over lead MCO to all the changeover circuits in the exchange so that the firing of one of the tubes, e.g. R1AT or R1BT, of each circuit which is associated with a free register takes place. Each fired changeover tube primes the corresponding register connector relay operating tube, e.g. RC1AT and applies a pulse to the related mark-free tube, e.g. 1MFT, which will be primed if its relay set is idle. Thus, all trunk relay sets which are idle and have an idle register available to them are identified by a fired mark-free tube. Each such tube returns a pulse to a corresponding originating trunk tube such as 1-OTT; those tubes associated with trunks usable on the present call are already primed and each of them which receives a pulse will be fired. The firing of a tube such as 1-OTT causes the first tube of the associated pair of tubes such as 1MT and 1ST to be fired and the second to be primed. A high-speed hunting circuit HCA (Fig. 2) common to the whole exchange has forty stages each consisting of two tubes ST and HT, the input and output leads IP and OP of the stages being associated via strapping field SF with the forty pairs of tubes such as 1MT and 1ST. The firing of a tube such as 1MT causes a pulse to be applied to lead IP of the relevant hunting circuit stage to prime the seize tube ST and back-off the hunt tube HT. The sequence control arrangement now sends a pulse over the hunt start lead HS to the first stage SI of the hunter and if