Patent GB-814944-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
Inventor: HOPLEY HORACE EDWARD
IPC: H04Q3/00
Filed: 1955-10-29
Abstract: 814,944. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Oct. 29, 1955, No. 31003/55. Class 40 (4). In an automatic exchange system each group of subscribers' lines is served by a switching arrangement comprising one primary and one secondary cross-bar switch which serves to extend, under the control of a marker individual to the group, a calling line to a transmission relay set accessible to all groups. The switching arrangement also serves to extend a transmission relay set to a called subscriber, control being then effected jointly by the relevant marker and one of a plurality of control circuits common to all the groups. Trunking lay-out, Figs. 1, 2. Each group of 20 subscribers is served by a primary switch such as SAA, a secondary switch SBA and a marker such as MKR1. Any one of ten transmission relay sets or feed-bridge circuits TRS1 ... 10 may be used on a call and the services of any one of three control circuits CC1 ... 3 may be called in. A calling subscriber obtains access to one of four originating links LK1 ... LK4 over primary switch SAA, the position of the calling subscriber being determined by the operation of one out of ten select magnets 1SM ... OSM and the operation of one out of two auxiliary select magnets 1AM, 2AM, the connection being held by a bridge magnet associated with the link. The link terminates in a bridge on the left-hand side of the secondary switch SBA from which access is available to the originating sides OT1 ... OT10 of the transmission relay sets TRS1 ... TRS10. The trunks OT1 ... OT10 are multipled over the left-hand sides of all the switches SBA ... SBE serving the respective 20 line groups. A control circuit say CC1 and a transmission relays set say TRS1 are selected by an allotter and the calling subscriber connected via TRS1 to CC1. When the latter has received the dialled digits it seizes a marker appropriate to the wanted 20 line group and causes the latter to effect connection from the terminating trunk TT1 of the transmission relay set TRS1 to the wanted subscriber via the right-hand side of a secondary switch and a terminating link such as TR5...TR8. The allotter contains chain circuits which cyclically vary the order of priority for seizure of both the link circuits and the control circuits. It is also arranged to vary the order of priority of the first three transmission relay sets, but if these are all in use the priority of the remaining ones remains invariable. The layout is such that additional primary-secondary switch pairs, transmission relay sets, markers and control circuits may be added as desired to increase the capacity of the exchange from an original 20 lines in stages up to the 100 line capacity of the system described. Non-numerical switching. At any given time a relay DK and a relay LK will be operated by the allotter to preselect respectively an associated control circuit say CC1 and an associated transmission relay set (say TRS1). Relays DR are normally operated in all markers. In the chain AA, AL; BA, BL; C, CL which allots priority to one of the transmission relay sets TRS1 ... TRS3, relays AA, AL are assumed operated to allot priority to TRS1. When the calling subscriber completes his loop line relay LS operates followed by one of relays GA, GB (say GA) in the marker according as the calling line is in the first or second ten-line group of its twenty line group. Relay GA earths lead BMA to bring up relay DT in the other markers which are thereby disabled. Relay GA also earths VS to start the ringing current and tone generator. Relay GA brings up AB followed by ABA. Relay AB brings up select magnet 1SM of primary switch SAA (determined by the operated LS relay) and also operates BA in the cyclic allotting chain for TRS1 ... TRS3. Relay ABA brings up A in the transmission relay set TRS1 (allotted by LK) and SA follows to connect the latter to the control circuit CC1. Relay ABA in conjunction with GA brings up the auxiliary select magnet 1AM of the primary switch SAA and the secondary switch select magnet 1SM of SBA corresponding to the transmission set TRS1 follows. Magnet 1AM operates relay RA of the preference chain. RA ... RD corresponding to the first idle link LK1 and the corresponding relay DA operates to bring up the bridge magnets 1BM (SAA and SBA) at each end of the link. Connection between the calling subscriber and TRS1 is thus established, the cut-off relay K in the subscriber's line circuit being operated over the bridge j. Relay A has meantime operated hold relay B and E follows. In the control circuit BB and TA operate followed by PA which connects up dial tone. In the marker DR shortcircuited by AB and ABA release slowly whereupon the marker is released. A short-circuit is thereby removed from BL in the allotter thereby shifting the point of entry in the preference chains for TRS1 ... TRS3 and CC1 ... CC3 to operate LK, DK in the thus newly pre-allotted circuits, in preparation for the next call. Reception of digits. These are received on chain PA ... PF in conjunction with CX, PA being already operated over its centre winding. On the first impulse break the release of A operates PB over its right-hand winding in series with the left-hand winding of PA. Relays CD, CE also operate and stay up for the remainder of the impulse train. PB transfers the holding earth from the centre winding of PA to the centre winding of PB. When A reoperates the right-hand winding of PA is disconnected and the latter releases. Subsequent impulses step the operated condition along the chain, relay CX also coming up on the sixth impulse whereupon the chain starts stepping again from PA onwards. It is assumed that the first digit is 2 so that PC remains operated. In the control circuit, Fig. 10, terminals TBA are strapped to corresponding terminals TBB if the corresponding first digit is used and the relays PA .... PE, CX cause the operation of one of relays DAA ... DEA corresponding to the wanted twenty-line group and also the operation of relay CO if the wanted line is in the last ten of its twenty line group. In this case DAA and CO are operated, when CD falls back at the end of the train. Relay DAA operates FD which releases the counting relay PC and when CE falls back PA is reoperated and the counting chain thus zeroized. The second digit is then similarly registered. Assuming this digit is 0, PE and CX remain operated. Relays CD, CE operate at the beginning of the train and bring up SD. Completion of connection to called party. When CD, CE release after the second digit relays T, TR, SZ operate in the marker indicated by DAA. These may only operate if the SZ relays in other markers are back and provided DT is back, i.e. no other marker is engaged in an originating call. Relay SZ brings up auxiliary magnet 2AM (indicated by CO). Relay TR operates the primary select magnet 0SM (SAA) indicated by CX and PE. Magnet 2AM brings up the secondary select magnet 1SM(SBA) corresponding to TRS1 and indicated by SA. Other calls may meanwhile have shifted the entry point of the RA ... RD link allotting chain several times. It will be assumed that RA (now corresponding to terminating link number 5) again has priority and that the corresponding link is idle. Magnet 2AM then operates RA and DA follows to bring up the primary and secondary bridge magnets 5BM (SAA), 5BM (SBA) to complete the connection from TRS1 to the called subscribers line circuit. Relay TC operates slowly-over bridge k and releases SA which releases the control circuit and the marker. For an ordinary subscriber terminal PN is connected to the P-wire. If the line is idle H and K operate over this wire and when E subsequently releases ringing current and tone are connected up. When the called party answers ring trip relay F operates in the usual manner and back bridge relay D follows. Release is controlled by the calling party. If the called line is busy H fails to operate and when TC operates and E releases busy tone is returned in the usual manner. The relay set TRS1 contains a network Rll, C3 which remains across the line during the setting up of the call as a balancing network in case the caller has a loud-speaking telephone. Privileged intrusion on busy lines. Such a privileged subscriber has his terminal D connected to E (earth). When a call is made to a busy subscriber and H fails to operate TC operates as usual and connects the abovementioned earth to relay D which operates, brings up F and holds E. The caller is now connected into the existing conversation. When the conversing parties hang up, as requested, H now operates in series with the wanted party's K relay and releases D. Relays E and F release and ringing current is then transmitted in the usual way and the call proceeds normally. Inter - exchange tie - lines. Ordinary subscribers' line circuits are used for terminating tie-lines, terminal PN being connected to the P-wire and in addition battery is connected to terminal MN. A call incoming from a distant exchange over such a tie-line is dealt with as for a local subscriber's call. In the case of a call outgoing to a distant exchange connection to the tie-line is established as to an ordinary subscriber, but during the slow release of E, the battery on lead MN brings up relay TL and F follows. Relay TL loops relay D across the line to provide a seizing and holding signal for the distant exchange, and unmasks impulsing contact a2 for repeating the impulses to the next exchange. During subsequent dialling E operates to provide a clean impulsing loop. P.B.X.-type hunting over a group of tie-lines. Any tie-line of a group must have 0 for its units digit. In addition the tens digit must be odd for the first line of the group and even for the remaining lines of the group. The PN terminal of the first line of a group is strapped to one of the terminals EL1, EL3, EL5 and the PN terminals of all the