1333791 Automatic exchange systems PLESSEY CO Ltd 28 April 1972 [8 May 1971] 13880/71 Heading H4K In an automatic exchange system wherein calling line identification (C.L.I.) information is required to be transmitted from a first to a second exchange, the first and second exchanges are connected by at least one multi-conductor line dedicated to the transmission of digit signals collectively constituting required C.L.I. information in respect of any subscriber's line circuit of the first exchange which is employed on a call over one of a group of junctions interconnecting the said two exchanges, there being provided at the second exchange means for applying demand signals to said one junction when employed on the said call and at the first exchange means for transmitting over one of the multi-conductor lines one appropriate C.L.I. digit signal of the required C.L.I. information for each of said demand signals. In particular each demand signal is in the form of a polarity reversal or the junction speech wires and the C.L.I. digit signal is transmitted between the exchanges by applying a D.C. potential to two out of four wires comprising the said multiconductor line; the C.L.I. information is then converted in the second exchange to 2 out of 6 multifrequency signals for transmission on to a third " transit trunk " exchange where the information is required for ticketting purposes, the demand signals sent to the first exchange being produced by the second exchange in response to multifrequency signals received back from the transit trunk exchange. General.-The arrangement includes a first exchange ES of the Strowger type which has access over junctions DJ and OJ to a second exchange which is of the 5005 self-steering crossbar type, and includes a distributer DIST and routers RTR and SSRTR. The junctions DJ are used for calls from a subscriber SUBA of the Strowger exchange to subscribers SUB locally connected to the cross-bar exchange whereas the junctions 'O'J are used for trunk calls from the Strowger exchange which are required to be connected through the cross-bar exchange to a transit trunk exchange (not shown). These latter junctions have associated therewith three four-wire lines 4A, 4B, 4C which each connect a respective outgoing C.L.I. repeater AOCR, BOCR, COCR at the Strowger exchange to a respective incoming C.L.I. repeater AICR, BICR, CICR at the cross-bar exchange. Associated with each outgoing repeater is a respective calling line identifier CLIA, CLIB, CLIC, and collectively associated with the repeaters are outgoing 'O' relay sets associated with the 'O'J junctions, the outgoing repeaters being allocated to a calling 'O'J junction according to a priority arrangement whereby, if idle, repeater AOCR is allocated in preference to repeater BOCR, repeater BOCR in preference to repeater COCR and repeater AOCR in preference to repeater COCK. The three identifiers work independently of each other thereby enabling C.L.I. information in respect of three different 'O'J junction calls to be simultaneously transmitted to the local/ transit cross-bar exchange. The provision of three C.L.I. links ensures that even when one link is busied out for maintenance purposes, there are two links remaining to meet security requirements. In order to facilitate a description of the transfer of C.L.I. information from the Strowger exchange to the transit/trunk exchange via the local/transit cross-bar exchange, the cross-bar exchange arrangement is first outlined. Local/transit cross-bar exchange.-This exchange has all the normal 5005 cross-bar svstem features and in addition is adapted to perform the transit function for exchanges such as ES. 500 subscriber lines are connected to a distributer DIST, of which there are 20 per exchange, via a respective line circuit SLC, the line circuits being accessible by a line marker LM and three calling line identifiers C.L.I. to C.L.I.3. The local subscribers use loop disconnect, i.e. decadic signalling techniques and calling subscribers are connected through to a local transmission relay group LTRG via an originating trunk OT, and thence to a local register LREG in known manner. The line circuits are arranged to identify themselves in respect of their functional category by a momentary signal presented by them to a register when a call is originated. Typical categories are ordinary, coin-box and priority subscribers, and operator and maintenance stations. Fourteen routers RTR are provided per exchange. The function of each is to complete connections between local subscribers, to connect local subscribers to outgoing junctions employing either decadic or m.f. signalling, to connect incoming calls from other exchanges to local subscribers or to outgoing decadic or m.f. junctions and to connect incoming 'O' calls from exchanges such as ES to outgoing m.f. junctions providing connection to the transit trunk exchange. In known manner each router is supplied with X and Y switching matrices to enable each router to carry out two connections simultaneously. Also if an attempt to set up a call over the X switches fails, a second attempt to complete the connection is made over the Y switches. Each router has direct access to a number of outgoing relay sets ORSXP, ORSYP, and has access via a secondary router SSRTR to further outgoing relay sets ORSXQ, ORSYQ which are common to all the routers. Router controls RCX, RCY are used to complete the relevant connections through the cross-bar switching matrices using known self-steering techniques which will not be further described. The routers differ from those of known 5005 systems in that incoming relay transmission groups RTRG and OTRG are provided which are connectible with incoming registers IREG. The OTRG relay groups are associated with the 'O'J junctions extending from exchanges such as ES employing decadic signalling techniques. As previously described these junctions are used only on 'O' junction calls requiring the transmission of C.L.I. information between the exchanges. The RTRG relay groups are connected via junctions MFJ or DJ with exchanges employing m.f. or decadic signalling respectively and are used for calls incoming to subscribers local to the cross-bar exchange, where C.L.I. information is not required to be transmitted. However all RTRG relay groups are substantially identical and are adapted to their particular working requirements, i.e. decadic or m.f., by the location of connections in an internal strapping field. Arrangement of registers.-Local registers LREG comprise first choice registers provided on the basis of one for each ten local relay groups LTRG and second-choice registers provided on the basis of one common to several sets of ten such relay groups. Each local relay group therefore has access in known manner to one first choice and one second choice register LREG. The incoming registers fall into three categories: some are for use only with incoming junctions using decadic signalling; others are for use only with incoming junctions using m.f. signalling; whilst the remainder can be employed with either. All those for use with incoming junctions using m.f. signalling are connectible with two of 12 incoming tone control units 1MFCU common to all such IREG registers of the exchange, one of the two units accessible to a particular register IREG being nominated first choice, the order of choice being changed at regular intervals. Each incoming transmission group has access to six incoming registers of the appropriate kind in the particular router RTR, and each transmission group incorporates means responsive to the idle or busy states of the six registers and other means for presenting those registers for possible use according to one order of choice or another order of choice (reverse) in appropriate circumstances for security reasons. All incoming transmission groups, whether in use with m.f. or decadic junctions are seized by a line loop condition. When a m.f. incoming relay group is seized, the group will always try to choose an idle register whose first choice incoming multi-frequency control unit IMFCU is available for use. Incoming decadic transmission groups are arranged to extend a back-busying condition whenever their respective six registers are all busy. While this back signal exists an alternative junction may be taken into use by the calling exchange. This feature is not provided for the m.f. junctions. All incoming transmission groups are arranged to pass an appropriate route-indicating signal to any register taken into use, for use in enabling transit calls to be serviced. One special feature afforded by the system enables a line-man to signal over a m.f. junction by using loop-disconnect signalling. This is accomplished by dialling a special digit which causes the register to annul the m.f. signalling requirement and permits the register to respond to digits in the decadic form. Sending.-Available to the 275 registers of the exchange are 90 senders SDR for decadic impulsing over outgoing junctions and 14 outgoing tone units OMFCU for m.f. signalling. The tone units OMFCU are generally available to the registers via the senders SDR and a 30- wire line interconnects the register via a sender to a tone unit when in use. Each register has access to nine of the senders and each sender has access to two of the tone units on a first and second choice basis. It is emphasized that m.f. tones to be transmitted pass via the sender, appropriate register and the corresponding transmission relay group to the switching system for transmission out over the appropriate junction. Likewise decadic pulses from the sender are transmitted via the register to a particular outgoing junction. The exchange is however provided with two by-path lines ABP and BBP which can afford a direct link beteen the outgoing m.f. tone unit and the register at present involved with