Patent GB-1264675-A (GB)
IPC: H04Q3/00
Filed: 1969-05-01
Abstract: 1,264,675. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 1 May, 1969 [3 May, 1968], No. 22251/69. Heading H4K. In a three-stage network having a plurality of BC links between each B and C switch whereby there are a plurality of possible paths through each B switch between a prescribed inlet and outlet of the network, path finding is effected with the aid of a set of AND gates which each have one input selectively connectible to an AB link to which a marked inlet has access and which each have their other input selectively connectible to a first BC link to which the marked outlet has access. The gates are connected to a one-only selector which selects the first gate having both its inputs marked as free. If none of the gates indicates a free path, each of the " other " inputs thereof is connected to a second BC link to which the marked outlet has access and so on until a free path is found. Mechanically latched cross-bars are used in the switching network. General operation (Fig. 5).-The inlets to the second stage switches SS1 ... SS8 emanate from first stage switches which are identifiable by the prefix digits viz link p1.1 is the first link from the first A switch while p16.8 is the eighth link from the sixteenth A switch. The pairs of links e.g. s1.1, s<SP>x</SP>1.1 between a B and a C switch e.g. SS1 and ST1 are apparent from the drawing. In order to connect a line attached to an A switch to a particular junctor AL1 attached to a C switch ST1, a marker MQ closes those contacts cp1.1 ... cp1.8 which connect the first inputs of AND gates D1 ... D8 to the AB links p1.1 ... p1.8 leaving the A switch in question. In addition contacts ct1.1 ... ct1.8 are closed to connect the second inputs of the AND gates to the first choice BC links s1.1 ... s8.1 which terminate on ST1. If any of the link pairs connected to an AND gate are free (absence of potential thereon) an indication is given to one-only selector CTC whereafter the selected path is set-up in the order C, B, A. If none of the link pairs are free, a timer eventually connects the second inputs of the AND gates to second choice BC links s<SP>x</SP>1.1 ... s<SP>x</SP>8.1 by closing contacts cu1.1 ... cu1À8 whereby a new path testing can be effected by the AND gates. Particular description.-It is assumed that a calling subscriber has been connected via the network to the calling side of a junctor ALI (Fig. 8), that the junctor has been connected to a register EN and that the register, after reverting dialling tone, has received the identity of the called party. The register seizes the marker (lower portion of Fig. 8) by bringing-up relay mg which thereupon connects earth to all points marked with a black dot. Relay tm (Fig. 7) follows in order to disconnect the second choice link selecting relays cu1 ... cu4 (Fig. 8). Relays na ... nf (Fig. 8) come up in turn and hold. Meanwhile earth is applied over contacts mg2, mg3 to the register and from there to the junctor so that its called-side appearance on the C switch frame can be identified by one of relays sv1 ... sv16 (particular outlet level) and one of relays ct1 ... ct4 (particular switch). The operative ct relay closes its contacts e.g. ct1.1 ... ct1.8 (Fig. 7) in order to connect the first choice links terminating on the C switch ST1 to the second inputs of the AND gates D1 ... D8. The register supplies the called party's number in binary code to hundreds, tens and units relay counting chains ua/ud, da/dd and ca/cd located in the marker. Contacts of these relays are formed into trees P1, P2 whereby one of relays ch1 ... ch16 (particular inlet level to A switch) and one of relays cp1 ... cp16 (particular A switch) comes up. The operative cp relay closes its contacts e.g. cp1.1 ... cp1.8 (Fig. 7) in order to connect the links emanating from the called party's A switch to the first inputs of the AND gates. As a result of the above identifying operations, relays sb (Fig. 7), tb, ta and ck come up in series with the operative sv, ct, cp and ch relays. Relay tz (Fig. 7) follows. If any of the links are busy i.e. at earth potential, then the corresponding path indicating relays cs1 ... cs8 will be short-circuited but provided that the two links connected to an AND gate are both free (absence of potential) then the corresponding cs relay will operate. One such relay is chosen by relay chain mv1 ... mv8, whereafter tz drops in order to prevent tm from slowly releasing. If none of the paths are free, tm does drop after a determined time in order to allow the second choice links to be tested by virtue of the operation of the cu relay (Fig. 8) corresponding to the already operative ct relay. The closure of contacts e.g. cu1.1 ... cu1.8 allows this test to proceed. Assuming that a first choice path is available e.g. links p1.1 and s1.1 then the relapse of tz causes nr (Fig. 8) to come up. (This presupposes that the called party has tested free as indicated by closure of contact di.) Relay nx comes-up followed by ny. The former causes connection magnet VT1 (Fig. 9) to operate and thus release any previous connections over its level and the latter causes select magnet HT 1 to operate and so connect the called-side appearance of the junctor AL1 to the first of the first choice links s1.1. (It will be remembered that the particular C switch outlet and the particular C switch are denoted by the operative sv and ct relays, in this case assumed to be sv1 and ct1 and that the path of BC link identity is denoted by the operative mv relay e.g. mv1.) The operation of ny however causes na to fall back whereby nx and ny drop in turn to remove the operating current from the magnets. nb Drops whereby nx and ny can again operate but this time their contacts nx1, ny2 direct operating current to the connection and select magnets e.g. VS1, HS1 of the B switch lying in the selected path. The repeated operation of ny causes nc to fall back whereby nx and ny again drop in turn to remove the current from the magnets. nd Drops whereby nx and ny come up yet again. This time their contacts nx1, ny2 direct operating current to the connect and select magnets in the A switch so as to finally complete the connection from the called line to the called-side of the junctor. With ny still up, ne falls back, followed by nx, ny and nf. Relay fc comes-up to indicate end of setting-up connection whereupon the register releases mg and the marker restores. The register disengages from the junctor which then takesover supervision of the call. Referring back to the operation of a second choice relay cu, it will be seen that the only alteration to the above described operations is that instead of a C switch select magnet such as HT1 being operated, a magnet such as HT9 will be energized and that instead of a B switch connection magnet such as VS1 being operated, a magnet such as VS5 will be energized.