Patent GB-920072-A (GB)
Title: Communication switching system
IPC: H04Q3/52
Filed: 1959-12-22
Abstract: 920,072. Automatic exchange systems. GENERAL TELEPHONE LABORATORIES Inc. Dec. 22, 1959 [Dec. 22, 1958], No. 43538/59. Class 40 (4). In an exchange in which line circuits are scanned and a register is seized over the scanner for a calling line, a connection is set up over cross-point switching networks from the calling line to a junctor whereupon this connection is used to transport the called line identity so that a connection may be established over crosspoint networks from the junctor to the called line. As shown in Fig. 1 the exchange divides its switching circuits into groups A, B, and C, each handling 1000 local lines and 100 trunk lines. Each group has its own slow speed time division multiplex control circuit (see Fig. 2), and all groups are served by a common circuit 150 which provides for toll ticketing and translation. The outlets from each group are arranged in levels DA1 to DA5, DB1 to DB5, and DC1 to DC5, with 100 trunks to each level. The trunks EA, EB, EC provide access to each group from all other groups over an IDF. Outgoing trunk circuits 131 are available over two levels of each group over trunks ED and EE. Fig. 2 shows the block schematic for group A with the common control apparatus shown in the bottom righthand corner. The 1000 local lines, over line circuits 202, are connected by a line frame 207, 208, comprising the cross-point stages shown in Fig. 3. Each group of 100 lines in sets of ten connect over 10 x 6 matrices to five 4 x 10 and one 5 x 10 matrices to concentrate the 1000 inlets to 250 B links. The B links are connected to a line group selector LGS which, as shown in Fig. 4, comprises ten groups of five 5 X 10 matrices the 50 outlets of each oddnumbered group being multiplied with the corresponding outlets of all other odd-numbered groups and the even-numbered groups being similarly multipled to give 100 outlets to links C. Incoming trunks over circuits 205 are connected to a trunk group selector 212 seen in Fig. 3 where in groups of twenty the trunks connect over five 20 X 20 matrices to links H. The links H and C are connected to the trunking levels DA1 to DA5 over the level selector 214. Each of the H and each of the C links is connected over a cross-point to one trunk in each of the trunking levels (see Fig. 4), each level having a hundred trunks. Over the IDF each level is connected to an inlet trunk EA, EB or EC to a group, or to an outgoing trunk circuit over ED, EE. Each outlet from the IDF is connected to a junctor (see Fig. 5), which functions to hold the cross-points of a connection and to provide amplification. Each group is accessible from other groups over one hundred such junctors, shown at 216 in Fig. 2 and at J1 to J100 in Fig. 5, and these are connectible over five 20 x 25 matrices to five commoned groups of twenty-five 1 x 10 switches giving access to any one of the 250 B links. Referring from here onwards exclusively to Fig. 2, control is effected over the dash-line connections by means of a slow speed multiplex system. A scanner 220 picks out a calling line or trunk and registers its identity in a temporary store 221. Over selector 222 one of twenty registers 223-1 to 223-20 is seized and records the calling line identity and the called line identity as dialled over the calling line. After one, three, seven and ten digits the register interrogates translator 280 in the common control circuit and receives guidance. A local call uses seven digits which are coded and over connector 225 are transferred to the translator 280 served by number group registers 282-1 to 282-40 each of which store 1000 directory numbers. The translator is marked free or busy to the connector by a blocking circuit 283. The appropriate number group store receives three digits and returns information giving the markings in the thousands, hundreds, tens, and units groups, and also indicates ringing frequency or code, whether the call is to a PBX group, and whether the call is to be connected despite busy conditions. This information in a full ten-digit number is sent to the register in 223-1 to 223-20 which transfers the calling line identity and the thousands group code of the wanted line to a common originating register 226. Such transfer must be permitted by a blocking circuit 231 which ensures that only one connection is established at any one time. A path finder 227 stores the busy conditions of cross-points in the line frame 207, 208 and in the local group selector 210. The B links are tested in sequence and an idle path over the line frame is seized. Each B link connects with ten possible C links to the level selector 214 and path finder 228 connects these ten links to ten trunks in the wanted outlet level indicated by the thousands group code. If a junctor associated with one of the trunks is idle, the trunk and junctor is seized and a connection is established from the calling line as far as the junctor. Blocking circuit 284 restricts search over junctor trunks to one switching group A, B or C, at a time. A path is now available from the register in 223-1 to 223-20 over selector 222, store 221, scanner 220, the calling line circuit in 202, over the connection established to the junctor seized in the wanted switching group, to a terminating register 232. Over this path, when permission is given by the blocking circuit 231, hundreds, tens and units markings are sent to the register 232 together with an indication of ringing frequency or code and whether the call is to a PBX group. Path finder 233 selects a free path between the called line and the link F from the seized junctor. The called line is tested and ringing is called for from circuit 234 and produced in the called subscriber's line circuit from which it is also reverted to the calling subscriber. If the called line is busy the junctor releases and frees the entire connection. Busy tone is then sent from the calling line circuit. The register stays in service for a further 5 to 10 seconds causing the re-connection of dial tone at the end of this period if the calling line is not disconnected. An outgoing toll call is connected in the same manner as a local call to seize a junctor in an outgoing trunk circuit. Toll ticketing information is sent from stores TT which are plug-in units associated with registers 223-1 to 223-20, such information having come from toll ticket store 281 associated with the translator. This information is detected by a scanner 285 working in conjunction with a clock circuit 287, a store 286, and a printing circuit 288. Incoming toll calls and calls for tandem connection through the exchange are similarly controlled. It is mentioned that the registers 223-1 to 223-20 and the path finder 227 use ferrite core storage.