Patent GB-1382308-A (GB)
Title: Market for communication switching system
IPC: H04Q3/545
Filed: 1972-03-30
Abstract: 1382308 Automatic exchange systems GTE AUTOMATIC ELECTRIC LABORATORIES Inc 30 March 1972 [1 April 1971] 15232/72 Heading H4K In an exchange employing a multistage relay switching network, wherein each relay has a normally open pair of contacts connected in series with its hold winding and a hold conductor, there is provided marker apparatus for selecting paths and establishing connections between a first set of terminals and a second set of terminals through a first plurality of switching stages via intermediate junctors and a second plurality of switching stages arranged in tandem between the two sets of terminals. The marker apparatus is arranged to select all free paths between one terminal of the second set and free intermediate junctors via the second plurality of switching stages, and to mark all such free junctors, there being only one possible path between a terminal and a particular junctor. To complete a connection through the first plurality of switching stages to a particular terminal of the first set, the paths from the particular terminal to the junctors are sequentially tested until a free path is found which gives access to one of the marked junctors. A connection involving a single path between one terminal of each set has then been selected and the connection can be established. Free paths are selected by using coincidence logic gates of which the inputs are connected to the hold conductors associated with every crosspoint relay, the potential on the hold conductor indicating the free/busy state of the associated speech link. Counters are associated with the sequential path test through the first plurality of switching stages and these enable the exchange common control to identify the particular path and junctor chosen. General description of exchange (Fig. 1).-The marker apparatus as above described forms a terminating marker for completing a connection from one of a plurality of originating junctors O, J (first set of terminals) to one of a plurality of subscriber lines (second set of terminals). The exchange has two sets of main switching groups: line groups which each include three stages A, B, C (the second plurality of switching stages) and select groups which each include three stages A, B, C (the first plurality of switching stages). A pair of terminating markers is provided which serve up to 8 select groups and up to 10 line groups. The terminal markers work alternately, one of the pair being selected for each termination and means are provided to prevent the markers from working simultaneously. In the case of one marker becoming faulty, the other marker can handle the entire traffic load. The operative functions of each terminating marker are described with reference to Figs. 6 and 7 (not shown) and will be clearly illustrated below in a description of the processing of a local call through the exchange. An originating marker controls the connection of either a local subscriber or an incoming trunk to a register junctor via an originating junctor. The marker first performs a scanning operation to identify a calling line. This operation is performed on the " pull conductors " of the line matrices; such conductors interconnect the series combination of a diode and a pull winding of a relay in adjacent line matrices (see Fig. 8). For a detailed description of the line identifier reference is directed to U.S.A. Patent Specification 3,211,837. The identified line is then connected through A and B stages of the line group to an originating junctor and then via a register connector R to a register junctor RJ, after the marker has first selected a free path between the calling line and a free junctor. Similarly incoming trunks are connected via a trunk register connector to a register junctor. When the routing information received by the register junctor has been transferred to common control via a multiplex system the terminating marker is sent sufficient information to select and make a connection between an originating junctor, or an incoming trunk, and the required local subscriber or outgoing trunk. Once the terminating marker has completed its operation, i.e. the speech path has been established, it informs common control and releases from the matrix groups. Because both originating and terminating markers require access to the line group matrices, logic circuitry is provided to prevent simultaneous working of the two markers in the same line group. If an originating marker is working in the line group to which the terminating marker requires access, the terminating marker will mark a reserve bus of the line group, thereby preventing a further originating marker access after the current access is terminated. Trunking.-Each line group (Fig. 2) provides access between 1000 subscribers and 120 terminating junctors and 140 originating junctors. Each 20 subscriber lines are connected to a limited availability crosspoint matrix A which gives each line access to only five out of the ten outlets of the matrix. The outlets from 10 such A matrices are connected to 10 B matrices which each have ten inlets and 8 outlets. Each line has access, therefore, to only 5 B matrix units. Also it is arranged that no line has access to more than one of each of the following pairs of B matrix units: 1 and 6, 2 and 7, 3 and 8, 4 and 9, and 5 and 10. The outlets from each B matrix are arranged in two groups of 4. One group together with the groups from the 49 other B matrices are assigned for connection to originating junctors via a jumper frame CCF. The other 50 groups of four outlets are connected to 20 C matrices each having 10 inlets and 6 outlets, each outlet being for connection to a terminating junctor. There is also provided a register connector group of four matrices each having 5n inlets and 5 outlets where n has a maximum value of seven. Each selector group (Fig. 4) provides access between 300 inlets and 800 outlets, the linking being arranged as shown. Each matrix provides full availability and the 800 C outlets are coupled to the terminating junctors via a distributer arrangement OGF, some outlets being coupled to outgoing junctions. The matrix groups are each formed from a number of A, B and C units, e.g. A11 to A10 shown in boxed form in the Figs. 2 and 4, each unit being packaged on one printed wiring card. Setting up a local call (Figs. 1 and 8).-A calling line is identified by the line identifier part of the originating marker and the originating marker accesses the line group matrices A, B and R via the connect and access circuitry. All B unit outlets accessible to the A switch input to which the calling line is connected are then scanned. Because all B outlets associated with busy AB links, with unaccessible AB links, and with R units of which all the register junctors are busy, are electronically busied (it is not stated how this is achieved), the free B unit outlets constitute idle links to originating junctors and one of these links is selected by the scanning. The marker then scans the outlets of the R unit defined by the B unit outlet and makes a register junctor selection. This defines a unique path and the subscriber is connected through to the register junctor by the marker, which, on completing the connection, sends a block of information to common control including the equipment identity of the calling subscriber and identity information concerning the originating junctor and register junctor. In common control, a look up table is consulted to determine the address of the storage cell associated with the register junctor in a memory which forms part of a register sender complex and thereafter the information is stored in this cell. A class of service translation is then performed. Included in the class of service is information concerning dial tone, party test, coin test, type of ready to receive signalling required, type of receiver required, customer special features and control information used by the digit analysis and terminating phase of the call processing function. Part of the class of service information is stored in the junctor memory cell and part of it is transferred to the register sender for controlling the register junctor. Prior to this the class-of-service information has been analysed to see if any special action is required, e.g. non-dial line or calls barred. The register junctor is informed of any special services that the call must have and the junctor then returns dial tone and the subscriber proceeds to key or dial the number of the desired party. After receiving the first three digits a first translation is performed to determine the type of call, e.g. local or trunk. As this is a local call the register sender will be instructed to accumulate a total of seven digits and to request a second translation. The common control then utilizes the information received in the form of digits to identify the A matrix input of the line group to which the called subscriber is connected. Sufficient information is then supplied to the terminating marker to enable it to select and connect a free path between the identified called line and the originating junctor connected to the calling line. The terminating marker operation commences with a check on the line group to which the called subscriber is connected to determine whether an originating marker is working in it. When the line group becomes free, the called line is checked for busy and if it is not, the marker assigns itself via the connect and access circuitry to the A, B and C matrices of the line group and to the line circuit of the called subscriber. In the case of called PABX lines, the marker first performs a scanning operation of the lines to the PABX and selects an idle one before accessing the line group matrices. For all other lines such a scanning operation is not required. The 5 line group AB hold conductors and the 20 BC hold conductors avai