Patent GB-989336-A (GB)
Title: Improvements relating to automatic telecommunication switching systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/62
Filed: 1960-07-18
Abstract: 989,336. Automatic exchange systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. July 3, 1961 [July 18, 1960], No. 25065/60. Heading H4K. In an automatic exchange, switching equip. ment is organized in sections, via any one of which a subscriber can gain access to links over a plurality of routes, a connection being set up via a route in a section, a link and another route in a section (the two sections may be different but in the detailed embodiment the same section is used on both sides of the link which is thus associated with the section, so that in effect each section forms a self-contained exchange capable of setting up any call). Control equipment on receipt of the identities of the calling and called line examines all sections and selects a free route in each section. The control equipment also examines traffic conditions in all the sections and selects a suitable section on the basis of these conditions and selects an appropriate link which is used together with the selected routes in the selected sections to complete the call. As shown, Fig. 5, m sections are provided each capable of providing a connection between any pair of subscribers. Each section is divided into x units each unit being divided into n groups of line connector switches L/C. Each group of connector switches comprises r connector switches giving access to a group of subscribers lines. All the connector switches of a unit are reached by group connectors G/C. The group connectors are interconnected by links such as L1-1, L1-x, Lx-x, the first and last being used for intra-group connections and the middle one for inter-group connections. The link circuits may contain the feed-bridges and the connections between the calling and called side are symmetrical about the links. In a typical 10,000 line exchange the switches are all 100-point switches. With m = 4, n=20, r=5, x=5, each unit serves 2,000 lines using 5 x 20 line connectors L/C to which access is had from the 100 outlet group connector switches. A group of links is provided for each inter-group or intra-group possibility. For equalizing traffic each 100 group of subscribers lines may be divided into two sub-groups P, Q the first sub-group lying in the same unit in all sections, but the second sub-group having a slipped multiple whereby they occur in different units in the different sections. When the select and control equipment has the information necessary to set up a call it chooses a section which can most conveniently set up the call, on the basis e.g. of which section has most free links at the time; or to avoid taking last choice switches into use until all other sections have only last choice switches. In a T.D.M. system the choice of section might be on the basis of the most advantageous pulse position available. Alternatively, the sections may be taken into use in accordance with a priority scheme. The detailed description relates to a system of the first type. General method of operation, Fig. 6.-Each group of lines LL is provided with a start circuit ST, operable when a line is calling to cause an allotter AL to seize a dial path DP which causes a register hunter RH to seize a face register REG and a line hunter LH to find the calling line. On the basis of the setting of LH and the group to which the hunter belongs the calling line identity is registered in REG. The register also receives the dialled digits over the dial path DP. When a significant number of digits has been received by the register, it is coupled under control of a scanning circuit RSC to a line location identifier LI, when this is free, and passes thereto the called and calling subscribers' identities. The identifier then passes to the route selectors Rs of all sections the first two digits of the called and calling subscribers and information as to whether they belong to P or Q sub-groups. The route selectors then determine the identities of the line groups concerned and hence also the units concerned and thus the group of links which has to be used. The route selectors are fed with the free or busy conditions of all the line connectors and select a free one in each of the line groups concerned. A traffic summator TS receives the free or busy condition of all the links in all the groups over wires w and selects the wires w for the inter- or intra-unit connection required and feeds their outputs to a selector SS. This output is inhibited if the group concerned has no free line connector. The selector SS has TS inputs from all sections and selects that section which has most free links suitable for the connection. In the route selector for the selected section a controller selector CS knowing the group of inter-unit links required selects a free ring and tone circuit (one of RTA ... RTC) capable of serving this group. This circuit takes into use a controller LOC which is then fed with the identities of the link group and the necessary settings of the group connectors and line connectors. The link group identity is used to mask corresponding outlets in the switch CSL which thereupon hunts to connect a free link to the ring and tone circuit in question. The control circuit LOC then causes the group and line connectors to be set by the revertive impulsing method and then leaves the connection under control of the ring and tone circuit until the called party answers or the caller hangs up. The ring and tone circuit leaves the call under control of the link circuit if the called party answers. Inter-exchange calls .-Junctions are connected directly to group connectors. Calls to such junctions are set up under control of trunk controller TRC in a similar manner to that described above, but without the use of ring and tone controllers. The circuit LI contains a translator TX for determining the position of the required outgoing junction and the routeing digits to be sent. The trunk controller TRC does not immediately switch through since this would release the register and there may be further digits to be sent. The trunk controller instead waits until the end of the next interdigital pause, sends out such digits as it has received, signals its own identity to the register which then dissociates itself from the connection until it receives its full quota of digits. The register, knowing the identity of the trunk controller, may now reassociate itself therewith to pass the remaining digits. Changed number calls.-The translator may contain means whereby the location of the subscribers line or the line connectors can be changed without changing the subscribers' directory number. PBX lines.-The translator TX may also be enabled to recognize PBX numbers and being fed with the free or busy conditions of all PBX lines may make a choice of a free line and inform the route selectors accordingly. A special signal is however sent to the controllers to ensure that should an indicated PBX line meanwhile become busy whilst the setting up is taking place, busy tone will not be sent and that the register will again try to set up the call to another PBX line. Detailed circuits are provided, the selectors being motor controlled uniselectors and the controlling equipment being a high speed electronic arrangement. In a modification the selection of the section takes place at the line terminals, each line being connected to a cross-point device such as a cross-bar switch having outlets leading to different sections. In a further embodiment in which the sections are constituted by T.D.M. systems, each line could be connected to gates to a number of T.D.M. highways. Specifications 989,338, 989,339 and 989,340 are referred to.