Patent GB-1365777-A (GB)
Title: Automatic telecommunication exchange
IPC: H04Q3/00
Filed: 1972-08-01
Abstract: 1365777 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 1 Aug 1972 [4 Aug 1971] 35799/72 Heading H4K In an automatic exchange, in particular one employing a crosspoint switching network which utilizes cross-bar switches or reed relay crosspoints, the switching network is divided into sections, to some of which may only be connected subscriber lines and to others of which may be connected subscriber lines and incoming and/or outgoing trunks and/or two-way trunks, the network being characterized in that there is at least one section to which only trunks are connected. All calls take place via links, some of which are used by calls between subscribers or trunks connected to the same sections and others of which are used for calls between subscribers or trunks of different sections. Registers are provided each of which is accessible via at least one of said links and markers use the information supplied by the register to select and establish routes through the network. The registers may only be available via the links between the section to which only trunks are connected and the other sections of the exchange. General description (Fig. 7).-The exchange described is an extension of that described in Specification 1,101,567 and employs for each switching section a two stage cross-bar network involving an overflow arrangement ("entraide") which is similar to the arrangement of Specification 1,044,601. The exchange has five sections, to each of which are connected both incoming trunks ENL and local subscribers. Each section has its own marker LM-1 to LM-5 and associated control circuitry MCA, MCB. A sixth section BLE has connected thereto only outgoing trunks ENL and has access and control circuitry MARC-BLE. A central exchange marker MARO-CEN supervises the individual section markers. Links shown in a group as ALIM interconnect the first five sections with each other, there also being links interconnecting different outputs of the same section. Links also connect the trunk section BLE with each of the other five sections and in this particular arrangement only these links have access to registers REG, as the exchange is a sector exchange in a rural network (Fig. 1, not shown) and handles mainly trunk traffic. In other arrangements, the other links may have access to registers according to the particular traffic load of the exchange. Trunking (Fig. 3).-The trunk section BLE is a switching array with 12 cross-bar switches in its primary stage EP and five in its secondary stage ES, connected in "entraide" such that each ES switch is connected to the EP switches by 20 regular and four overflow links, the verticals of the ES switches being connected to the trunks and the horizontals of the EP switches to the links, to the other sections. Each ES switch therefore has access to any one of the EP switches via one of two interstage links. For further details reference is directed to Specification 1,044,601. Similar trunking may be used for the remaining five switching sections. Setting up a call.-In the particular arrangement shown all calling lines have to be connected first to a link having register access i.e. a link to the separate trunk section. The choice of a suitable free link involves the use of a diode test matrix involving a diode in series with a switch connected between horizontals and verticals, the contact being closed if the link is free (Figs. 5 and 6, not shown). The link is then connected to a free register via a register connector RC, the arrangement being such that the link cannot be seized unless there is a free register associated therewith. The information regarding the required line is then transmitted from the calling line to the register. If an outgoing trunk connected to the special trunk section is not required, the appropriate markers select a path between calling and called lines via a different link, not having register access and once the call is set up the connection to the register access link is dropped. This will occur for all calls to local subscribers. If the links required for local calls do have register access, calls are set up as described in Specification 1,101,567. If an outgoing trunk is required, the trunk section marker selects a path between the appearance of the link connected to the register in use and a suitable outgoing trunk in known manner. The call then takes place via that link. Two way trunks may be connected to said trunk section for outgoing calls and to one of the other sections for incoming calls (Fig. 2, not shown). Duplication of markers.-The separate trunk group is provided with two markers which work alternately on calls for service.