Patent GB-1474267-A (GB)
Title: Telecommunications exchange systems
IPC: H04Q3/00
Filed: 1974-06-14
Abstract: 1474267 Automatic exchange systems SIEMENS AG 14 June 1974 [29 June 1973] 26402/74 Heading H4K In a path selection arrangement applied to a multi-section switching network of the "inverse grouping" type, the manner of selection of intersection links is made dependent on whether a link is to be used as part of a connection between inputs of different switching network sections or is to be used as a "blind" link for a "short path" connection between two inputs of the same network section. Two sections AG1, AG2 of an eleven section network are shown in Fig. 2. Each section has an identical trunking arrangement and is such that each A storage matrix input of a section has access via, in each case, a unique path to all 1000 C stage outputs of the section. The path finding arrangement for the whole network is shown in Figs. 4 and 5, and is formed from three sections VA, VB, VC (Fig. 4) which are connected via a logic arrangement to 10 groups of 10 wires VW scanned by a scanning arrangement EAW1, EAW2 (Fig. 5). Section VA is associated with the A-B interstage links a and comprises for each of the 1650 A stage matrices a power switch KA 1-1650  which is connected to a group of 10 link switches, e.g. KSA 1-10  via a group of two diodes VK, a link switch being in the open state of the corresponding a link is free. Section VB is similarly arranged according to the sub-sections KG of the network and has one power switch KKG1-110 for each of the subsections, each power switch being coupled via diodes to a set of 100 link switches corresponding to the B-C links emanating from the subsection in question. Finally section VC has one power switch KB1-55 for each of 55 groups of intersection links c and each power switch is again coupled via diodes to 100 c link switches. Path finding and path selection then proceed as follows.  Intersection connections.-For two inputs connected to different exchange sections, it is known which two A matrices, which two network sub-sections and which one group of intersection links are to be involved in the call. One therefore proceeds by closing the five corresponding power switches which results in markings being extended to wires in the 10 groups of wires VW which correspond to paths having an a and, or b and/or c link busy. The scanners EAW1/2 are then arranged to scan the 100 wires as a 10 x 10 matrix, the scanner EAW1 scanning the groups and scanner EAW2 scanning the individual wires of a group simultaneously with the wires of all the other groups. Assuming more than one unmarked group VW the scanner EAW1 fixes on a first unmarked group and then applies a busy marking to all other unmarked groups. The scanner EAW2 is then used to find the first unmarked wire of the group, thereby identifying a free one of the 100 paths between the two inlets. A central control then has sufficient information to set up the path. It is emphasized that as the scanners always start from a fixed state and fix upon the first unmarked path a bias in favour of the paths which are scanned early in the scan is introduced into the loading of, in particular the intersection, links (cf. Strowger switches where the outputs at the beginning of the scan are more frequently used). Intersubsection connnections in the same network section.-For such a connection it is not necessary to use an intersection link, but as the connection must extend to a C matrix, one such link has to be allocated as a "blind link". However as one can use any c link extending from the particular section it is possible to base the choice of c link on the expected loading of the links, e.g. one chooses for the first path finding search a group of c links which carries the least into section traffic for intersection connections. Hence the c links are not scanned in a fixed order as in the case of a intersection call. Path selection hence proceeds by operating the two A matrix and two sub-section power switches together with one intersection c link group power switch corresponding to the least loaded group. The scanners are used as above but if no free path is found the selection can be repeated with a different group of intersection links. Connections within the same sub-section.-The path finding arrangement can be used for connecting inputs of two different or the same A matrix simply by only operating the power switches of the VA and VB, or just the VA, sections of the path finding network, the scanners then being used to identify and select free a links and b links as necessary. For such connections an uneven loading of the a and b links does result from the scanning arrangement used.