Patent GB-747173-A (GB)
Title: Automatic switching system
Inventor: OBERMAN ROELOF MAARTEN MARIE
IPC: H04Q3/42
Filed: 1951-05-25
Abstract: 747,173. Automatic exchange systems. STAATSBEDRIJF DER POSTERIJEN, TELEGRAFIE EN TELEFONIE. May 25, 1951 [June 16, 1950], No. 12348/51. Class 40 (4). In a system in which incoming lines obtain access to final selectors via incoming and intermediate selectors, an incoming line seizes one of a plurality of control circuits containing a switch which is set in accordance with digits representing the group of final selector outlets to which access is desired; this switch connects busy contacts of all final selectors having access to the wanted group, to busy contacts of corresponding groups of intermediate selectors, and these are in turn connected to the banks of the incoming switches; the incoming selector then hunts its bank for a marked outlet which thus has access over an intermediate selector to a final selector serving the wanted group. As shown, Fig. 1, 273 incoming selectors are divided into three groups of 91 multipled selectors IK. Groups of 13 outlets from each multiple are respectively fed to seven groups of intermediate selectors TK, each group thus comprising 3 X 13 selectors. Each group of intermediate selectors has access to a final selector EK of each hundreds group, the final selectors of each hundreds group being multipled in groups of seven. An incoming selector when seized calls in, over the finder switch KZ, a control circuit BC in which the switch BK is set in accordance with the first two digits of the wanted number. The outlets from the seven banks of BK are connected to busy contacts of the respective outgoing selectors, Fig. 2, and connections from these via the banks of BK mark the corresponding groups of switches TK. This marking is then applied via busy contacts of the switches TK to all outlets of the switches IK giving access via free switches TK to free selectors in the marked groups. The switch IK thereupon hunts for this marking which when it is reached operates T to stop the switch. The selected intermediate switch TK is then set in accordance with the first two digits of the wanted number. The final selector EK may be set directly by the last two dialled digits or via a register. More than one control circuit being provided it is arranged that incoming selectors must be set on a one-at-a-time bases, this being effected by a chain of relays VR in the respective control circuits so arranged that only one such relay can be operated at any one time. Use of spare levels. The nine remaining outlets of switches IK, Fig. 1, may be multipled over -the whole of the incoming selectors and taken direct to overflow final selectors for high density traffic groups. In the event of all regular final selectors of the group being busy, the switch BK is driven to an overflow position from which it directs the incoming selector to the overflow group. In another alternative, these positions may be used for routing interexchange traffic. If some hundreds groups of final selectors are not taken up by subscribers they may be used as overflow selectors for high density traffic groups. A typical method of allocating spare outlets is worked out in full in regard to a trunking system for a seven thousand line exchange having four groups of 56 incoming selectors and seven groups of 40 intermediate selectors.