Patent GB-1162782-A (GB)
Title: Telecommunication Exchange System with Concentrators
IPC: H04Q3/00
Filed: 1968-01-11
Abstract: 1,162,782. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 11 Jan., 1968 [17 Jan., 1967], No. 1739/68. Heading H4K. In a system comprising a plurality of satellite exchanges connected via respective groups of two-wire trunks to a parent exchange, the latter includes a control circuit in respect of each satellite in addition to its own central control circuit. In order to set up a connection from/to a satellite subscriber, the corresponding control Ki at the parent exchange causes the (external) control Ka in the satellite and the central control ZSt, GM in the parent to search for paths through the satellite and parent exchange's switching networks to free trunks extending therebetween; selects one of those trunks marked as a result of both searches; and transmits the identity of the selected trunk over an auxiliary junction Zk to the satellite and over an information bus IV to the central control ZSt and marker GM, whereafter new paths to this trunk are selected and connected through. The holding time of the central control and marker are thereby minimized since they are only required during path searches through the parent exchange's switching network and not during satellite/parent signalling or path searching in the satellite. Particular description; outgoing call from satellite.-The off-hook condition of a calling satellite subscriber T is detected by a scanner which causes the external satellite control circuit Ka to demand, over auxiliary junction ZK, the service of its associated internal satellite control circuit Ki when this, becomes free. The identity of the caller is recorded in Ki. The latter requests Ka to initiate path seeking by sending offering signals over a guide wire network associated with the satellite's switching network KKF, whereby free junctors VK (and hence trunks VL) become marked. In each such junctor a relay responds to the marking so as to loop the trunk. The loop is effective, in the incoming junctor LUe in the parent exchange, to bring up a relay which applies a mark to a wire extending to a diode coincidence gate (Fig. 2, not shown). When the marker GM becomes free, Ki requests it to initiate path seeking by sending offering signals from all free junctors VS via switching network EKF's guide wire network towards the incoming junctors LUe. In the free junctors LUe, a relay comes up to the offering signal so as to apply a marking to the other input of the junctor's diode coincidence gate. Ki selects one of the junctors LUe whose gate has been opened and informs Ka and GM of the identity of this junctor. Ka and GM then effect path-search and path-connect operations between respectively the subscriber and the chosen trunk and between the chosen trunk and a free junctor VS. The latter is thereafter connected to a register and the call is completed in the usual way via group selector RKF. Incoming call to satellite.-If for example parent exchange subscribers Ta calls satellite subscriber T, all the data for the call is transferred to the internal control Ki appertaining to the wanted satellite and the markers GM and RM and the originally seized register are released. Ki interrogates Ka as to the free/busy condition of T and if it is free requests that free trunks be marked as described above. Similarly, GM is called in to find the free trunks accessible to the junctor VS that is already in use for the call. When a trunk which is free and reachable from both ends is selected, paths through the switching networks to this trunk are then chosen and switched through in exactly the same manner as before. Metering.-Each trunk has an associated  store into which the identity of a calling satellite subscriber is entered from Ki. Whenever a metering pulse occurs, it causes the store to be read-out so that an entry can be made in that subscriber's meter store.