Patent GB-1126209-A (GB)
Title: Improvements in or relating to telecommunication systems
IPC: H04Q11/04
Filed: 1966-04-22
Abstract: 1,126,209. Automatic exchange systems. INTERNATIONAL STANDARD ELECTRIC CORP. 22 April, 1966 [28 April, 1965], No. 17682/66. Heading H4K. In a multi-exchange system having some privileged subscribers who retain their own numbers irrespective of where they may be in the system, each exchange includes a store in which the numbers of those privileged subscribers who happen to be within the area served by the exchange are written together with the address of the lines which are temporarily allocated to them. The system may be for example a military network, the privileged subscribers being senior officers. General description of system.-This includes a plurality of exchanges XA to XK arranged as shown in Fig. 4. Some of the exchanges act as local exchanges, e.g. XC, which have subexohanges, i.e. concentrators, e.g. H1, C2 connected thereto. Other exchanges such as XA, XE, XJ serve as tandem exchanges and do not have any locally connected subexchanges or subscribers. The system operates on a TDM basis using PCM for interexchange signalling and speech. The exchanges each include buffer stores attached to the incoming and outgoing junctions so that time-slot transposition can be effected. Within an exchange, serial or parallel data transfer can take place. A full description of the exchanges will be found in Specifications 981,175, 980,029, 972,237 and 960,511. General description of system operation.-It is assumed that one of the privileged subscribers is located in the concentrator area H2 of local exchange XH and that the line AE has been allocated to him. The subscriber's personal number and the address of line AE are written into a core store located in exchange XH by an operator. It is further assumed that a calling subscriber AT wishes to call the privileged subscriber (hereinafter referred to as AE, although AE is not in fact his number). In the usual way a free time slot on one of the junctions h1 between H1 and XC is allotted and the particulars of the call are recorded at XC. The latter's special store, which contains the numbers of privileged subscribers who are at present within XC's area, is scanned. Since in this case there will be no match between the called and stored numbers, XC's control circuit initiates the transmission of a search order over each of the junctions be and cf. The search order consists of 16 bits for the called party's number and 2 bits indicating that a search for the location of this number is taking place. The total of 18 bits is divided into three groups of 6 bits each and each group is transmitted twice for error-checking purposes. The time taken to transmit an order occupies 6 time frames. The order is transmitted during a so-called " service time slot." This will later be used for speech between the calling and called parties and another free time slot will have been designated as the service time slot. Each exchange includes a scanner which constantly scans the currently designated service time slot on each of the junctions connected to the exchange. Consequently, the considered search order will be detected and stored at exchanges XB and XF. Again no match will be found so these exchanges' logic circuits retransmit the search order over all the outgoing junctions except that one which corresponds to the incoming junction over which the search order was received. The search order remains stored in each exchange through which it passes. Eventually, the order reaches XH where a match is found. A return-order is sent over that junction, say, eh, on which the search-order arrived. At XE, the return-order is passed on to the junction which was used for the original incoming search-order and so on back to XC. The latter then sends over all junctions an end-order. (The return and end orders are similar to the search order except in the value of the last 2 bits). Each exchange which receives an end order passes it on after clearing its store of the search order. Those exchanges through which the return-order passed, however, utilize the end-order as an indication to set up a " permanent " connection over the service channel on the various chosen junctions between H1 and H2. A new service channel is designated for each of these junctions. Thereafter the call is completed in the usual manner. The logic circuitry required in each exchange for effecting the above described processes is described with reference to Figs. 5-14 (not shown), a somewhat simplified schematic of the logic being depicted in Fig. 3 (not shown).