Patent GB-1360477-A (GB)
Title: Telephone systems
IPC: H04Q3/54
Filed: 1971-12-15
Abstract: 1360477 Automatic exchange systems WESTERN ELECTRIC CO Inc 15 Dec 1971 [16 Dec 1970] 58217/71 Heading H4K In a telephone system in which operators can give assistance in customer dialled trunk calls, trunk circuits seized for calls are connected (on seizure) to an operator service centre via a switching network, the identity of each seized trunk is transmitted to the centre and dialling information is routed over the associated trunk via the service centre. The system is such as to allow users to dial trunk calls themselves even when they require operator assistance e.g. for credit card calls, reverse charge calls and person to person calls. The centre can be remote from the groups of trunks which it serves and the service can thus be economically provided on small trunk groups. As shown an operator service centre 100 serves via a remote service unit 113A, a group of trunks between a local exchange 101A and a main exchange 102A, and serves via other remote service units (not shown but connected as indicated at 114B) other groups of trunks between other pairs of exchanges. The trunk group shown may be the only route for calls to exchange 102A originating at exchange 101A or additional conventional trunks may be provided and used for calls not requiring operator assistance. Each of the trunks shown include a trunk circuit 103-0 to 103-99 which initially splits as indicated by the illustrated make contacts its trunk into local and main exchange sections preventing direct connection between the exchanges. The remote service unit 103A includes a 200 x 10 cross-bar switch 108A which can selectively interconnect each of the two parts of each trunk separately and independently to any one of the remote base unit trunk circuits 110-0 to 110-9 each terminating one link to the centre 100. Call processing.-When the local exchange seizes for example trunk circuit 120A-0 for an outgoing call, the associated trunk circuit 103-0 causes a connection to be established between the local exchange side of that circuit and a preselected one of set of ten remote base unit trunk circuits 114A-0 to 114A-9, e.g. the crosspoint between vertical V0 and horizontal H9 is operated to connect the local exchange side of remote trunk circuit 103-0 to say remote base circuit 110-9, the latter circuit having been preselected by a relay allotting chain. The operator service centre which is basically a No. 1 E.S.S. system, detects incoming call and couples a multi-frequency digit receiver 107 to the incoming path. The coupling between each of the remote base trunk circuits 110-0 to 110-9 and the corresponding circuit at the other end to the associated link 114A-0 to 114A-9 is effectively a 4 wire path (two speech wires and "E" and "M" signalling wires) but as described with reference to Fig. 6 (not shown) the E and M signals are converted to tones, transmitted to the other end of the path and converted back to E and M signals. When the multi-frequency digit receiver is connected to the path a wink signal is transmitted over the "E" conductor. The remote service unit repeats this signal back to the local exchange 101A which transmits the called number in multifrequency form over the speech wires to the centre. When these have been received, the centre grounds the "E" conductor releasing a relay in the remote trunk circuit. The release of this relay initiates operation of a multi-frequency under OTP in the remote trunk circuit transmitting three digits to the centre. The digits are stored prior to transmission in 2 out of 5 form in a shift register 201 (Fig. 2B). The first digit stored in stages 1 to 5 and is entered via one of a number of pairs of diodes D5 to D14 in accordance with the state reached in the call. In the present example this is a new call and diodes D9 and D10 conduct to set a "O" in these stages. Stages 6 to 10 and 11 to 15 are set on each occasion to predetermined values via diodes D1 to D4 to store the two digit identity of the particular trunk involved. During transmission the first digit enables two out of five gates FG0 to FG7 gating corresponding tones via a transformer T1 to the speech path, assuming such enabling is not blocked by a 2 out of 5 check circuit 212. The shift register is then shift five steps to the right to position the next digit for transmission and so on. On receiving these three digits the centre processor determines whether the call requires the assistance of an operator and assuming this to be the case an operator position say 109- 1 is coupled to the calling path via a switching network 104A. A multi-frequency outpulser 106 is coupled via the switching network 104A to another idle link say link 114A-0 and transmits to a multi-frequency receiver 108C in the remote service unit control a three digit number, two digits identifying the trunk to which a connection is required and the third digit indicating whether a connection to the incoming or to the outgoing end is required. For the present call the outgoing end of trunk circuit 103-0 is connected via vertical V1 and horizontal H0 to the newly selected link. The number of the wanted subscriber is transmitted over this path and the main exchange portion of the trunk to the main exchange. While this connection is being set up and the called subscriber is being rung the operator can converse with the calling subscriber. In the case of a credit card call the operator may obtain the information she requires and be released from the connection before the called subscriber answers. In this case the links 114A-0 and 114A-9 are both released, the make contacts in the trunk circuit 103-0 (one of which is shown) are operated to directly couple the two portions of the trunk and the relevant cross-bar crosspoints are released. When the called subscriber answers, a fresh connection to the centre is momentarily established and the outpulser in the trunk circuit transmits its identity and a digit signifying that the called subscriber has answered. The processor in the centre enters the time into storage alongside other data already stored in relation to this call. Further fresh connections are established when either subscriber releases from the call or when the calling subscriber sends a switch-hook flash. In the latter case an outpulser 106 is seized and a connection to the local end of the trunk circuit is established and an operator position connected to this connection. In the case of a reverse charge call or a person to person call the operator remains in the connection until the called subscriber has answered. After conversing with the called subscriber she operates a metering commence key to initiate call charging. The trunk circuit will have already established a connection to the centre and supplied the information that the called subscriber has answered, but the processor is programmed to ignore this fact if the operator is still in the connection.