Patent GB-1401129-A (GB)
Title: Telecommunications systems
IPC: H04Q3/00
Filed: 1973-02-23
Abstract: 1401129 Automatic exchange systems SIEMENS AG 23 Feb 1973 [29 Feb 1972] 8957/73 Heading H4K In an exchange system having call diversion facilities, modification of an existing call diversion is effected from the station to which calls are being diverted and a check is performed by central control equipment to ensure that the request for a modification is in fact coming from such a station. This check is particularly performed by identifying the requesting station using the exchange equipment, and transmitting the information to the relevant central control equipment. Cancellation of a call diversion can only be effected from the two stations involved in the diversion and the diversion is set up from the speech station from which calls are to be diverted. Setting up a diversion.-Assuming station N 1  wishes to divert his calls to station N 2 , subscriber N 1  dials or otherwise sends (no details given) a special initial characteristic together with the directory number of the station, N 2 , to which the calls are to be diverted. The central control of subscriber N 1 's exchange performs a calling line identification (no details) and then causes the address of the call divert station N 2  to be stored in a storage device SpEl allocated to the calling station N 1 . Modifying of existing diversion.-It is assumed that subscriber N 1  wishes to alter the divert station from station N 2  to a station N 3 , that subscriber N 1  is present at station N 2  and that stations N 1 , N 2  are connected to different centrally controlled exchanges A1, A2. First the directory number of the station N 1  is dialled followed by a special characteristic or vice versa, and then the number of the new divert station N 3  is dialled. As a result of this action the exchange system functions as follows: when the subscriber at station N 2  goes off-hook, a connection is established in known manner via a subscriber circuit TS2 and the crosspoints in a switching stage K2 to a circuit LU2 from which the digits transmitted by station N 2  are coupled via register coupler SK2 to a free register Sp2. The contents of register Sp2 are analysed either in that register or in a central control device ZS2 and it is determined a connection must be established to exchange A1, this connection being made via group selectors VK2 and VK1 to a circuit LU1 of exchange A1. The digits of the station N 1  dialled at station N 2  are then transferred to and stored in register Sp1, but because a special characteristic has been signalled from station N 2 , the dial or selection analyser of exchange A2 emits a special signal to exchange A1 so that no attempt is made to establish a connection to station N 1 ; instead a comparator VG1 and the store SpE1 are connected to central control device ZS1. The digits of station N 1  stored in register Sp1 are then transferred to the comparator device VG1 and concurrently, by the emission of a backward signal from central control device ZS1, the identification of the station N 2  in exchange A2 is initiated with the out of central control device ZS2. The identification result is fed via junction VL12 with the aid of register Sp2 and a converter contained therein, into register Sp1 and thence to the comparator VG1. Then, when both addresses N 1  and N 2  are present, comparator VG1 establishes whether the address of station N 2  is stored in the storage device SpEI as the call divert station for station N 1 . If this is so, the previously dialled address of the new diversion station is called up from register Sp2. In a variant embodiment, the number of the new call divert station is not initially dialled at station N 2  but a request to send signal is sent to station N 2  once the comparator checks have been made. The address of the new divert station is then transmitted straight to store SpEI via register Sp1 and comparator VG1 without being stored at exchange A2. Cancellation.-To cancel a diversion the number of the station N 1  from which calls are being diverted is dialled/selected followed by a cancellation characteristic or vice versa. A check by means of a calling line identification is performed by central control 251 to ensure the cancellation came from one of the two stations involved in the diversion and the diversion is then cancelled assuming a positive check. Other alternative features.-Store space may be provided so that the present and the preceding divert station may be stored for a given station. This enables cancellation or modification to be achieved from either the present or preceding divert station although all calls are diverted to the present divert station.