Patent GB-1459299-A (GB)
Title: Telephone exchange systems
IPC: H04M3/44
Filed: 1974-03-06
Abstract: 1459299 Automatic exchange systems SIEMENS AG 6 March 1974 [9 March 1973] 9609/74 Heading H4K Telephone stations having direct call keys for accessing particular other stations in addition to normal dialling facilities include two translators. The first translator is used to provide a called subscriber's address in response to the depression of a direct call key, and the second translator is used when the station is called to operate a call signal associated with a direct call key when the corresponding calling stations address is applied to the translator. Such an arrangement is used in a system interconnecting air traffic controllers' positions wherein a central control ZSE has direct access over signalling wires to station stores S1-Sn positioned at corresponding stations TS1-TSn. Speech paths are set up upon the reply of a called station via a relay crosspoint network ABC. Many special features such as call queuing, conferences, priority break-in, call transfer &c. are provided. Trunks may extend to a PBX or the public telephone system. Station equipment.-Each station has two receivers, one for use by a flight controller and the other for his assistant. Each are provided with separate interrogation keys, clearing keys, conference keys, seizure keys and network appearances but they share a common station number, a key board dialler and up to 10 direct call keys each having an associated lamp. The station store has three origin stores US11- US 13 for storing calling subscribers numbers which are queued in order of arrival, each queue position having an associated lamp. The numbers of the calling subscribers in the queue are not visually displayed. Although only one call may be set up at a time from a station, once one of the two controllers has established a connection the other may initiate or accept a call. Detailed description.-In the following description of the system operation, the headings used correspond to similarly worded headings in the Specification to which reference is directed for a detailed description.  Dialled call between stations.-A flight controller at station TS1 initiates a call by key dialling into a digit store (not shown) in station store S1, and on completion of dialling a service request is extended to central control ZSE. The number of the called station is then signalled to central control, using a 2 out of 5 code, where it is stored in a store ZS. In addition the called number is fed into a target store ZS11 which is assigned to the flight controller. Had the assistant flight controller initiated the call he would have additionally depressed a seizure key B12 to cause the called number to be fed into target store ZS12. Central control accesses the store Sn of the called station and if one of the three origin stores USn1-3 is free compares the number of station TSn stored in permanent store FSn with the number stored in store ZS. Central control then calls up the number of the calling station from permanent store FS1 and feeds it to a free origin store, e.g. USn1 in the called station thereby lighting a corresponding lamp A2n1. Common then releases from the stations pending an answer signal from the called station. Called station answers.-Either controller accepts the waiting call by depressing his interrogation key to call up central control. The number in the origin store USn1 is read and central control accesses the store S1 of the calling station to compare the number in store USn1 with that in permanent store FS1. Central control calls up the called subscriber's number from permanent store FSn and feeds it to the calling station where it is compared with the contents of the target stores ZS11 and ZS12 to cause a corresponding signal to be sent to the line circuit TA1 of station TS1, and further to cause central control to be informed of the result to enable the switching network appearance of both the calling controller and the call accepting controller to be marked. In known manner a marker determines and sets up a free 4-wire path across the switching network. Repeated dialling.-If all three origin stores at the called station are busy, the calling station store S1 is arranged to call up central control at regular intervals to provide for repeat attempts to set up a call. Two subscribers simultaneously call each other.-If a controller dials a number which is already queued in one of the origin stores of his station, the calling request is converted to a call acceptance and the queued call is set up irrespective of its position in the queue. Direct calling.-A single call key is depressed which causes a rectifier wiring board translator to produce the required called station number, which is then stored in the target store as before. The operation proceeds as for a dialled call until the number of the calling station is received at the called station. As was not mentioned for a dialled call all calling numbers are applied in the called station to a rectifier translator and if the calling number corresponds to a direct call key a lamp associated with the key is lit and the calling number is not fed to an origin store. The flight controller accepts the call by depressing the corresponding direct call key to cause the number of the calling station to be produced by the other translator. The cell is then set up in a similar manner to a dialled call. Should the assistant flight controller wish to accept the call, he depresses his interrogation key in addition to the direct call key. Cancellation of a call request.-A waiting call can be cancelled from the calling end by the caller re-dialling, accepting an incoming call or depressing a clearing key. Answer repeat.-If an existing dialled call is broken due to a fault, the called station uses the calling stations address in origin store USn1 to cause central control to repeat the call setting up procedure. Special features. Conferences.-Either party of an existing connection causes a third station to be added by depressing a conference key and dialling or direct calling the third station. The third station is connected by the network ABC with the originally calling station of the existing connection no matter which of the existing stations calls the third station. Any station except the originally calling station can therefore withdraw from the conference without breaking the connection between the remaining two stations. Hence call transfer is accomplished. Priority break-in.-A station breaks into an existing connection if an emergency key is depressed before the number of required station is signalled. A speech path is then immediately set up irrespective of whether the called station is busy. A special signal may be sent to the called station if it is free to indicate an urgent call. This may be achieved by flashing a lamp associated with an origin store. This feature is not provided if there is a direct call key corresponding to the calling station. Interim calls.-Either stations in an existing connection may place the call on "hold" and make an interim call by depression of a hold key. A second depression of the key re-establishes the original connection. Calls to PBX and the public network.-Trunks QLp/R1, QLm/R2 extending to a PBX or other exchange have stores associated therewith and when a calling station dials an access code both the number of the calling and called stations are transferred to such a store. A connection is established between the calling station and the trunk when the external subscriber replies, in a similar manner to a dialled internal call.