Patent GB-1352238-A (GB)
Title: Control arrangement for private line communication system
IPC: H04M1/70
Filed: 1971-09-30
Abstract: 1352238 Telephone systems WESTERN ELECTRIC CO Inc 30 Sept 1971 [5 Oct 1970] 45486/71 Heading H4K A control arrangement for establishing selected connections between stations in a private line communication system comprises means for detecting an off-hook condition of a first calling one of the said stations and means responsive to said detection to exclusively extend signalling capability and bidirectional communication capability to said calling station. As shown the stations are arranged in groups each controlled by a location control circuit LCC-1 to LCC-n, the groups and their control circuits being spaced along a 4 wire transmission path. Associated with each station is a data set such as 216 which may be used to transmit data to similar sets associated with other stations to which a telephone connection has been made. To initiate a call a station handset is lifted and a button depressed. If no other handset in the system is off-hook a bi-stable in each of the location circuits will have been reset and the station transmitter, dial mechanism and the station receiver are coupled to the transmission path by the associated location control circuit which transmits a tone to the other location control circuits to inhibit similar action thereat and reverses the polarity of the supply to enable the dial mechanism of the off-hook station. From this point no other station can originate a call until the off-hook station handset is replaced. A three digit frequency or dial pulse code number of a wanted station, a number common to a plurality of stations, or a plurality of such numbers in succession are dialled and transmitted to each location circuit LC1. Each location circuit LC1 is adapted to detect the codes associated with the stations it controls and in response to such detection couples that or those stations to the transmission path. If a special code signifying that data transmission is to be effected is dialled the location control circuits couple up the associated data sets to the transmission path. If during a non-data call a further station handset is lifted the associated location control circuit causes an intermittent busy tone to be transmitted to the station. If a priority key at the station is now depressed the busy tone in continuous form is coupled to the transmission path to warn parties in the existing call that a priority call is required and that the call is no longer an exclusive one, and the station at which the priority key was depressed is coupled to the path so that priority caller can speak to the engaged parties. The priority caller cannot become the originating station and thus cannot make his call until all station handsets have been returned to the on-hook condition. During a data call busy tone is not returned to a further station that goes off hook. The receiver only of that station is coupled to the path to allow the caller to hear the data being transmitted. This avoids interference with data transmission. Stations may also be provided with emergency keys in response to operation of which the associated location control circuit causes a disconnect tone to be transmitted throughout the system to reset the bi-stable mentioned above. The system is thus cleared for the origination of the emergency call.