GB1376683A - Vf keying systems - Google Patents

Abstract

1376683 Automatic exchange systems INTERNATIONAL STANDARD ELECTRIC CORP 28 Sept 1971 [2 Oct 1971] 44781/72 Heading H4K In a telecommunication system in which a call trace circuit is arranged to supervise at least one subscriber station, to respond to a call trace request tone signal from such a station and to prevent that signal from reaching a calling station, means is provided to respond to a different tone signal from such a station and to open the transmission path between the subscribers to data signals of audio frequency form. As described the call trace circuit is additionally adapted to receive call trace request signals and transmission path opening requests from dial pulse subscribers. The call trace junctor FVS shown can be associated with a subscriber station on a semi-permanent basis or may be taken into use when the class of service of that station so indicates and that station is being called. The junctors can be generally as described in Specifications 1,094,277 or 1,142,740 and include a supply element SpG, a hybrid G, a circuit Sp including a narrow band filter for preventing the passage of a call trace request tone originated from a called subscriber with a push-button multi-frequency sender from reaching the calling subscriber and a gate arrangement for this purpose in the case of a called subscriber with a dial pulse substation, and receivers IWE and TWE for receiving dial pulse and multi-frequency signals respectively and for operating call trace or switch through relays F or D depending on the particular code received from the called station Tln. The relay D if operated changes over contacts d from the positions shown to allow voice frequency data signals free passage between the subscribers. A centrally controlled system in which an intercept junctor, initially taken into use on a subscriber being called, is released and replaced by a conventional junctor, on detection of the said different signal is also outlined.