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British telephone sockets were introduced in their current plug and socket form on 19 November 1981 by British Telecom to allow subscribers to connect their own telephones. The connectors are specified in British Standard BS 6312.〔BS 6312-1:1994. Connectors for analogue telecommunication interfaces. Specification for plugs.〕〔BS 6312-2.1:1994. Connectors for analogue telecommunication interfaces. Sockets for use with plugs specified in BS 6312:Part 1. Specification for sockets. General requirements.〕〔BS 6312-2.2:1997. Connectors for analogue telecommunication interfaces. Sockets for use with plugs specified in BS 6312-1. Particular requirements for fixed socket-outlets used in permanent wiring installations.〕 Electrical characteristics of the telephone interface are specified by individual network operators,〔(Publication of Customer Interface Specifications ), Ofcom.〕 e.g. in British Telecom's SIN 351.〔(BT Public Switched Telephone Network (PSTN): technical characteristics of the single analogue line interface ), British Telecom, Suppliers Information Note SIN 351, Issue 4.5, May 2006.〕 Electrical characteristics required of British telephones used to be specified in BS 6305.〔BS 6305:1992. Specification for general requirements for apparatus for connection to public switched telephone networks run by certain public telecommunication operators. (obsolescent)〕 They are similar to modular connectors (as used in RJ11), but feature a side-mounted hook, rather than a bottom-mounted one, and are physically incompatible. ==History== Standard sockets were introduced, as part of the 'New Plan' wiring policy, to allow customers to easily purchase their own telephones, as required by Oftel, the phone regulator. Thus any phone whose plug conformed to BS 6312 and met certain other regulatory standards, such as BABT, could be connected to the network, rather than British Telecom controlling the market. The 'New Plan' was only new to the UK and was based extensively on systems which had been available elsewhere for many years, especially in the US. The new system replaced the older hard-wired system, which came in many 'flavours', e.g. Plans 1, 1A, 1B, 1C, 2, 2A, 105, 107 etc., which could be very complicated and required the attendance at the premises of a GPO telephone-engineer, who needed a complete set of 'N' (wiring) Diagrams, which was very extensive and ran to over 15 volumes of little black ring binders. N diagrams also had their own numbering system e.g. a Plan 1A had an N diagram of N4502, and were frequently updated. From the early years of the 1900s, the GPO (subsequently British Telecom) did have a plug and socket system available for rent (see Plate 3 in the 1909 edition of the Post Office Telegraphs "Connections of Telephonic Apparatus and Circuits" 1909 edition). It was later called a "Plan 4" (N762—first edition), and employed a heavy-duty, four-way jack plug 404 (circular in cross-section), on the end of the standard, plaited, cotton-covered instrument cord. It also had to have a separate bell-set, which was permanently in-circuit to provide ringing if there were no telephones plugged in. This system survived through various models of telephones from the "candlestick" 200 and 300 type bakelite phones until the introduction of the 700 series in 1959, when a smaller "Plug 420" was introduced. The separate bell-set, with its on-board capacitor and coils, also provided a testing circuit for remote engineers, by providing the mandatory 1000 ohm capacitive loop-back. Rental had to be paid on each telephone and on all the sockets, and hence the system was not that common. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「British telephone sockets」の詳細全文を読む スポンサード リンク
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