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In landline telephony, a plant test number or exchange is a number or group of numbers reserved for use by telephone installers to perform routine tests on an individual telephone line. These include, but are not limited to: * Automatic number announcement circuit, a machine which announces the caller's own number〔http://www.artofhacking.com/tucops/phreak/callerid/live/aoh_anac.htm〕 * Loop around, a primitive conference call bridge〔http://home.ptd.net/~n3cvj/looplines.htm〕 * Milliwatt test, a standardised 1004 Hz, zero dBm sinusoidal test tone used to measure line quality and transmission loss between stations. * Ringback number, which causes the calling telephone to ring to verify an installation is working and the phone number routing properly. Each country uses different codes. BT Linetest Facilities (for example) are available by ringing 17070〔http://www.howtofixanything.co.uk/howto-btlinetestfacility.html〕 and a self-service test facility for subscribers is on 0800 800628.〔http://www.redcare.bt.com/PDF/Installations_Support/Self%20Service%20Line%20Test%20V1.pdf〕 In the North American Numbering Plan, 958-xxxx and +1-NPA-959-xxxx are commonly reserved for local and long-distance test numbers (respectively). A few localities (including Winnipeg) reserve 959 only.〔Plant test exchange prefixes appear in the list of CO Code assignments (per area code) at http://nanpa.com (US) and http://cnac.ca (Canada) but the individual numbers are unpublished by design, as they're intended for installers only.〕 ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Plant test number」の詳細全文を読む スポンサード リンク
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