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In telephony, the term off-hook has the following meanings: # The condition that exists when a telephone or other user instrument is in use, ''i.e.'', during dialing or communicating. # One of two possible signaling states, such as tone or no tone and ground connection versus battery connection. Note that if off-hook pertains to one state, on-hook pertains to the other. # The active state (''i.e.'', a closed loop (short circuit between the wires) of a subscriber line or PBX user loop) # An operating state of a communications link in which data transmission is enabled either for (a) voice or data communications or (b) network signaling.〔Federal Standard 1037C〕〔MIL-STD-188〕 On an ordinary two-wire telephone line, off-hook status is communicated to the telephone exchange by a resistance short across the pair. When an off-hook condition persists without dialing, for example because the handset has fallen off or the cable has been flooded, it is treated as a ''permanent loop'' or permanent signal. The act of ''going off-hook'' is also referred to as ''seizing'' the line or channel. ==Etymology== Off-hook originally referred to the condition that prevailed when telephones had a separate earpiece (''i.e.'', receiver), which hung from its switchhook until the user wished to activate it. The weight of the receiver no longer depresses the spring-loaded switchhook, thereby connecting the instrument to the telephone line. ==See also== *Hook flash *Line signaling *Off-hook tone 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「Off-hook」の詳細全文を読む スポンサード リンク
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