词条 | On- and Off-hook |
释义 |
In telephony, on-hook and off-hook refer to the two possible states of a receiver. 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. Off-hookThe term off-hook has the following meanings:
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. On-hookThe term on-hook has the following meanings:
The act of going on-hook is also referred to as releasing the line or channel, and may initiate the process of clearing. See also
References{{FS1037C MS188}}1. ^{{cite web | url = https://archive.org/stream/bitsavers_westernEleEngineeringandOperationsintheBellSystem2_49741719/Engineering_and_Operations_in_the_Bell_System_2ed_1984 | title = Engineering and Operations in the Bell System, 2nd Ed | last = Rey | first = R. F. | date = 1984 | publisher = Bell Telephone Laboratories | access-date = 19 March 2017 | page = 267}} {{telephony-stub}}2. ^Federal Standard 1037C 3. ^MIL-STD-188 1 : Telephony signals |
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