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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 .
An off-hook condition represents a circuit that is in use, e.g., when a telephone call is in progress. An on-hook condition represents an idle circuit, i.e. no telephone call is in progress. A central office originally was a primary exchange in a city with other exchanges service parts of the area.
The off-hook tone in exchanges of the North American Numbering Plan consists of a superposition of tones with the frequencies 1400 Hz, 2060 Hz, 2450 Hz, and 2600 Hz, played at a cadence of 100 ms on and 100 ms off. [1]
A dial tone (dialling tone in the UK) is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is working and is ready to initiate a telephone call. The tone stops when the first dialed digit is recognized.
Line signaling is concerned with conveying information on the state of the line or channel, such as on-hook, off-hook (answer supervision and disconnect supervision, together referred to as supervision), ringing, and hook flash. Register signaling is concerned with conveying addressing information, such as the calling and/or called telephone ...
The mechanisms described so far only allow circuit seizure – on-hook and off-hook – to be signaled. In order to allow dialing over the interface, "start" signaling mechanisms are defined. This allows the other end to know when to send the dialed digits, which are transmitted by pulse (loop disconnect) or multi-frequency tones. E&M defines ...
Permanent signal (PS) in American telephony terminology, or permanent loop in British usage, is a condition in which a POTS line is off-hook without connection for an extended period of time. [1] This is indicated in modern switches by the silent termination after the off-hook tone times out and the telephone exchange computer puts the ...
"This is a recording. Please hang up. There appears to be a receiver off the hook. Please check your main telephone and extensions, then try your call again. Thank you." The message may be repeated, then followed by a loud, rasping off-hook tone intended to remain audible even if the handset is on the desktop instead of at the subscriber's ear ...