The off-hook tone (also off-hook warning, howling tone, or howler tone) is a
telephony signal
In telecommunication, signaling is the use of signals for controlling communications. This may constitute an information exchange concerning the establishment and control of a telecommunication circuit and the management of the network.
Classif ...
for alerting a user that the
telephone has been left
off-hook without use for an extended period, effectively disabling the
telephone line.
North America
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 hertz
2600 hertz (2600 Hz) is a frequency in hertz (cycles per second) that was used by AT&T as a steady signal to mark currently unused long-distance telephone lines.
During the 1960s, in-band signaling was used, so the same line for both voi ...
, played at a
cadence of on and off.
Telcordia GR-506-CORE Issue 3 December 2011, ''Signaling for Analog Interfaces''
Section 17.2.8 ''Receiver-Off-Hook (ROH) Tone'' The signal is applied to the local loop by the switching system for permanent signal treatment to alert an end user (subscriber) of an off-hook condition of the telephone set, i.e. that the telephone handset should be placed on-hook.
Before playing the signal, a certain timeout has to elapse, and on some systems an intercept message is announced (e.g. "If you'd like to make a call, please hang up and try again. If you need help, hang up and then dial your operator. This is a recording.").
A single burst of off-hook tone is sometimes used to indicate to a party that the call is being transferred, notably at 1-800- BELL-SOUTH (800-235-5768).
Some central office switches in the United States, notably older GTD-5 EAX systems, utilize a single frequency tone, 480 Hz, known as ''High Tone'' for this purpose. In either case, the tone is substantially louder than any other signal transmitted over a copper POTS
Pot may refer to:
Containers
* Flowerpot, a container in which plants are cultivated
* Pottery, ceramic ware made by potters
* A type of cookware
Places
* Ken Jones Aerodrome, IATA airport code POT
* Palestinian Occupied Territories, the We ...
circuit; loud enough to be heard across a room from an unused off-hook telephone.
HOWLER
In the United Kingdom, a warbling signal sounding rather like an alarm siren is played at steadily increasing volume to a telephone left off-hook and unused on telephone lines provided by the BT Group and many PABX extensions. It is sometimes referred to as a ''howler.''
In some cases it is composed of the DTMF tones * and # played alternately.
Telephone lines provided by NTL/ Virgin Media tend to use the American-style tones, including a recorded message.
See also
*
References
External links
High Tone
Telephony signals
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