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In EU countries and those following ETSI (European Telecommunication Standards Institute) recommendations, the cadence is the same as North America, i.e. 0.25 seconds on / 0.25 seconds off, but with a 425 Hz tone. The UK reorder tone uses a 400 Hz tone with a cadence of 0.4 seconds on, 0.35 seconds off, 0.225 seconds on, 0.525 seconds off.
The tone frequencies, as defined by the precise tone plan, are selected such that harmonics and intermodulation products will not cause an unreliable signal. No frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the ...
Low tone, also busy tone, is defined as having frequency components of 480 and 620 Hz at a level of −24 dBm and a cadence of one half second ON and one half second OFF. Reorder tone, also often called fast busy tone, is the same tone, but with a cadence of 0.25 of a second ON and 0.25 of a second OFF. The original plan had two slightly ...
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.
In the United Kingdom, the busy tone is a single 400 Hz tone with equal 0.375 s on/off periods. This was the case even when the UK was still part of the EU. The current 400 Hz/375ms tone was adopted in the mid-to-late 1960s and replaced the older busy tone, which was the same 400 Hz signal but at half the pulse duration, 0.75 s on, 0.75 s off.
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 circuit; loud enough to be heard across a room from an unused off-hook telephone.
Multifrequency signaling is a technological precursor of dual-tone multi-frequency signaling (DTMF, Touch-Tone), which uses the same fundamental principle, but was used primarily for signaling address information and control signals from a user's telephone to the wire-center's Class-5 switch. DTMF uses a total of eight frequencies.
A signal tone or signalling tone is a steady or pulsating periodic signal typically in the frequency range of sound for indicating a condition, communication protocol state, or serve as an audible warning. It may be composed of multiple frequency components, or could be a pure tone.