Signal tone

A signal tone or signalling tone (or signaling tone) is a steady or pulsating periodic sound (not necessarily a pure tone) used to indicate a condition, for example on a telephone line or as an audible warning.

In telephone systems, signaling tones are used as call progress tones for in-band indications to subscribers. Certain telephone switching systems used tones, in-band or out-of-band, for signaling on trunks.

Typical well-known call progress tones are dial tone, ringing tone, busy tone, and the reorder tone.[1] A loud stutter tone is used to alert subscribers of a handset left off-hook, effectively disabling the circuit for receiving calls.

Subscribers may choose to subscribe to additional services, such as call forwarding, which may indicate function by a stutter dial tone.

See also

References
  1. V. S. Bagad and I. A. Dhotre (2009). Data Communication Systems. Technical Publications. p. 8. ISBN 978-81-8431-698-8.
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