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Phone Signalling: On Hook, Dial Tone, Pulse, DTMF

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Supervisory signalling, Information signalling or Address signalling, these are the groupings to define the various states, tones and methods to setup a phone call between parties.  The following is a quick reference for your viewing pleasure.

Please comment below with any suggestions (or further details on this topic).

Supervisory Signalling

  • On-Hook
  • Off-Hook
  • Ringing

Informational Signalling

North America uses a dual-frequency system to represent most of these signals/tones while in Europe a single frequency system is used.

  • Dial Tone

Event

Low frequency

High frequency

Dial tone (US)

350 Hz

440 Hz

Event

Low frequency

High frequency

Dial tone (UK)

350 Hz

450 Hz

  • Busy

Event

Low frequency

High frequency

Busy Signal (US)

480 Hz

620 Hz

Event

Low frequency

High frequency

Busy signal (Most of Europe)

425 Hz

—-


  • Ringback Tone

Event

Low frequency

High frequency

Ringback Tone (US)

440 Hz

480 Hz

Event

Low frequency

High frequency

Ringback Tone (Most of Europe)

425 Hz

—-

Event

Low frequency

High frequency

Ringback Tone (UK & Ireland)

400 Hz

450 Hz

  • Reorder
  • Receiver off Hook
  • Congestion
  • Confirmation
  • No such number

Address Signalling

Used to send dialing information over the analog line:

  • Pulse
  • DTMF
DTMF Frequencies

DTMF Frequencies Dialpad


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About Behzad Munir

Behzad Munir, P.Eng, is a Voice Solutions Consultant working in Toronto, Canada

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