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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

3 comments
Robbie Cain
Robbie Cain

  What kind of TOH tone was that? What was the technical name for that ROH tone? Please let me know. Thank you.

Robbie Cain
Robbie Cain

   There was a tone like that in the U.S. in Concord/Farragut Tn. with this phone company called Concord Telephone Exchange Inc. Now when I saw on Telco.us that concord Telephone Exchange Inc. had switches called AT&T/Philips Tel 5ESS-PBX Host and I saw something that said there were several switches called AT&T/Philips Tel 5ESS-PBX Host.

Robbie Cain
Robbie Cain

  Was there an off hook tone that was a medium pitch single tone that was with this telephone switch type called AT&T/Philips Tel 5ESS-PBX Host that the pitch wound up like a siren until it reached medium pitch and stayed at a steady medium pitch sound that went like a horn?

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