Call-progress tone

In telephony, call progress tones are audible tones sent from the public switched telephone network (PSTN) central office or a private branch exchange (PBX) to calling parties to indicate the status of phone calls.

Equipment such as fax machines and modems are designed to recognise dial tones and busy tones.

The ITU-T E.180 and E.182 recommendations define the technical characteristics and intended usage of some of these tones. ToneScript is a tone description format that may be used to specify the tone.

Types

Major ones encountered by the public on a regular basis are listed in bold:

• busy tone or busy signal
• call waiting tone
• comfort tone
• conference call tone
• confirmation tone
• congestion tone
• dial tone
• end of three-party service tone (three-way calling)
• executive override tone
• holding tone
• howler tone
• intercept tone
• intrusion tone
• line lock-out tone
• negative indication tone
• notify tone
• number unobtainable tone
• pay tone
• payphone recognition tone
• permanent signal tone
• preemption tone
• queue tone
• recall dial tone
• record tone
• recorder warning tone
• ringback tone or ringing tone
• ringtone or ringing signal
• second dial tone
• special dial tone
• special information tone (SIT)
• stutter dial tone (used as a message-waiting indicator)
• waiting tone

External links

• Various Tones Used in National Networks (According to ITU-T Recommendation E.180)