Busy signal
Encyclopedia
A busy signal in telephony is an audible or visual signal to the calling party
Calling party
The calling party is a person who initiates a telephone call over the public switched telephone network, usually by dialing a telephone number....

 that indicates failure to complete the requested connection
Telecommunication circuit
A telecommunication circuit is any line, conductor, or other conduit by which information is transmitted.A dedicated circuit, private circuit, or leased line is a line that is dedicated to only one use...

 of that particular telephone call
Telephone call
A telephone call is a connection over a telephone network between the calling party and the called party.-Information transmission:A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile...

.

There are several distinctly different types of busy signals:
  • a reorder tone
    Reorder tone
    The reorder tone, also known as the fast busy tone, is the congestion tone or all trunks busy tone of a public switched telephone network. It varies from country to country; in the USA it is a dual-frequency tone of 480 Hz and 620 Hz at a cadence of 0.25 seconds on, 0.25 off; that is two beeps per...

    , (sometimes called a fast busy signal), indicates that no transmission
    Transmission (telecommunications)
    Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...

     path to the called number is available;
  • an otherwise unspecified busy signal indicates that the called number is occupied or otherwise unavailable;
  • this tone sometimes occurs at the end of a call to indicate the other party has hung up. See disconnect supervision
    Disconnect supervision
    Disconnect supervision is a term in telephony describing signaling between the telephone exchange and a connected party used to indicate that the connected call is being disconnected....

    .


Many different countries have different signalling tones that act as "busy signals".

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