A busy signal (or busy tone or engaged tone) in telephony is an audible or visual signal to the calling party that indicates failure to complete the requested connection of that particular telephone call.
There are several distinctly different types of busy signals:
- a reorder tone, (sometimes called a fast busy signal), indicates that no transmission 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.
Countries have different signaling tones that act as "busy signals", in most cases consisting of a tone with equal on/off periods at a rate of between 60 and 120 interruptions per minute.
In North America, the Precise Tone Plan used today employs two tones of 480 and 620 Hz at 60 i.p.m. (i.e. on for 0.5 sec., off for 0.5 sec.). In the past, before the adoption of the PreciseTone system, busy signal was generally composed of the same tone as dial tone in the central office in question, interrupted at the same rate.
In the United Kingdom, busy tone consists of a single 400 Hz tone with equal 0.375-sec. on/off periods. This tone was adopted in the mid to late 1960's and replaced the older busy tone which was the same 400 Hz signal but at half the interruption rate (i.e. 0.75 sec. on, 0.75 sec. off).
Famous quotes containing the words busy and/or signal:
“I do not weep at the world—I am too busy sharpening my oyster knife.”
—Zora Neale Hurston (1891–1960)
“Perhaps having built a barricade when you’re sixteen provides you with a sort of safety rail. If you’ve once taken part in building one, even inadvertently, doesn’t its usually latent image reappear like a warning signal whenever you’re tempted to join the police, or support any manifestation of Law and Order?”
—Jean Genet (1910–1986)