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:
“Living, just by itself—what a dirge that is! Life is a classroom and Boredom’s the usher, there all the time to spy on you; whatever happens, you’ve got to look as if you were awfully busy all the time doing something that’s terribly exciting—or he’ll come along and nibble your brain.”
—Louis-Ferdinand Céline (1894–1961)
“The experience of a sense of guilt for wrong-doing is necessary for the development of self-control. The guilt feelings will later serve as a warning signal which the child can produce himself when an impulse to repeat the naughty act comes over him. When the child can produce his on warning signals, independent of the actual presence of the adult, he is on the way to developing a conscience.”
—Selma H. Fraiberg (20th century)