A ringback tone (or ringing tone) is an audible indication that is heard on the telephone line by the caller while the phone they are calling is being rung. It is normally a repeated tone, designed to assure the calling party that the called party's line is ringing, although the ring-back tone may be out of sync with the ringing signal.
The ringback tone (or "RBT") is in most cases generated in the distant switch and transmitted in-band. A message is also sent over the signaling system (usually SS7). In most public phone networks the tone is not generated in the handset or by the local switch, as customized tones or voice announcements may be generated by the distant switch in place of a ringing signal.
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Famous quotes containing the word tone:
“If the oarsmen of a fast-moving ship suddenly cease to row, the suspension of the driving force of the oars doesn’t prevent the vessel from continuing to move on its course. And with a speech it is much the same. After he has finished reciting the document, the speaker will still be able to maintain the same tone without a break, borrowing its momentum and impulse from the passage he has just read out.”
—Marcus Tullius Cicero (106–43 B.C)