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:
“It hurts me to hear the tone in which the poor are condemned as “shiftless,” or “having a pauper spirit,” just as it would if a crowd mocked at a child for its weakness, or laughed at a lame man because he could not run, or a blind man because he stumbled.”
—Albion Fellows Bacon (1865–1933)