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constant bit rate (CBR) A stream of data in which the data arrives at a fixed number of bits per second. The term may also imply that there is a guaranteed upper bound on the delay experienced by the data as it is carried. As an example, a speech codec generates an 8-bit byte at intervals of 125 microseconds; each byte contains the result of sampling an audio signal, and digitizing it as an 8-bit quantity, and the result is a signal with a bandwidth requirement of 64 Kbps. If during transmission any of the samples are lost or delayed, then the reconstructed speech signal may well be unintelligible as the human ear is very intolerant of gaps in speech. It is therefore essential to guarantee that the full 64 Kbps can always be carried, and that the transmission delay will be effectively constant. See also bounded delay, network delay, variable bit rate.

constant bit rate

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