A stream of data in which the data arrives at a variable number of bits per second. For example, where data are to be transferred out of the memory of one computer system, across a network, and into the memory of a second computer system, it is perfectly feasible to suspend the transfer at some stage and to restart it later, without any detriment to the transfer. Such changes in the rate of delivery of data are not tolerable when transmitting digitally encoded speech. See also codec, constant bit rate.