In telecoms it's always bits.
There are several reasons, but one is that you can't be certain that 8 consecutive bits belong together to make a byte, or that the bits will be assembled into bytes at all - the concept of a byte of data transmitted across a system exists at a different layer to the transmission mechanisms of that system.
In computing 'B' is bytes, 'b' is bits.
Biting the hand that feeds IT
