bit stuffing

protocol A protocol which guarantees the receiver of

synchronous data can recover the sender's clock. When the

data stream sent contains a large number of adjacent bits

which cause no transition of the signal, the receiver cannot

adjust its clock to maintain proper synchronised reception.

To eliminate the possibility of such a pathological case, when

a preset number of transitionless bits have been transmitted,

a bit which does cause a transition is "stuffed" (transmitted)

by the sender. The receiver follows the same protocol and

removes the stuffed bit after the specified number of

transitionless bits, but can use the stuffed bit to recover

the sender's clock.

The advantage of bit stuffing is that only a bit (not a

byte) is inserted in the data stream, and that only when the

content of the data stream fails to provide a timing signal to

the receiver. Thus very nearly 100% of the bits transported

are useful data. In contrast, asynchronous transmission of

data "throws away" a start bit and one or more stop bits for

each data byte sent.

(1996-04-23)