Bit stuffing does not ensure that the payload is intact ( " i . e . " not corrupted by transmission errors ); it is merely a way of attempting to ensure that the transmission starts and ends at the correct places.
12.
"' Flag "' The value of the flag is always 0x7E . In order to ensure that the bit pattern of the frame delimiter flag does not appear in the data field of the frame ( and therefore cause frame misalignment ), a technique known as Bit stuffing is used by both the transmitter and the receiver.
13.
However, even NRZI can have long series of zeros ( or ones if transitioning on " zero " ), and thus clock recovery can be difficult unless some form of run length limited ( RLL ) coding is used in addition to NRZI . Magnetic disk and tape storage devices generally use fixed-rate RLL codes, while USB uses bit stuffing, which inserts an additional 0 bit after 6 consecutive 1 bits, thus forcing a transition.
