synchronise its clock against the transitions to ensure proper data recovery. In SDLC the transmitted bit sequence "01111110" containing six adjacent 1 bits is the Flag byte. Bit stuffing ensures that this pattern can never occur in normal data, so it can be used as a marker for the beginning and end of the frame without any possibility of being confused with normal data. The main disadvantage of bit-stuffing is that the code rate is unpredictable; it depends on the data being transmitted. Source: from Federal Standard 1037C in support of MIL-STD-188 See also Consistent Overhead Byte Stuffing Notes Line codes Synchronization