Data Transparency and Bit Stuffing
It refers to the ability to include arbitrary bit patterns in the data field of a frame without any pattern being confused with part of the control information in the frame.
Bit stuffing is used to avoid the appearance of flag-bit pattern elsewhere within the frame. For this transmitter always inserts an extra 0 bit after each occurrence of five 1’s within the frame. The receiver after getting the frame monitors the bitstream. When a pattern of five 1’s appears, the sixth bit is examined. If it is 0, it is deleted. If it is 1 then the seventh bit is examined. If it is 0 then it is detected as a flag and if it is then the sender is indicating abort condition.
The pitfall of bit stuffing is that it can combine two frames into one or it can split one frame into two or more parts. With the use of bit stuffing, an arbitrary bit pattern can be inserted into the data field of the frame. This property is known as Data Transparency.