Bit Stuffing

Bit stuffing is a widely used process in network and communication protocols as a part of transmission process, also used while sending arbitrary data over a communications channel with bandwidth limits (sometime known as run-length limited (RLL)coding).

In communication, to separate one frame from another frame delimiters are used. For most protocols the delimiter usually a sequence of 8-bit pattern are used. In the bit oriented protocol the frame contains sequence of bits representing data. On receiving these frame the layer in the receiver interpret the data part of the frame into usual form. Sometimes the data part are misinterpreted by receiver for delimiter because same pattern used for delimiter may occur in data part. To overcome this, a single bit is stuffed into the data part of the frame to distinguish the delimiter separately. On reaching, receiver remove he stuffed bit from the data part in the frame. For instance if the pattern used for delimiter is 01111110 and in the data part if five consecutive 1 followed by a zero occurred an extra 0 bit is stuffed after fifth 1 into data which is removed by receiver. For example if the data part of the frame contains the following sequence 101111110101, then 0 is stuffed into it after five consecutive 1s, 1011111010101
Bit stuffing, technique is useful when communication protocol requires fixed frame size.

Bit stuffing used in run-length limited(RLL) coding, in which occurrence of same consecutive bits(on reaching allowed numbers) are limited by stuffing opposite bits in specific interval. RLL is a method used in PC Hard Disk,Floppy,CD,DVD for storing data/information. RLL method helps the hard disk to store data more densely than other method such as MFM (Modified Frequency Modulation) and FM(Frequency Modulation).