Bit stuffing

When bit stuffing (English bit stuffing ) is called in communication engineering inserting one or more filler bits in a data transfer to (ie no data in the proper sense / no payload data ) to transmit signal information to the recipient. The receiver needs to know how to recognize these additional bits inserted and removed again in order to obtain the actual user data in this case.

A possible example is the block structure of HDLC.

Bit stuffing in CAN

The method is also used for CAN. To allow synchronization of the participants should be prevented from a long monotonic sequences are transmitted from 0 or 1. This is to prevent the transmission between transmitter and receiver is drifting apart ( eg, due to some inaccurate clock signals between the participating ICs or communication participants).

When an inverse bit stuffing bit is inserted after five equal bits, and thereby a monotonic sequence is interrupted. The receiver knows this process and removed when receiving a sequence of five identical bits following the sixth bit and preserves the original data. As another possibility, the sixth bit may be examined. If you think it at that against the rules of the bit stuffing, then a transmission errors are detected.

Bit stuffing in the Ethernet

When bit stuffing in Ethernet, a zero is inserted only after 5 ones. A sequence of zeros does not matter. One exception is the order of 01111110 which indicates the end and the beginning. Bit stuffing is used in Ethernet to avoid bit sequences that may be interpreted in the data field of a frame as a control character.