Editing Bit stuffing (section)

{{Short description|Practice in data transfers}}
{{Use American English|date = March 2019}}
{{no footnotes|date=March 2013}}

In [[data transmission]] and [[telecommunications]], '''bit stuffing''' (also known—uncommonly—as '''positive justification''') is the insertion of non-information [[binary digit|bits]] into [[data]]. Stuffed bits should not be confused with [[overhead bit]]s.

Bit stuffing is used for various purposes, such as for bringing [[bit stream]]s that do not necessarily have the same or rationally related [[bit rate]]s up to a common rate, or to fill [[Buffer (telecommunication)|buffers]] or [[Data frame|frames]]. The location of the stuffing bits is communicated to the receiving end of the [[data link]], where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before [[multiplexing]] or to rate-match two single channels to each other.

Another use of bit stuffing is for [[run length limited]] coding: to limit the number of consecutive bits of the same value in the data to be transmitted. A bit of the opposite value is inserted after the maximum allowed number of consecutive bits. Since this is a general rule the receiver doesn't need extra information about the location of the stuffing bits in order to do the de-stuffing. This is done to create additional signal transitions to ensure reliable reception or to escape special reserved code words such as frame [[sync sequence]]s when the data happens to contain them.
[[File:Bitstuffing en.svg|thumb|Bit stuffing in CAN after five equal bits]]

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. [[Error detection and correction]] techniques are used to check the frame for corruption after its delivery and, if necessary, the frame will be re-sent.