Byte-oriented vs Bit-oriented protocols

Aspect	Byte-oriented protocol	Bit-oriented protocol
Unit of framing	Treats the frame as a sequence of bytes/characters	Treats the frame as a raw sequence of individual bits
Delimiters	Uses special reserved control bytes (e.g. flag byte, escape byte) to mark frame boundaries	Uses a specific bit pattern (e.g. 01111110) as the flag to mark frame boundaries
Data transparency technique	Byte stuffing	Bit stuffing
Examples	PPP, BISYNC	HDLC, SDLC
Overhead granularity	Overhead added/removed at byte level	Overhead added/removed at bit level, more flexible/fine-grained

Byte-stuffing vs Bit-stuffing

Aspect	Byte-stuffing	Bit-stuffing
What it protects against	Accidental occurrence of the flag byte (e.g. specific 8-bit pattern) inside the actual data payload	Accidental occurrence of the flag bit pattern (e.g. six consecutive 1s: 011111 10) inside the actual data payload
Mechanism	Whenever the flag byte (or the designated ESC byte itself) appears in the data, an extra ESC (escape) byte is inserted immediately before it. The receiver removes any ESC byte it finds and treats the following byte as literal data.	Whenever five consecutive 1s appear in the data, the sender inserts an extra 0 immediately after them. The receiver, upon seeing five consecutive 1s followed by a 0, removes that inserted 0.
Example	Data containing byte 01111110 (same as flag) → sender inserts ESC before it: ESC 01111110	Data 011111 1 (contains five 1s in a row) → sender inserts a 0: 0111110 1
Granularity	Operates at byte level (coarser)	Operates at bit level (finer, more precise, no wasted stuffing when only a few bits match)
Used with	Byte-oriented protocols	Bit-oriented protocols

In essence, both techniques serve the same purpose — preventing an accidental appearance of the frame delimiter pattern from being mistaken for an actual frame boundary — but operate at different granularities matching their respective protocol style.