The data link layer organizes communication over a link, typically using data-link frames and local checking or access rules.
Framing identifies the boundaries of data-link frames in a transmitted stream, allowing a receiver to locate separately interpretable link-level units.
Bit stuffing inserts extra bits according to an agreed rule, for example after five consecutive ones, so that a reserved frame delimiter cannot occur inside encoded contents. The receiver reverses the insertion rule.
A frame delimiter marks a data-link frame boundary. A transparency rule such as bit stuffing prevents data from accidentally imitating the reserved delimiter.
