The data link layer is concerned with local delivery of frames between nodes on the same level of the network.
Data-link frames, as these protocol data units are called, do not cross the boundaries of a local area network.
In this way, the data link layer is analogous to a neighborhood traffic cop; it endeavors to arbitrate between parties contending for access to a medium, without concern for their ultimate destination.
Data-link protocols specify how devices detect and recover from such collisions, and may provide mechanisms to reduce or prevent them.
In those cases, higher-level protocols must provide flow control, error checking, acknowledgments, and retransmission.
In the ITU-T G.hn standard, which provides a way to create a high-speed (up to 1 Gigabit/s) local area network using existing home wiring (power lines, phone lines and coaxial cables), the data link layer is divided into three sub-layers (application protocol convergence, logical link control and media access control).
[3] The uppermost sublayer, LLC, multiplexes protocols running at the top of the data link layer, and optionally provides flow control, acknowledgment, and error notification.
It specifies which mechanisms are to be used for addressing stations over the transmission medium and for controlling the data exchanged between the originator and recipient machines.
More advanced methods than parity error detection do exist providing higher grades of quality and features.
A simple example of how this works using metadata is transmitting the word "HELLO", by encoding each letter as its position in the alphabet.