What is the primary purpose of a Data Link Layer protocol?

The primary purpose of a Data Link Layer protocol is to transmit frames across a physical link. The Data Link Layer is responsible for node-to-node data transfer and provides the necessary framing, addressing, and error detection/correction mechanisms needed to ensure that data packets can be properly shared between devices over a network medium. This layer ensures that data is organized into frames, which includes not only the payload but also header information that indicates the source and destination addresses, along with control information like error detection codes.

This focus on framing and transmission distinguishes the Data Link Layer from other layers. For instance, while the Physical Layer deals strictly with the raw bits being sent over a medium, the Data Link Layer packages these bits into frames that enable more advanced networking features. The Data Link Layer also plays a crucial role in ensuring the reliability and proper sequencing of data frames as they traverse the physical medium.