Computer Networks Notes - CS Sem 5 Unit 2 Data Link Layer and MAC Sublayer

The network layer deals with packets, but the data link layer converts those packets into frames that can travel across one physical hop. It adds control information such as addresses, checks, and delimiters so communication on the local link becomes organized.

In exam answers, this topic scores better when written as a list of specific design goals. Framing, addressing, flow control, error control, and medium access are the most expected points.

Framing is important because the receiver must know where a frame starts and where it ends. This can be achieved through character count, byte stuffing, bit stuffing, or physical layer coding violations depending on the protocol design.

Flow control prevents a fast sender from overwhelming a slow receiver. Error control ensures lost, damaged, or duplicate frames can be detected and handled. On shared media, the MAC sublayer decides how multiple devices get a fair chance to transmit.