What are the headers used in a Data Link Layer?

The Data Link Layer uses headers to control frame transmission and ensure reliable communication between directly connected nodes. These headers contain essential control information that enables proper frame delivery, sequencing, and error handling.

Data Link Layer Frame Structure

A frame is the unit of communication in the data link layer. The data link layer encapsulates packets from the Network Layer into frames, adding necessary control information through headers. If frames become too large, packets may be divided into smaller frames for efficient transmission.

Frame Header Components

The frame header contains addressing and control information essential for proper frame handling. It consists of destination address, source address, and control fields that manage frame transmission.

Control Fields in Frame Header

• Kind Field − Identifies the frame type, indicating whether it carries data or serves control functions like error handling, flow control, or link management.

• Sequence Field (seq) − Contains the sequence number for frame ordering, enabling the receiver to rearrange out-of-sequence frames and send proper acknowledgments.

• Acknowledgment Field (ack) − Carries acknowledgment numbers for received frames, particularly useful in piggybacking scenarios where data and acknowledgments are combined.

Header Types by Protocol

Frame Processing

At the sender, the data link layer adds headers containing control information and addresses. At the receiver, the layer processes header fields to determine frame type, check sequence numbers, and extract addressing information before passing data to the network layer.

Conclusion

Data Link Layer headers provide essential control and addressing information through kind, sequence, and acknowledgment fields. These headers enable reliable frame transmission, proper sequencing, and effective error and flow control between directly connected network nodes.