Data Link Layer

  • Layer 2 in the Open Systems Interconnection Model

  • Transforms the physical layer, a raw transmission facility, to a link responsible for node-to-node (hop-to-hop) communication

Specific Responsibilities of the Data Link Layer

  1. Framing - It divides the stream of bits received from the network layer into manageable data units called frames.

  2. Addressing - It adds a header to the frame to define the addresses of the sender and receiver of the frame.

  3. Flow Control - If the rate at which the data are absorbed by the receiver is less than the rate at which data are produced in the sender, the data link layer imposes a flow control mechanism to avoid overwhelming the receiver.

  4. Error Control - It adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged, duplicate, or lost frames.

  5. Media Access Control - When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time.