Data-Link Layer

The data-link layer provides error-free transfer of data frames from one computer to another over the physical layer. The layers above this layer can assume virtually error-free transmission over the network.

The data-link layer provides the following functions:

• Establishment and termination of logical links (virtual-circuit connection) between two computers identified by their unique network adapter addresses.

• Control of frame flow by instructing the transmitting computer not to transmit frame buffers.

• Sequential transmission and reception of frames.

• Providing and listening for frame acknowledgment, and detecting and recovering from errors that occur in the physical layer by retransmitting non-acknowledged frames and handling duplicate frame receipts.

• Management of media access to determine when the computer is permitted to use the physical medium.

• Delimiting of frames to create and recognize frame boundaries.

• Error-checking of frames to confirm the integrity of the received frame.

• Inspection of the destination address of each received frame and determination of whether the frame should be directed to the layer above.

Note

While the services of the data-link layer provide for reliable delivery of data, many routable protocol suites such as TCP/IP and IPX/SPX do not provide for, nor utilize reliable data-link layer delivery services. Instead, reliable data delivery is provided by protocols operating at the transport layer.