What is the function of the Data Link Layer of the OSI model?

The Data Link Layer defines how the signal will be placed on or taken off the NIC. It is here that the data frames are broken down into individual bits that can be translated into electronic signals and sent over the network. On the receiving side, the bits are reassembled into frames for processing by upper levels.

Error detection and correction is also performed at the data link layer. If an acknowledgement is expected and not received, the frame will be resent. Corrupt data is also identified at the data link layer.

Because the Data-Link Layer is very complex, it is sometimes divided into sublayers (as defined by the IEEE 802 model). The lower sublayer, called the MAC sublayer, provides network access. The upper sublayer, called the LLC sublayer, is concerned with sending and receiving packets and error checking.