Logical Link Control (LLC) is the upper portion of the data link layer of a local area network, as defined in IEEE 802.2. The LLC sublayer presents a uniform interface to the user of the data link service, usually the network layer. Beneath the LLC sublayer is the Media Access Control (MAC) sublayer. The IEEE standard adds this sublayer which adds the standard 8-bit DSAP (Destination Service Access Point) and SSAP (Source Service Access Point) labels to a given IP packet regardless of network type. There is also an 8 or 16 bit control field for use in auxiliary functions such as flow control.

The SAP labels identify the protocol stack that is sending the encapsulated data, and the protocol stack which the encapsulated data are for. The LLC also encapsulates the packet in its own protocol data unit (PDU). The MAC layer adds further data and encapsulates it in its own way. The frame is the end PDU of the data link layer, which is the second layer of the OSI model. This may help illuminate its purpose. As part of the encapsulation chain the LLC is used to enable layer 2 to talk to the higher layers in a standardized way, regardless of which lower-level technology is used. (Examples of such lower-level technologies are Token Ring, Ethernet, FDDI or ATM).