LLC is a software component that provides a uniform interface to the user of the data link service, usually the network layer.
The IEEE 802.2 sublayer adds some control information to the message created by the upper layer and passed to the LLC for transmission to another node on the same data link.
Each network node is assigned an LLC Class according to which service types it supports: Any 802.2 LLC PDU has the following format: When Subnetwork Access Protocol (SNAP) extension is used, it is located at the start of the Information field: The 802.2 header includes two eight-bit address fields, called service access points (SAP) or collectively LSAP in the OSI terminology: Although the LSAP fields are 8 bits long, the low-order bit is reserved for special purposes, leaving only 128 values available for most purposes.
The SNAP extension allows using EtherType values or private protocol ID spaces in all IEEE 802 networks.
Instead, the Internet standard RFC 1042 is usually used for encapsulating IPv4 traffic in 802.2 LLC frames with SNAP headers on FDDI and on IEEE 802 networks other than Ethernet.
IEEE 802.2 was conceptually derived from HDLC, and has the same three types of PDUs: To carry data in the most-often used unacknowledged connectionless mode the U-format is used.