Logical Link Control (LLC)

Logical Link Control (LLC) is one of two Data Link Layer (DLL) network protocol sublayers within the Open System Interconnection (OSI) data communication model. LLC is located in the upper DLL area of OSI Layer 2 above the Physical Layer (PHY) of OSI Layer 1.

LLC is standardized as IEEE 802.2 by the Institute of Electrical and Electronics Engineers (IEEE).

The LLC multiplexing interface includes the following network protocol features:

• Multipoint network operation
• Unified network media exchange
• Flow control
  
• Line protocol identification, like Synchronous Data Link Control (SDLC)
• Frame sequence number assignment
• Acknowledgement tracking

Today, LLC is only used for its multiplexing feature. Modern Transport Layer protocols, like TCP or other application layer protocols, are used for source and destination network flow management.

A non-IEEE 802 protocol may be distributed between the LLC and Media Access Control (MAC) layers, like Cisco’s High-Level Data Link Control (HDLC).