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Logical Link Control (LLC)

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The Logical Link Control is an IEEE 802.x protocol loosely based on HDLC that provides the upper layer networking software (Novell IPX or Internet IP) access to the MAC sublayer and the unde rlying physical hardware.

LLC SUBLAYERS

The LLC is broken down into three componet sub-layers:

  • Destination Service Access Point (DSAP)
  • Source Service Access Point (SSAP)
  • Control (CTL)

THREE SERVICE TYPES

  • Unacknowledged Connectionless
  • Acknowledged Connectionless
  • Connection-Mode service

LLC OPERATION MODES

  • LLC 1 - Uses unnumberd PDU's for data transfer.
  • LLC 2 - Connection oriented, Uses HDLC Asynchronous Balanced Mode for transfer.
  • LLC 3 - Used for mainframe connectivity

Both types provide Service Access Points which allow the hardware and the networking software to communicate. LLC1 is the most common type however as it is used to transmit IP datagrams as well as ARP/RARP packets.

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