The Data Link Layer

   Data Link Layer Protocols

There are many different Data Link Layer protocols. Some of the most common are:

High-Level Data Link Control (HDLC), an ISO standard, and subsets of HDLC, such as:

  • Synchronous Data Link Control (SDLC), an IBM protocol

  • Link Access Procedure for D Channel (LAPD), used in Integrated
         Services Digital Networks (ISDNs)

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    LAN protocols, such as Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI).

    Wide area network (WAN) protocols, such as frame relay and ISDN.

    Two peer processes must use the same protocol to communicate. For example, communication at the Data Link Layer is not possible if the node at one end of a link uses the Ethernet protocol, while the node at the other end uses the frame relay protocol.