Media Access Control (MAC): Defines how packets are placed on the media. Contention for media access is “First come/first served” access where everyone shares the same bandwidth-hence the name. Physical addressing is defined here as well as logical topologies. Line discipline, error notification (not correction), the ordered delivery of frames, and optional flow control can also be used at this sub-layer.
Logical Link Control (LLC): Responsible for identifying network layer protocols and then encapsulating them. An LLC header tells the Data Link layer what to do with a packet once a frame is received. It works like this: a host receives a frame and looks in the LLC header to find out where the packet is destined-for instance, the IP protocol at the network layer. The LLC can also provide flow control and sequencing of control bits.
Todd Lammle
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