data link

The data link layer specifies how devices attached to the network gain access tot he various computing resources. this later packages data into frames that are to be sent out on the network. some error checking and retransmission responsibilities are built into the layer. it is responsible for providing error-free transfer of frames from one computer to another through the physical layer

think of the network as a highway. the data link layer is the entry ramp or toll booth by which you can gain access onto the highway. similar tot he traffic lights found at onromas for control of merging traffic, access methods are contained in the data link protocol definition to tell each node when it is its turn to transmit data.

the IEEE working in conjunction with ISO established the IEEE 802 specification series that divides this layer into two sub-layers



Logical Link Control (LLC) the LLC sub-layer provides software controls to manage mutiple protocols that are simultaneously accessing the network. the IEEE 802.2 acts like an umbrella protocol for the vairous MAC sublayer protocols.

Media Access Control (MAC) the MAC layer physically defines how devices control access to the network. this layer defines the network adapter inerface options, supported cable types and the designeated access methos. ther are number ot specifications defined, including 802.3 (CSMA/CD or Ethernet) 802.4 (Token Bus) and 802.5 (Token Ring)

Data Link	Logical Link Control LLC Layer	802.2 (LLC sublayer)
	Media Access Control MAC Layer	802.3 (Ethernet) 802.4 (Token Bus) 802.5 (Token Ring)
Physical Layer	Physical Layer

Devices Used in Layer 2:

Switch
Bridge
Nic Card
ISDN Card

examples:
ethernet
token ring
FDDI
SDLC