The MAC-client sublayer may be one of the following:
� Logical
Link Control (LLC), if the unit is a DTE. This sublayer provides the interface
between the Ethernet MAC and the upper layers in the protocol stack of the end
station. The LLC sublayer is defined by IEEE 802.2 standards.
�Bridge
entity, if the unit is a DCE. Bridge entities provide LAN-to-LAN interfaces
between LANs that use the same protocol (for example, Ethernet to Ethernet) and
also between different protocols (for example, Ethernet to Token Ring). Bridge
entities are defined by IEEE 802.1 standards.
Because specifications for LLC and bridge entities are
common for all IEEE 802 LAN protocols, network compatibility becomes the primary
responsibility of the particular network protocol. Figure 7-5 shows different
compatibility requirements imposed by the MAC and physical levels for basic data
communication over an Ethernet link.
Figure 7-5 MAC and Physical Layer Compatibility
Requirements for Basic Data Communication
The MAC layer controls the node's access to the network
media and is specific to the individual protocol. All IEEE 802.3 MACs must meet
the same basic set of logical requirements, regardless of whether they include
one or more of the defined optional protocol extensions. The only requirement
for basic communication (communication that does not require optional protocol
extensions) between two network nodes is that both MACs must support the same
transmission rate.
The 802.3 physical layer is specific to the transmission
data rate, the signal encoding, and the type of media interconnecting the two
nodes. Gigabit Ethernet, for example, is defined to operate over either
twisted-pair or optical fiber cable, but each specific type of cable or
signal-encoding procedure requires a different physical layer implementation.
| 
