Elements of a LAN
Ethernet-based LANs make up the heart of enterprise13 networks. A sample LAN is
depicted in Figure 1.3. LANs are often shown using a bus topology but star topologies
are frequently used in modern day LANs.
?– Data Terminating Equipment (DTE) These devices are either the source or
destinations for the data and include PCs, servers, printers, and so on.
?– Data Communication Equipment (DCE) These are the intermediate devices
that receive and forward Ethernet frames and include devices such as Ethernet
switches and routers as well as the NIC (integrated into the PCs and other devices).
11 Actually 4094 VIDs are usable; a VID of 0 identifies a priority frame and a VID of 4095 is reserved.
12 A technique called Q-in-Q, defined in IEEE 802. 1Q, allows the stacking of two VLAN tags (an enterprise
VLAN tag and a Service Provider??“added VLAN tag) to overcome this scaling limitation, so multiple
VLAN tags belonging to a specific customer can be mapped to one Service Provider tag.
13 Enterprise is used broadly to refer to the host of entities??”whether businesses, academia, or nonprofits??”
that have computer (or information technology) infrastructures.
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