Local Area Network (LAN)

A network covering a small geographic area, like a home, office, or
building. Current LANs are most likely to be based on Ethernet
technology. For example, a library may have a wired or wireless LAN
for users to interconnect local devices (e.g., printers and servers)
and to connect to the internet. On a wired LAN, PCs in the library are
typically connected by category 5 (Cat5) cable, running the IEEE 802.3
protocol through a system of interconnection devices and eventually
connect to the internet. The cables to the servers are typically on
Cat 5e enhanced cable, which will support IEEE 802.3 at 1 Gbit/s. A
wireless LAN may exist using a different IEEE protocol, 802.11b or
802.11g. The staff computers (bright green in the figure) can get to
the color printer, checkout records, and the academic network and the
Internet. All user computers can get to the Internet and the card
catalog. Each workgroup can get to its local printer. Note that the
printers are not accessible from outside their workgroup.

All interconnected devices must understand the network layer (layer
3), because they are handling multiple subnets (the different colors).
Those inside the library, which have only 10/100 Mbit/s Ethernet
connections to the user device and a Gigabit Ethernet connection to
the central router, could be called "layer 3 switches" because they
only have Ethernet interfaces and must understand IP. It would be more
correct to call them access routers, where the router at the top is a
distribution router that connects to the Internet and academic
networks' customer access routers.

The defining characteristics of LANs, in contrast to WANs (wide area
networks), include their higher data transfer rates, smaller
geographic range, and lack of a need for leased telecommunication
lines. Current Ethernet or other IEEE 802.3 LAN technologies operate
at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has
projects investigating the standardization of 100 Gbit/s, and possibly
40 Gbit/s.