Local Area Networks

Local Area Networks

As with WANs, a LAN is a communications network that interconnects a variety of
devices and provides a means for information exchange among those devices. There
are several key distinctions between LANs and WANs:
1. The scope of the LAN is small, typically a single building or a cluster of buildings.
This difference in geographic scope leads to different technical solutions.
2. It is usually the case that the LAN is owned by the same organization that owns
the attached devices. For WANs, this is less often the case, or at least a significant
fraction of the network assets are not owned. This has two implications. First, care
must be taken in the choice of LAN, since there may be a substantial capital
investment (compared with dial-up or leased charges for WANs) for both purchase
and maintenance. Second, the network management responsibility for a
LAN falls solely on the user.
3. The internal data rates of LANs are typically much greater than those ofWANs.
A simple example of a LAN that highlights some of its characteristics is shown
in Figure 3.2. All of the devices are attached to a shared transmission medium. A
transmission from anyone device can be received by all other devices attached to
the same network.
Traditional LANs have provided data rates in a range from about 1 to 20 Mbps.
These data rates, though substantial, have become increasingly inadequate with the
proliferation of devices, the growth in multimedia applications, and the increased use
of the client/server architecture. As a result, much of the effort in LAN development
has been in the development of high-speed LANs, with data rates of 100 Mbps to
10 Gbps.