|The simplest WLAN configuration is an independent LAN that connects a
set of PCs with wireless adapters. Any time two or more wireless adapters
are within range of each other, they can set up an independent network (Figure
3). These on-demand networks typically require no administration or
Access points can extend the range of ad hoc LANs by acting as a repeater,
effectively doubling the distance between wireless PCs.
Figure 4. Extended-Range Independent WLAN Using Access Point as Repeater
In infrastructure WLANs, multiple access points link the WLAN to the wired
network and allow users to efficiently share network resources. The access
points not only provide communication with the wired network but also mediate
wireless network traffic in the immediate neighborhood. Multiple access points
can provide wireless coverage for an entire building or campus.
Figure 5. Infrastructure WLAN
Microcells and Roaming
Wireless communication is limited by how far signals carry for given power
output. WLANs use cells, called microcells, similar to the cellular telephone
system to extend the range of wireless connectivity. At any point in time,
a mobile PC equipped with a WLAN adapter is associated with a single access
point and its microcell, or area of coverage. Individual microcells overlap
to allow continuous communication within wired network. They handle low-power
signals and "hand off" users as they roam through a given geographic area.
Figure 6. Handing off the WLAN Connection Between Access Points