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Since most corporate WLANs require access to the wired LAN for services
(file servers, printers, Inter-net links) they will operate in infrastructure mode.
¦ 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.
The 802.11 MAC layer is responsible for how a client associates with an access point.
When an 802.11 client enters the range of one or more APs, it chooses an access point
to associate with (also called joining a Basic Service Set), based on signal strength and
observed packet error rates. Once accepted by the access point, th e client tunes to the
radio channel to which the access point is set. Periodically it surveys all 802.11 channels
Distribution System (DS)
Ethernet (802.3)
Access Point (AP)
Service Set (SS) – Multiple
Figure 2. Infrastructure Mode
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