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Appendix B
About Wireless LANs
This Appendix provides some background information about using Wireless
LANs (WLANs).
Modes
Wireless LANs can work in either of two (2) modes:
•
Ad-hoc
•
Infrastructure
Ad-hoc Mode
Ad-hoc mode does not require an Access Point or a wired (Ethernet) LAN. Wireless Sta-
tions (e.g. notebook PCs with wireless cards) communicate directly with each other.
Infrastructure Mode
In Infrastructure Mode, one or more Access Points are used to connect Wireless Stations
(e.g. Notebook PCs with wireless cards) to a wired (Ethernet) LAN. The Wireless Stations
can then access all LAN resources.
Access Points can only function in "Infrastructure" mode,
and can communicate only with Wireless Stations which are
set to "Infrastructure" mode.
BSS/ESS
BSS
A group of Wireless Stations and a single Access Point, all using the same ID (SSID), form a
Basic Service Set (BSS).
Using the same SSID is essential . Devices with different SSIDs are unable to communicate
with each other.
ESS
A group of Wireless Stations, and multiple Access Points, all using the same ID (ESSID), form
an Extended Service Set (ESS).
Different Access Points within an ESS can use different Channels. In fact, to reduce interfer-
ence, it is recommended that adjacent Access Points SHOULD use different channels.
As Wireless Stations are physically moved through the area covered by an ESS, they will
automatically change to the Access Point which has the least interference or best performance.
This capability is called
Roaming . (Access Points do not have or require Roaming capabilities.)
B