ZyXEL Communications Internet Security Gateway ZyWALL 2 Series User Manual page 548

ZyWALL 2 Series User's Guide
Spread Spectrum (DSSS) and Frequency-Hopping Spread Spectrum (FHSS), in the 2.4 to 2.4825 GHz
unlicensed ISM (Industrial, Scientific and Medical) band. The third method is infrared technology, using
very high frequencies, just below visible light in the electromagnetic spectrum to carry data.
Ad-hoc Wireless LAN Configuration
The simplest WLAN configuration is an independent (Ad-hoc) WLAN that connects a set of computers with
wireless nodes or stations (STA), which is called a Basic Service Set (BSS). In the most basic form, a
wireless LAN connects a set of computers with wireless adapters. Any time two or more wireless adapters
are within range of each other, they can set up an independent network, which is commonly referred to as an
Ad-hoc network or Independent Basic Service Set (IBSS). The following diagram shows an example of
desktop and notebook computers using wireless adapters to form an Ad-hoc wireless LAN.
Diagram D-1 Peer-to-Peer Communication in an Ad-hoc Network
Infrastructure Wireless LAN Configuration
For Infrastructure WLANs, multiple Access Points (APs) 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. All communications between stations
or between a station and a wired network client go through the Access Point.
The Extended Service Set (ESS) shown in the next figure consists of a series of overlapping BSSs (each
containing an Access Point) connected together by means of a Distribution System (DS). Although the DS
D-2 Wireless LAN and IEEE 802.11