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Switzerland
•
Studerus AG
Turkey
•
ZyXEL Turkey A.S.
UK
•
ZyXEL Communications UK Ltd.
Ukraine
•
ZyXEL Ukraine
Latin America
Argentina
•
ZyXEL Communication Corporation
Brazil
•
ZyXEL Communications Brasil Ltda.
Ecuador
•
ZyXEL Communication Corporation
Middle East
Israel
•
ZyXEL Communication Corporation
Middle East
•
ZyXEL Communication Corporation
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North America
USA
•
ZyXEL Communications, Inc. - North America Headquarters
Oceania
Australia
•
ZyXEL Communications Corporation
Africa
South Africa
•
Nology (Pty) Ltd.
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A
PPENDIX
B
Wireless LANs
Wireless LAN Topologies
This section discusses ad-hoc and infrastructure wireless LAN topologies.
Ad-hoc Wireless LAN Configuration
The simplest WLAN configuration is an independent (Ad-hoc) WLAN that connects a set of
computers with wireless adapters (A, B, C). 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 notebook computers using wireless adapters to form an ad-hoc wireless LAN.
Figure 169
Peer-to-Peer Communication in an Ad-hoc Network
BSS
A Basic Service Set (BSS) exists when all communications between wireless clients or between a
wireless client and a wired network client go through one access point (AP).
Intra-BSS traffic is traffic between wireless clients in the BSS. When Intra-BSS is enabled, wireless
client
A
and
B
can access the wired network and communicate with each other. When Intra-BSS is
disabled, wireless client
A
and
B
can still access the wired network but cannot communicate with
each other.
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Figure 170
Basic Service Set
ESS
An Extended Service Set (ESS) consists of a series of overlapping BSSs, each containing an access
point, with each access point connected together by a wired network. This wired connection
between APs is called a Distribution System (DS).
This type of wireless LAN topology is called an Infrastructure WLAN. The Access Points not only
provide communication with the wired network but also mediate wireless network traffic in the
immediate neighborhood.
An ESSID (ESS IDentification) uniquely identifies each ESS. All access points and their associated
wireless clients within the same ESS must have the same ESSID in order to communicate.
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Figure 171
Infrastructure WLAN
Channel
A channel is the radio frequency(ies) used by wireless devices to transmit and receive data.
Channels available depend on your geographical area. You may have a choice of channels (for your
region) so you should use a channel different from an adjacent AP (access point) to reduce
interference. Interference occurs when radio signals from different access points overlap causing
interference and degrading performance.
Adjacent channels partially overlap however. To avoid interference due to overlap, your AP should
be on a channel at least five channels away from a channel that an adjacent AP is using. For
example, if your region has 11 channels and an adjacent AP is using channel 1, then you need to
select a channel between 6 or 11.
RTS/CTS
A hidden node occurs when two stations are within range of the same access point, but are not
within range of each other. The following figure illustrates a hidden node. Both stations (STA) are
within range of the access point (AP) or wireless gateway, but out-of-range of each other, so they
cannot "hear" each other, that is they do not know if the channel is currently being used. Therefore,
they are considered hidden from each other.
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