Appendix A; Wireless Lan Overview - Atlantis Land A02-RA241-W54 User Manual

WIRELESS ROUTER ADSL2+

APPENDIX A

Wireless LAN Overview

This section introduces the wireless LAN and some basic configurations. Wireless LANs can
be as simple as two computers with wireless LAN cards communicating in a peer-to-peer
network or as complex as a number of computers with wireless LAN cards communicating
through access points which bridge network traffic to the wired LAN.
Channel
The range of radio frequencies used by IEEE 802.11b wireless devices is called a "channel".
Channels available depend on your geographical area. You may have a choice of channels
(for your region) so you should use a different channel than 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.
ESS ID
An Extended Service Set (ESS) is a group of access points or wireless gateways connected
to a wired LAN on the same subnet. An ESS ID uniquely identifies each set. All access points
or wireless gateways and their associated wireless stations in the same set must have the
same ESSID.
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.
When station A sends data to the ADSL Router, it might not know that the station B is
already using the channel. If these two stations send data at the same time, collisions may
occur when both sets of data arrive at the AP at the same time, resulting in a loss of
messages for both stations.
RTS/CTS is designed to prevent collisions due to hidden nodes. An RTS/CTS defines the
biggest size data frame you can send before an RTS (Request To Send)/CTS (Clear to
Send) handshake is invoked.
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