Wireless Home Networking - Index of

Chapter 18: Ten Ways to Troubleshoot Wireless LAN Performance
products support only 8) nonoverlapping channels. The 802.11n draft 2.0 proposal
uses the same 11 channels as 802.11g at 2.4 GHz and the 12 channels of
802.11a at 5 GHz in the United States, again with overlapping channels.
802.11n is designed to work with all the previous standards. The dynamic
switching of channels on either frequency available to it means you have a lot
less to configure during setup. Some single-frequency APs still give you the
option to choose channels at the beginning, but they don’t necessarily have
to stay on that channel as they work.
This situation affects your ability to have multiple access points in the same
area, whether they’re your own or your neighbors’. Because channels can
overlap, you can have the resulting interference. For 802.11g access points
that are within range of each other, set them to different channels, five apart
from each other (such as 1, 6, and 11), to avoid inter-access point interference.
We discuss the channel assignments for wireless LANs further in
Chapter 6.
Check for Dual-Band Interference
Despite the industry’s mad rush to wirelessly enable every networkable
device it makes, a whole lot hasn’t been worked through yet, particularly
interoperability. We’re not talking about whether one vendor’s 802.11g PC
Card works with another vendor’s 802.11g access point — the Wi-Fi interoperability
tests usually make sure that’s not a problem (unless one of your
products isn’t Wi-Fi certified). Instead, we’re talking about having Bluetooth
(see Chapter 15 for more on this technology) working in the same area as
802.11b, g, and n, or having older 802.11a APs and 802.11b, g, and n APs operating
in the same area. In some instances, like the former example, Bluetooth
and 802.11b, g, and n operate in the same frequency range, and therefore have
some potential for interference. Because 802.11a and 802.11b, g, and n operate
in separate frequency bands, they’re less likely to be exposed to interference.
Some issues also exist with how the different standards are implemented in
different products. Some APs that support 802.11g and n, for example, really
support one or the other — not both simultaneously. If you have all g in your
house, that’s great. If you have all n, that’s great. If you have some n and the
access point detects that g is in the house, it could downshift to g rates.
You may be all set, but then your neighbor upstairs may buy a g network
adapter (because you’ve said “Sure, no problem, you can share my Internet
connection.”). He’s not only freeloading, but he also could be forcing your
whole access point to shift down to the lower speeds.
To be fair, many of these very early implementation issues have gone away
while vendors refined their solutions. Check out how any multimode access
point that you buy handles dealing with more than one variant of 802.11 at
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