Wi-Fi Shopping 101

If you’re like me, when you go shopping for a Wi-Fi device, either online or
at your local electronics superstore, you can find it much too easy to be confused
by the wide variety of available access point-type equipment.

It’s bad enough that we have to cope with three main kinds of Wi-Fi standards–the
2.4GHz 802.11b and 802.11g as well as 5GHz 802.11a –but that’s just the beginning.
You next have to figure out exactly what device you need. And, that’s not always
an easy job.

The best way to do this is to know exactly what job you want your new Wi-Fi
device to fill in your home or office.

Basic Home Internet Sharing

Many people just want to share a home broadband connection with everyone in
the household. The best device for that is a wireless router (that is, a cable
modem/DSL router with an access point built in). Typically, you’ll attach this
device between your broadband modem and your main PC. Examples of these routers
include the Buffalo
AirStation 54Mbps Broadband Router AP
, the Netgear
Cable/DSL Wireless Router 54 Mbps/2.4 GHz
and the Belkin
802.11g Wireless DSL/Cable Gateway Router
. All of the above support 802.11g.

These routers usually come with four wired Ethernet ports and an additional
Ethernet port for your cable or DSL modem. For normal home installation though,
you’ll only need the broadband socket and one of the other ports for your main
PC.

You can expect to pay about $120 for a basic Wi-Fi router. If you want more,
say support for both 802.11a and 802.11g, the price will jump up to about $200.
You can expect prices to drop, though, for these, and indeed all Wi-Fi equipment
in the coming months as Intel Centrino and other chips, plus more chipmakers
from around the world, price pressure on all Wi-Fi equipment makers.

SOHO LANs and Internet Sharing

If you have a small office/home office (SOHO), a broadband Wi-Fi router may
still be all you need. But, if your office is spread too far for a single router
to do the job, you’ll want to look into true access points and access point/print
server combinations.

An access point does just what it name says: it’s an access point for Wi-Fi
equipped PCs and access pointtops. Unlike a wireless router, though, it doesn’t
serve as a gateway to the Internet. That doesn’t mean you couldn’t use an access
point as your sole Wi-Fi device. But to go online does you’d need to use either
a separate router, or run a program such as Windows’ built-in Internet Connection
Sharing (ICS) to serve as a router so that every computer on your network can
reach the Internet. This, as you would guess, is more complicated and isn’t
recommended for network novices.

If you deploy an access point with already existing Wi-Fi devices, you must
also be sure to set the Wi-Fi channels so that they don’t overlap. Usually,
this means that they need to be at least four channels apart. For example, with
802.11b and 11g you should use channels 1, 6 and 11. Otherwise you’ll find your
network having more than its share of odd connection problems. For more on avoiding
coverage problems see: Are Site Surveys
Necessary?

If you have a remote printer, you can also use a combination access point/print
server to spread coverage and let users access one or more printers at the same
time. Typically, in a large network environment, you’d have dedicated print
servers for this job, but if some of your printers and main office are removed
from each other access point/printer servers make sense for small offices.

Middle Sized Offices and Beyond

What if your office extends to two or more floors of a building? The best way
to handle this is probably to lay cable between a switch or a router to two
or more access points. But, you can find devices called bridges to connect between
floors.

Wi-Fi bridges, like the Linksys WET11 Wireless
Ethernet Bridge
, do exactly what the name say says. They allow wireless
traffic to bridge across a distance. Some access points can go into bridge mode
(like Buffalo’s router) but not all bridges provide access point services.

Cheap Wi-Fi bridges do point-to-point connections — think of it as a wireless
cable. So, for example, the WET11 would let you connect the third floor offices
with the forth floor’s server room. But, if you want to connect more than one
access point to a single bridge, you need one that can handle point-to-multipoint
connections like the D-Link AirPremier DWL-1750
Outdoor 2.4GHz Wireless Bridge Router
.

If you want one box to both span distances and work as an access point what
you usually want is a repeater. These can also go by such names as signal amplifiers,
boosters or kickers.

Repeaters like the D-Link AirPlus
DWL-800AP+ Enhanced 2.4GHz Wireless Range Extender
repeats a signal it
receives from either an access point or from an Ethernet cable. What you end
up with is much broader coverage from what access pointpears to be a single
access point.

Repeaters tend to be extremely touchy with what equipment they’ll work with
–D-Link’s only works with other D-Link products — so I strongly recommend
that you only use them with the recommended equipment from the same vendor.

Of course, simply using the right antenna can also help these problems. For
more on that see Antennas: The
Key to Maximizing RF Coverage
.

Beyond 802.11

With the right antennas, you can even span miles with 802.11b. But, for most
of us, once you move to hundreds of yards instead of feet, you’ll want to look
to other technologies instead of 802.11 for your connectivity.

Still, with the right mix of devices, there’s no reason you can’t cover a small
campus or a good-sized building with Wi-Fi coverage. It may not always be the
best solution, and there’s a lot to be said for Fast Ethernet 100Mbps speeds,
but if you’re in a situation where Wi-Fi’s comparatively low speeds are sufficient
or pulling cable is prohibitively expensive, than Wi-Fi is an inexpensive and
efficient way to go.

Too Many DHCP Servers

Far too many Wi-Fi access point devices come with Dynamic Host Configuration
Protocol (DHCP) servers installed and running by default. For home or SOHO
users, that’s a blessing. For everyone else, it’s a curse.

On medium sized or larger networks, you almost certainly already have a DHCP
server providing IP addresses. While in theory some such servers, such as Windows
2000 Server and Windows Server 2003, can automatically shut down or close off
other non-authorized DHCP servers, in practice they usually don’t.

So, what happens then is your DHCP enabled Wi-Fi access point in the office
on the outside building can start fouling up valid IP address assignments. The
puzzled PCs default to a private IP address in the 169.x.x.x range without any
valid gateway or DNS addresses. For most practical purposes, this knocks these
PCs off the network. This is not good.

Prevention is the best cure. Anytime you install a Wi-Fi ACCESS POINT of any
sort on a network that already has DHCP working, check, and then double check,
that its internal DHCP is turned off. If you don’t, I can almost guarantee you
that you’ll face unexplained PC network failures across both the Wi-Fi and wired
network.

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