Wi-Fi Shopping 101
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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.
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
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.