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Wireless Home Networking for Dummies - Danny Briere, Walter R.Bruce, ....pdf
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314 Part V: The Part of Tens

It’s a good idea to work with a friend or family member. Your friend can be in a poor reception “hole” with a notebook computer with the wireless utility showing the signal strength. You can try moving or configuring the AP to see what works. Just be patient — it can take a few seconds for the signal meter to react to changes.

Because not all performance issues can be tracked down . . . or at least not easily . . . in this chapter, we introduce you to the most common ways to improve the performance or your wireless home network. These are tried- and-true tips, having been there ourselves. We’re pretty good at debugging this stuff by now. We just can’t seem to figure out when it’s not plugged in! (Well, Pat can’t . . . read the next section to see what we mean.)

Check the Obvious

Sometimes, what’s causing you trouble is something simple — and which you can fix simply.

For instance, one of us (and we won’t say who . . . Pat) was surprised that his access point (AP) just stopped working one day. The culprit was his beagle, Opie, who had pulled the plug out of the wall. As obvious as this sounds, it took the unnamed person (Pat) an hour to figure it out. Now if someone told you, “Hey, the AP just stopped working,” you’d probably say, “Is it plugged in?” The moral: Think of the obvious and check that first.

Following are a couple more simple problems to think of first. . . .

Problem: The power goes out and then comes back on. Different equipment takes different periods of time to reset and go through to restart, causing loss of connectivity and logical configurations in your network.

Solution: Sometimes you need to just turn everything off and then turn them back on in order — from the wide area network (WAN) connection (your broadband modem, for instance) back to your machine — allowing each device to start up with everything upstream properly in place and turned on.

Problem: Your AP is working fine, with great throughput and a strong signal footprint, until one day when it all just drops off substantially. No hardware problem. No new interferers installed at home. No new obstructions. No changes of software. Nothing. End cause: The next door neighbor got an access point and was using his on the same channel.

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Solution: This is hard to debug in the first place. How the heck do you find out who is charging invisible interference — by going door to door? “Uh, pardon me, I’m going door to door to try to debug interferers on my access point. Are you suddenly emitting any extraneous radio waves? No, I’m not wearing an aluminum foil hat, why?” Often with debugging perfor-

mance issues, you need to try a lot of the one-step solutions, such as changing channels, to see whether that has an effect. If you can find the solution, you will have a lot of insight as to what the problem was. (If changing channels solved the problem, someone nearby was probably using the same channel, and you can then start tracking down whom!)

The wireless utility for the adapter might have a tab listing the APs in range called a Site Survey or Station List. It might show your neighbor’s AP and the channel that it’s on.

And before you chase a performance issue, make sure that there is one. The advertised rates for throughput for the various wireless standards are pretty misleading. What starts out at 54 Mbps for 802.11a is really more like a maximum of 36 Mbps in practice (less as distance grows). For 802.11b, it’s more like 6 Mbps at best, rather than the 11 Mbps that you hear bandied about. You will occasionally see the high levels (like when you’re within a few yards of the access point), but that’s rare. The moral: If you think that you should be getting 54 Mbps but you’re only getting 38 Mbps, consider yourself lucky.

Move the Access Point

Fact: A wireless signal degrades with distance. You might find that the place where you originally placed your AP doesn’t really fit with your subsequent real-world use of your wireless local area network (LAN). A move might be in order.

After your access point is up and working, you’ll probably forget about it — people often do. Access points can often be moved around and even shuffled aside by subsequent gear. Because the access connection is still up (that is to say, working), sometimes people don’t notice that the access point’s performance degrades when you hide it more or move it around.

Make sure that your AP is where you want it to be. Check that other gear isn’t blocking your AP, that your AP isn’t flush against a wall (which can cause interference), that the vertical orientation of the AP isn’t too close to the ground (more interference), and that your AP isn’t in line of sight of radio wave interference (like from microwaves and cordless phones).

316 Part V: The Part of Tens

Even a few inches can make a difference. The best location is in the center of your desired coverage area (remember to think in three dimensions!) and on top of a desk or bookcase.

For more about setting up access points, check out Chapter 6.

Move the Antenna(s)

Remember the days before everyone had cable or satellite TV? There was a reason people would fiddle with the rabbit ears on a TV set — they were

trying to get the antennas into the ideal position to receive signals. Whether the antenna is on the client or on the access point, the same concept applies: Moving the antenna can yield results. Because different antennas have different signal coverage areas, reorienting it in a different declination (or angle relative to the horizon) will change the coverage pattern. And a strong signal translates to better throughput and performance.

Look at it this way: The antenna creates a certain footprint of its signal. If you’re networking a multi-story home and you’re not getting a great signal upstairs, try shifting your antenna to a 45° angle to increase a more vertical signal — that is, send more signal to the upstairs and downstairs, and less horizontally.

Change Channels

Each AP broadcasts its signals over portions of the wireless frequencies called channels. The 802.11b standard (the most common system as we write) defines 11 channels in the United States that overlap considerably, leaving only 3 channels that don’t overlap with each other. The IEEE 802.11a standard specifies 12 (although most of today’s products only support 8) non-overlapping channels. The 802.11g standard calls for the same 11 channels in the United States as 802.11b, again with overlapping channels.

This affects your ability to have multiple access points in the same area, whether your own or your neighbors’. Because channels can overlap, you can have the resulting interference. For 802.11b 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 like 802.11b further in Chapter 6.

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Check for Dual-Band Interference

Despite the industry’s mad rush to wirelessly enable every networkable device that it makes, a whole lot hasn’t been worked through yet, particularly interoperability. We’re not talking about whether one vendor’s 802.11b PC Card will work with another vendor’s 802.11b AP — 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, or having 802.11a modems and 802.11b modems operating in the same area. In some instances, like the former example, Bluetooth and 802.11b operate in the same frequency range, and therefore do have some potential for interference. Because 802.11a and 802.11b operate in separate frequency bands, they’re less likely to be exposed to interference.

There are also issues with how the different standards are implemented in different products. Some APs that support 802.11b and g, for instance, really support one or the other — not both simultaneously. If you have all g in your house, great. If you have all b, great. If you have some g and the AP detects that b is in the house, it will downshift to b rates. You might be all set, but then your neighbor upstairs buys a b modem (because you’ve said, “Sure, no problem, you can share my Internet connection.”). Not only is he freeloading, but he’s probably forcing your whole AP to shift down to the lower speeds.

To be fair, many of these very early implementation issues are rapidly going away while vendors refine their solutions. Check out how any multi-mode AP that you buy handles multiple forms of wireless connecting to the AP and asking for service. Some of the newer APs compartmentalize their signal so that they can handle two at once, which is very nice and almost necessary.

Check for New Obstacles

Wireless technologies are very susceptible to physical obstacles . . . some more than others. In Chapter 4, we show a Relative Attenuation of RF Obstacles table that tells you the relative attenuation of your wireless signals (radio frequency; RF) as they move through your house. One person in our neighborhood noticed a gradual degradation of his wireless signal outside his house, where he regularly sits and surfs the Net (by his pool). The culprit turned out to be a growing pile of newspapers for recycling. Wireless signals don’t like such masses of paper.