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Friday, July 20, 2007

Troubleshooting Wireless LAN Performance at Home

Although troubleshooting any piece of network equipment can be frustrating, when you deal with wireless equipment, it's a little more so because there's so much that you just can't check. After all, radio waves are invisible. That's the rub with improving the throughput (performance) of your wireless home network. And don't get hung up on the term throughput — it's just the actual rate of the data flowing when you take into account retransmissions attributable to errors.

Check the obvious

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

For instance, if someone told you, "Hey, the AP just stopped working," you should 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.

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 performance 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).

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.

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-degree angle to increase a more vertical signal — that is, send more signal to the upstairs and downstairs, and less horizontally.

Check for new obstacles

Wireless technologies are very susceptible to physical obstacles . . . some more than others. One person in our neighborhood noticed a gradual degradation of his wireless signal outside his house, where he regularly sits and surfs the Internet . The culprit turned out to be a growing pile of newspapers for recycling. Wireless signals don't like such masses of paper.

Move around your house and think about it from the eyes of Superman, using his X-ray vision to see your access point. If you have a bad signal, think about what's in the way. If the obstacles are permanent, think about using a HomePlug wireless access point to go around the obstacle by putting an access point on either side of the obstacle.

Install another antenna

A detachable antenna is a great idea because you might want to add an antenna to achieve a different level of coverage in your home. Different antennas yield different signal footprints. If your AP is located at one end of the house, it's a waste to put an omnidirectional antenna on that AP because more than half of the signal might prove to be unusable. A directional antenna would better serve your home.

Antennas are inexpensive and can more easily help you accommodate signal optimization because you can leave the AP in the same place and just move the antenna around until the signal is the best. Within a home, there's not a huge distance limitation on how far the antenna can be away from the AP.

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