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Mac 911: A wild Wi-Fi ride to hunt a pesky set of problems

Glenn Fleishman | April 6, 2015
There's no technology simultaneously more useful and frustrating than Wi-Fi. Wireless local area networking shouldn't be rocket science at this point, even though it involves fiendish calculations and increasingly sophisticated physics.

I discovered that my main base station was using mixed WPA/WPA2 Personal security, a legacy mode that supports really old Macs and other devices, while the other two base stations used WPA2 Personal. I updated the configuration on the main base station, and the roaming problems have appeared to disappear.

Unfortunately, none of these suggestions helped Aaron.

The signal is coming from inside the house

Aaron turned to local home-theater specialists for help. This profession has grown in leaps and bounds over the last several years as many people have bought an interconnected array of equipment and installed 5.1 or 7.1 speaker systems. Such installers now have to be network gurus, too, because so many devices are Internet or network capable.

Using a site-survey tool, his consultants found 19 networks visible from Aaron's house. The 2.4 GHz band used for Wi-Fi has 14 numbered channels, 11 of which are legal to use in America. (Various channels are available in different countries.) However, adjacent channels all overlap a bit, and can cause network slowdowns. Channels 1, 6, and 11 mostly do not overlap, and Aaron's installer found that all networks he discovered in a scan were on those three channels and most on channel 11. This amount of co-channel usage can definitely crimp reliable throughput.

The installer moved Aaron's 2.4 GHz networks from channel 11 to 8, and fixed a configuration problem that properly split the 2.4 and 5 GHz networks into two unique names. That seems to have done the trick: no more audio stuttering. I typically don't recommend using any but channels 1, 6, or 11, because any other channel interferes with and is interfered from the overlap of at least two other channels' traffic (1 and 6 or 6 and 11).

There's one more trick Aaron didn't employ, but it's useful to know. It's a little-known fact outside of Wi-Fi nerd circles that some 5 GHz channels use much higher-signal strength to send data than others. The low-numbered channels available in many countries (36, 40, 44, and 48) can use just 5 percent — yes, 1/20th! — of the power of a high-numbered channel (149, 153, 157, and 161) under American regulations.

With the default automatic channel setting, a base station will almost always pick a low-numbered channel whenever it's restarted. If you lock the channel to 149 or above, you can often enormously extend the network's range — though you may then interfere with neighbors' networks, which can reduce both networks' maximum throughput.

To change the channel with an Apple base station for either 2.4 GHz or 5 GHz, follow the steps as above to set a 5 GHz network name, and you'll see pop-up options for 2.4 GHz Channel and 5 GHz Channel. If these are set to Automatic, pick channels based on a survey you've done with iStumbler or Wireless Diagnostics, and then click Save and Update to restart the base station with the new settings.


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