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Archive for November 2012

Back To Basics (Again)

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The hot topic in WiFi nowadays is high density (HD), and for good reason.  It seems you can’t swing a dead cat anymore without hitting some place (concert hall, convention center, tourist trap) where there’s an attempt to offload cell phone data onto a WiFi network.  The most interesting thing about HD WiFi to yours truly is that it’s the same fundamentals we’ve always known about, just recycled.

If you were one of the lucky (unlucky?) ones to work in WiFi during its more formative years, you may have been taught certain basic concepts about WiFi.  For the author, fond memories still remain of sitting an Enterprise WLAN Administration course way back in 2003 (taught by noted Massachusetts Yankees fan David Westcott) as part of my preparation for the certified wireless network administrator (CWNA) exam.

What did Mr. Westcott teach us lo these many years ago?

Plan out your space alternating between channels 1, 6 and 11 in the 2.4 GHz band.

If APs are spaced too close together, adjacent channel pairs (1 & 6 or 6 & 11) will interfere.

Keep the transmit power of your APs near 30 mW (which was the typical transmit power of an 802.11b PC card).

Use directional antennas whenever you can.

Use 802.11a in high usage areas because the 5 GHz band has more channels.

Do any of these things sound familiar?  Does this nine-year old information resonate today?

If you have designed, deployed, managed or troubleshot a HD WiFi installation, these rules should sound familiar.  Some of the details may have changed (stations that dynamically adjust transmit power; more 5 GHz channels; 40 MHz channel options in 802.11n), but the basics are the same as they always were.

During the Dark Ages of WiFi (I just watched The Name Of The Rose, so I’ll choose that term instead of “Medieval WiFi”), just about everyone everywhere was trying to beat the basics.

Remember adaptive transmit power on APs?

Remember automatic channel selection?

Remember trying to use channels besides 1, 6 and 11?

Remember co-locating 2.4 GHz AP radios close to each other, or even in the same box?

Remember APs without external antenna interfaces?

Actually, all of these things still exist.  And they all are still used, and — in some unfortunate cases — these things are used for HD WiFi.  None of them should be* (save auto channel selection, which still works in the 5 GHz band), but when WiFi folks fail to learn WiFi basics, these things happen.

There was one other thing that Mr. Westcott taught us during that August in Pasadena so long ago.  He taught us the importance of analysis.  He taught us that if you can’t see what’s going through the air, you’ll have a tough time getting your infrastructure optimized.  That basic of WiFi still applies, too.  Learn your sniffers, folks.  Get familiar with WildPackets OmniPeek or Fluke AirMagnet WiFi Analyzer (or if you prefer to save a little bit of money and waste a whole lot of time, Wireshark) and get yourself a good portable spectrum analyzer (I like Metageek Chanalyzer with WiSpy DBx) to go with it.

*If you’re supporting low density, non-mobile WiFi, then by all means use those outdated WiFi design principles and features.  Just keep that crap away from sports facilities.  Yes, I am there to watch the Milwaukee Bucks, but I also would like to set my DVR from my seat if I forgot to record The Mindy Project.

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Written by sniffwifi

November 30, 2012 at 9:16 pm

Posted in Uncategorized