4. January 2012 by admin.

The relatively new WLAN spec for 802.11n makes many promises… faster speeds, farther reach, stronger connections, more secure… well, maybe.

The new frequencies lie somewhere within the 5 GHz band.  Why do I say “somewhere”?  Because this new “standard” uses a technology called DFS which stands for Dynamic Frequency Selection. In essence the channel can be automatically changed to avoid interference.  Sounds good huh? … well, maybe.

Does 5 GHz sound familiar to some of you?  That may be because it is also where all 12 channels of the three “Unlicensed National Information Infrastructure” (UNII) 5 GHz bands live. That’s also where my cordless phone calls home.  The U.S. military sometimes runs in 5 GHz as does weather radar and others. Starting to sound a little crowded?

So it falls to the equipment vendors to develop their offerings in such a way as to avoid these problems… well, maybe.

The vendor must get its products that use DFS, certified by the FCC for use in 5.25 to 5.35 GHz and 5.47 to 5.725 GHz ( painfully close to my 5.8 GHz phone system). If not, they have to block those channels, which means you won’t have access to the whole available block of frequencies.

You probably won’t want to run important applications on the UNII-2 bands because these are the areas where DFS channel changing may be an ongoing problem for your location. This is going to result in a lot of delays and an unreliable wireless network.  Some systems actually have to reboot after traffic has been switched to a different location in the electromagnetic spectrum.

So yeah… it’s going to be cool…. maybe.  Check things out carefully before you toss a lot of cash into any particular deployment strategy.

Good Luck and Good Networking.

From down in the trenches,  I’m Tom

Posted in DFS, 802.11n, FCC, WLAN, Wireless, Networking, Troubleshooting, Computers | Print | No Comments »