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2776 Views 4 Replies Latest reply: Aug 20, 2010 2:06 PM by Stephen Ellis RSS

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802.11a Channel DCA Issues?

Aug 19, 2010 1:19 PM

Stephen Ellis 14 posts since
Jul 21, 2008

Hi Guys

 

Wondered if anyone can help?

 

I installed a new 5508 controller and ten APs at a customer site recently. I configured the controller so that Data clients use 802.11g/n and voice clients use 802.11a (7921G phones so no 'n'). The building is a large warehouse with offices stretching along a corridor at the front of the building. The warehouse is split into two, one large empty space (for expansion) and one area that is in use. From the results of an AirMagnet WLAN survey I performed, 6 APs were deployed in the main halls. The issue I have is that all ten APs have defaulted to Channel 36. Is this normal behaviour? DCA/Auto Tx Power are both enabled.

 

Cheers in advance.

 

Stephen

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,398 posts since
    Oct 7, 2008
    Currently Being Moderated
    1. Aug 19, 2010 7:34 PM (in response to Stephen Ellis)
    Re: 802.11a Channel DCA Issues?

    You can independently play with the power levels on the A radios if you need to, but once they "see" each other they should shift channels.

     

    I just did a 5508 install on Monday, and I did notice it took about 6 hours to everything to sort itself out (both 5G and 2.4G were freaking me out being on mostly a single channel each) but then it all got sane.

     

    How long did things rest on your side?  I'll assume all your other settings were at default for RF management?

     

    Scott

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,398 posts since
    Oct 7, 2008
    Currently Being Moderated
    3. Aug 20, 2010 4:55 AM (in response to Stephen Ellis)
    Re: 802.11a Channel DCA Issues?

    My only guess on that is that your site survey may have been done with 2.4GHz in mind.  The falloff for 5GHz is faster, so while your b/g radios may see each other just fine and adjust, the a  radios (for whatever reason in your layout/RF interference) may not.

     

    Also, if 2.4GHz is congested for you, then the radios will try to find the least congested one.  5GHz will too, but if nothing is there AND if they don't really see each other, then they'll stay at the default.

     

    I agree with you, the WLC is smarter than we are. At least when it works right.  Otherwise, it's not entirely helpful!

     

    Do you have a good wireless tester or spectrum analyzer?  Perhaps you can wander around and see where the overlap points are between APs and try to determine whether the A radios could see each other like they're supposed to.  (or just up the power level on A and see if that helps them discover each other!)

     

    Scott

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