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

    802.11a Channel DCA Issues?

    Stephen Ellis

      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

        • 1. Re: 802.11a Channel DCA Issues?
          Scott Morris - CCDE/4xCCIE/2xJNCIE

          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

          • 2. Re: 802.11a Channel DCA Issues?
            Stephen Ellis

            Hi Scott

             

            Thank's for replying. The controller and APs have been installed for about two weeks now. I haven't tweaked with anything really, just left everything automatic to let the controller decide how to run things (it's smarter than me ). There are a lot of interfering devices on the 2.4GHz frequency which the customer assures me he is going to get rid of but I wouldn't have thought this would affect the a radio channel distribution (there's nothing currently transmitting at 5GHz).

             

            Ta

             

            Stephen

            • 3. Re: 802.11a Channel DCA Issues?
              Scott Morris - CCDE/4xCCIE/2xJNCIE

              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

              • 4. Re: 802.11a Channel DCA Issues?
                Stephen Ellis

                Yeah, I think I revisit and post-install survey is overdue on this one.

                 

                Cheers

                 

                Stephen