LWAPP Auto Channel Selection

Unanswered Question
Mar 13th, 2008

I have 5 4404s which have been up in a lab environment for a few months. I just deployed 9 - 1131 APs to my first test site last night. I expected them to automatically set the channel number on the radios however when I checked, 7 of them were at channel 1 and 2 at channel 6. I waited several hours with no change so I then went to each one and manually set the channel I thought it should be set to and then set it back to automatic. After doing some google'ing I found something that said that the DCA runs every 10 min for the first 100 min after a controller reboots but after that will only make channel changes at the pre set anchor-time (12:00pm). Is that right? What is your standard procedure on deploying new APs? Do you “prime” them with the channel you think they should use and then let the WLC adjust them over time once a day? FYI, I have WCS and am running the latest code. Thanks! Doug

I have this problem too.
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Scott Fella Thu, 03/13/2008 - 16:59

it all depends on the installation. Some installs I like to hard set the channel and the power where as others I let RRM do its thing. If you don't feel like the WLC is handling the RRM correctly, then go hard set the AP's. In an area where you have 9 ap's, that shouldn't be so bad to allocate the channels to the AP's. I don't know the answer to how often and when the channel and power setting are checked. If I don't like how the WLC sets the channel after letting it sit for a couple hours to a day, I will hard set the channel or power. Especially when the channels keep changing, then you should intervene and set the channel manually.

everetts33 Sun, 03/30/2008 - 12:48


What criteria do you use to determine if you hard set the channels and power or let RRM do its thing? My company installs into warehouse environments and RRM, prior to 4.1.185, did not appear to be a good thing. After 4.1.185 RRM got better.

Just curious for my own education.



Scott Fella Sun, 03/30/2008 - 13:27


In my opinion I choose to hard set the channels if:

1. RRM changes the channels enough to distrupt service.

2. I don't like the RRM final setting.

In an environment were you are deploying handheld scanners and forklift scanners, any time you have channels adjusting and that propagating to neighbor ap's, users will reassociate and will have to log back on. when there is a persistent connection that needs to happen (telnet / citrix), you need to make sure the RF is stable. if they happen to be running a persistent client, then RRM would be fine.

Now with RRM adjusting power, you must verify you have coverage especially on the edge.

Like I said... this is my opinion from troubleshooting different environments.

everetts33 Mon, 03/31/2008 - 06:52


This is pretty much my approach as well. We will try RRM but if we see issues we will turn it off and manually set the system up. We will then monitor to make sure everything stabilizes.

Thanks for the information. Another opinion is always beneficial.


sabhasin Thu, 03/13/2008 - 17:44

So, first, take a look at the RRM whitepaper which details the "startup time", "anchor time",

"interval" and "sensitivity" for DCA which was first introduced in Here's a link for easy reference:


Having said that, to your specific question:

> but after that will only make channel changes at the pre set anchor-time (12:00pm). Is that right?

No...anchor time is only used as a reference point. it actually matters on the interval that you have configured (defaults to 10min). let's say your anchor time is 12pm and the interval is 2 hours. That means, DCA would run at 2pm, 4pm, 6pm and so on. Oh, and let's say that you rebooted the controller and it came back up at 6pm. From that point on, the startup time kicks in to make sure the network converges before going back to the configured interval and sensitivity. From 6 to 7:40 pm, DCA runs every ten minutes (10 iterations) at high sensitivity. Next run, then, would be at 8pm, at medium sensitivity...

On to the second part of why channels might not be changing in your network....The default sensitivity might not apply to all networks. Perhaps you want to change it to "High". Then, you can look at the traps and see which of the three factors (signal, noise, interference) are causing a channels to change (and adjust sensitivity accordingly). Note - load is disabled by default.

All this and more great late night reading is at the whitepaper i referenced above ;)


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