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MVP
Posts: 1,111
Registered: ‎10-11-2011

Getting Better Channel Re-use

Occasionally, we'll have issues with neighboring APs selecting the same channel on 5GHz.  We recently started adding DFS channels to our regulatory domain and have thus far added 4 extra DFS channels.  Just from that perspective, there are plenty of channels to go-around.

 

Most of the channel changes should occur at night when most APs don't have any clients associated. So it may be that AP1, without any clients, changes channels due to interference or free channel, which happens to be the same channel as its neighbor, AP2.  Since 'client-aware' is enabled, AP2 may be stuck there until its clients roam/disconnect.  I thought about running a script nightly that would disable client-aware, so APs can shift channels at night, but this just opens us up to more channel changes, resulting in a very dynamic environment.  I'd prefer to be a bit more stable.

 

Any suggestions for getting better channel re-use, just short of creating a static channel plan?

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Guru Elite
Posts: 21,567
Registered: ‎03-29-2007

Re: Getting Better Channel Re-use

Thecompnerd,

The "best" channel plan is dependent on many variations that could happen throughout the day. If you have a static plan, there is nothing to say that channel X will become either congested, impaired or unusable throughout that day. ARM changes channels in response to changing conditions that are unavoidable, but that can be worked around. You should take a look at the RF conditions historically to understand if that channel was usable or even impaired at the time to understand what is happening. In a perfect world, the channels would be distributed evenly and never change. This was achievable in environments with little to no density. It is almost nonexistent in environments with high density because the conditions can change so suddenly.


Colin Joseph
Aruba Customer Engineering

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MVP
Posts: 1,111
Registered: ‎10-11-2011

Re: Getting Better Channel Re-use

In our environment, I wouldn't expect strong 'outside' RF interferers since the building is not in close proximity to other businesses.  I do see mesh networks and other outside 802.11 RF bleed in, but it's usually not too strong.  We don't have a problem with mi-fi's or other portable wi-fi sharing devices, since this is a business.  For these reasons, I've often thought that the dynamic nature of ARM does not benefit us, since we need the environment to be stable with good channel separation, more than anything.

 

Static channel plan is still my last resort, but out of curiosity, what happens if an AP is assigned a DFS channel and radar is detected?  Will the AP vacate the channel and come back to it in 30 min?  If a dynamic channel plan was instead used, I believe the AP would just move to another channel.  So that is one concern I'd have using a static channel plan with DFS channels.

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Guru Elite
Posts: 21,567
Registered: ‎03-29-2007

Re: Getting Better Channel Re-use

You are more likely to get RF issues from high utilization created by your own clients than outside interferers in a high density situation.  You can have static channels, but they can do nothing to deal with random, sustained high utilization from groups of clients.  ARM looks at interference as well as channel quality (high utilization) when considering a new channel for an access point.  Channel separation is meaningless if an entire channel that clients are on becomes unusable for whatever reason and your clients stay on that access point.  This is in addition to the probable co-channel interface that is already part of a high-density WLAN.

 

If an access point detects radar  on a channel, the AP changes channel immediately and cannot return to that channel for 30 minutes.  The AP is free to choose any other channel, but there is no need or requirement to return to that same channel.

 

 



Colin Joseph
Aruba Customer Engineering

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