Transmit power recommendations for 2.4GHz band

[Bryan J]

We're trying to make our 2.4GHz network more stable and client friendly. One of the issues I want to look into is transmit power settings for that radio band. Any suggestions on how to go about setting a decent Tx power level for the 802.11b/g radios? What have some of you done to help improve the quality of that band?

Controllers: WISM-2 modules running 8.0.140

AP Model: AIR-CAP3702I-A-K9

RRM is set to TPCv2 (Interference)

Power Threshold = -67-dBm

Max Power level assignment = 30-dBm (I know, WAY too high. This has just been left at the default)

Min Power level assignment = 14-dBm

We're a school district, and what was decided when we began the project of getting wireless into our schools was that we would be installing an access point into every classroom in our buildings. Classrooms are an average of maybe 1100-1200-sqft (so around 30-ft x 40-ft). What we typically are seeing is VERY high channel utilization on the b/g radios for access points in any given room, usually higher than 70%. Rx neighbors also tend to show up as high as -35dBm from neighboring rooms. We get complaints from users and on-site tech support of client difficulties connecting to the network or dropping connections, even limited numbers of clients being able to connect to the network (ex: we will get reports of, say, 17 clients connecting and then further devices will have difficulty connecting).

We previously had issues where RRM would configure the Tx power on the b/g radios to most of the time be either 1 or 8, not really balancing anywhere in between to limit coverage to the room to keep bleed-over into adjacent rooms at a minimum. We had adjusted the minimum possible power level in RRM to 14-dBm in an attempt to work on this, but it seems this may have been both too high and in the wrong direction.

Thanks a lot, and any insight is very much appreciated!

[Scott Fella]

I would t use TPCv2!  If you have AP's in every classroom then you can lower the TX or set the max TX to 5 or even 2 and set the min to 2. The 5ghz you want higher so set the max to 11 or 8 and the min to 5. Also you can disable lower data rates. You can make the min mandatory to 36mbps or higher also. I usually set two mandatory rates one is the lowest and 54mbps also for the highest for multicast.  

-Scott 

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[Scott Fella]

I would also make sure band select is enabled and set the cycle count to 5 and then look to see if more devices are moving to the 5ghz and then slowly increase that if you want.  I have gone up to 7 with no issues.

-Scott 

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[Bryan J]

We had tried enabling Band Selection on our main SSID before, but we ran into some major problems with it. The suppression of the 2.4-GHz band traffic ended up causing connection issues for devices, thus inadvertently discovering a major problem we have with a wide array of devices, wireless NICs, and driver revisions out within our schools seemingly acting like 2.4-ONLY devices. It's...a bit finicky, to say the least.

Aside from that, I'm still a little foggy on the use of TPCv1 over v2. I looked back at other posts and found other responses you had given suggesting the same thing on older code revs. It looks like that setting is for much more advanced use, typically only at the instruction of Cisco TAC? Why is that?

[patoberli]

I also suggest to drastically lower the Min Power level assignment! This could be one of the main reasons why it's slow (way to much power on the 2.4 GHz).

I'm having a similar setup in my school (every room one dual-band AP) and have set my RRM settings as follows, which works quite well (sorry for formatting):

DCA:

Avoid Foreign AP interference	Disabled - this is not enabled because we don't have other wireless on our buildings
Avoid Cisco AP load	Enabled
Avoid non-802.11b noise	Enabled
Avoid Persistent Non-WiFi Interference	Enabled

EDRRM Enabled

Sensitivity Threshold

LOW

Rogue Contribution	Disabled

TPC:

TPC Version

Coverage Optimal Mode (TPCv1) ---- TPCv1 chosen

Tx Power Level Assignment Algorithm
Power Level Assignment Method	Automatic
Maximum Power Level Assignment 30
Minimum Power Level Assignment -10
Power Assignment Leader
Last Power Level Assignment

Power Threshold (-80 to -50 dBm)    -67
Power Neighbor Count       3

You might want to increase the Minimum somewhat, but a lot of our walls are thin and don't dampen the 2.4 signal significantly.

[Matthias]

I can confirm that, we have similar TCA settings in a big health care enviroment.

patoberli, how often do you run the DCA? Or is ist freezed?

Thanks

[patoberli]

DCA in 2.4 is running once every 10 minutes and in 5 GHz once every hour. The reason is that we do have one or two places where the users are allowed to use their own Accesspoints for learning and we have quite a few Radar events on the 5 GHz. So freezed is not a good solution in our case.

Also I don't do a new site survey when I replace our APs with a new model.

[Scott Fella]

This was used when AirOS and Converged Access was brought together which you are not using. As far as bacon select, this shouldn't be an issue at all. I have had schools that only also had 2.4ghz devices only and setting band select and ore the cycle count higher did not affect these devices. I have offices now all over the world with a mix of 2.4ghz only with no issue.  If you want 2.4ghz health in your environment, you really need to lower the power down so that you don't have much channel overlap.  You can only get it down to a certain level but it will not be as good as 5ghz due to your high density deployment.  If you can get devices that are dual band off the 2.4ghz, you can possibly lower the channel utilization.  Band Select can identify devices hat are 2.4ghz and will. It suppress their beacons.  That is how band select works.

-Scott 

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[Rasika Nayanajith · Accepted solution]

RRM is set to TPCv2 (Interference)

TPCv1 is the recommended option. Stay with v1

Max Power level assignment = 30-dBm (I know, WAY too high. This has just been left at the default)

In my setup I have kept 11dBm is max

Min Power level assignment = 14-dBm

I have kept 3dBm is min in my setup

Depend on AP density & client capability you have to setup this min/max value. Since most end devices power capability 8-12dBm, it is best if your AP operate in these power levels.

HTH

Rasika

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