Struggling with the 2.4GHz band and older clients

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Hey all,

We're having some random issues especially with older / "cheaper" laptops (Windows only - no issues with oldschool Macs) in our network. They are all on the 2.4 GHz frequency band. Signal strength is usually pretty high (at least the icon indicates that). People never actually lose the connection. However, they experience super slow speeds, like 0.5 down and 0.1 up. The only fix is disabling the wifi card (and re-enabling it), or they can simply wait - after about 5 or 10 minutes or so, everything is back to normal.

Please see the file attached (arrows indicate these "dead zones"). Any recommendations what I should change / "tweak"? Our location here is pretty challenging: we have super high ceilings (no ceiling tiles, everything is exposed, including some really really big HVAC ducts).

Thanks and all the best,
Roman

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Roman Kern

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Posted 4 years ago

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Crowdie, Champ

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Have you completed 2.4 GHz co-channel contention testing?  Basically are your 2.4 GHz radios shouting over the top of each other.

The other common cause of this is incorrect transmit power settings.  If your 2.4 GHz radios are transmitting higher than 15 dBm then I can almost guarantee that you will have some 2.4 GHz clients that are reluctant to roam (i.e. they have become "sticky") and, hence, are not roaming to the optimal 2.4 GHz radio resulting in poor performance.  This seems likely as you say that if you turn their wireless NICs off and on they get a performance improvement - this could be because you are forcing the wireless NIC to associate to the nearest 2.4 GHz radio rather than holding association to a 2.4 GHz radio fifty meters away.

To work out the optimum maximum transmit power is difficult without some onsite analysis but generally 15 dBm is a good starting point as smartphones and tablets seem to perform well around this transmit power level.
(Edited)
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Roman Kern

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Thanks Crowdie!
Have you completed 2.4 GHz co-channel contention testing?
Absolutely not... I honestly also don't know how to do that, I mean, like on a "semi-professional" level. Can you point me into the right direction?

I totally agree, I think
  1. that we might have the 2.4 band turned on in the wrong access points (see the map in my original post) - I am also not sure though how I should decide which AP should have it turned on at all
  2. I already reduced the transmit power on all APs (however, also not really sure how far I should go down here - will change it to 15dBm now, thanks for the suggestion!), and I think that most of the clients which report issues are either located in a "dead zone" or in a "sticky area".
It is super challenging to "fine tune" the setup...
Thanks again
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Crowdie, Champ

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You need to be able to determine which 2.4 GHz radios are transmitting where.   The best way to do that is with a site survey application such as AirMagnet's Survey PRO (http://www.flukenetworks.com/products/airmagnet-survey) or Ekahau's Site Survey Professional (http://www.ekahau.com/wifidesign/ekahau-site-survey).  Once you are finished "mapping" the area you can easily see where the access points are and how far their signal is propagating.  With this information you can decide if you need to lower the 2.4 GHz maximum transmit power and/or disable some of the 2.4 GHz radios.

If you are on a Scottish budget (i.e. zero) have a look at Ekahau's HeatMapper free application (http://www.ekahau.com/wifidesign/ekahau-heatmapper).  It may do what you need.

The "Maps" area of HiveManager is nice to show end users some pretty colours but, IMHO, is not worth too much more.  You certainly can't design a wireless network with it and it was never designed to be used as such.

It is super challenging to "fine tune" the setup...
This is what a wireless engineer commonly does.  Being able to throw a few access points up around a site is really easy.  Fault finding those access points is a different story.
(Edited)
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Roman Kern

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Got it, thanks! I will start with the Heat Mapper app first and then do the Ekahau survey afterwards. Will update this thread afterwards. Best
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J. Goodnough, Champ

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This is a good place to point out that setting the power level on the 2.4 radio to 15 in the AH gui DOES NOT MEAN that the broadcast power is set to 15 dBm.
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Roman Kern

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Ha, so where would I change the actual broadcast power (and what is the "Power" setting in the HiveManager then)? Thanks!
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J. Goodnough, Champ

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Roman Kern

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Thanks!! - I am getting a 404, can you re-post that link?
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J. Goodnough, Champ

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Actually, I can't, sorry - in summary it's a known situation and AH is working internally on the best way to resolve it