Cisco – wifi access points in a noisy environment

aironetciscoieee 802.11wireless

I have a bunch of Cisco AIR AP 1602e, which I have configured. These are dual-band a/b/g/n access points. Sometimes my users do expirience lags and spikes, even the associations start to break (for some of the users). This WLAN is deployed in a large office buildings, occupied by a number of organizations, and a scan from a FreeBSD machine reveals more than 18 (!) SSIDs on 2.4 GHz, without taking into account my own SSIDs. In the same time carrier busy test for 2.4 Ghz show busy rates for a set of channels where 17% is the minimum, and the maximum sometimes can go up to 71% (!). The 5 GHz range isn't that overcrowded (5-15% at the CBT), but still, spikes happen: sometimes once a week, sometimes less frequently.

What is the best strategy to mitigate this ? You should take into the considerations the following measures I attempted:

  • all of the APs are standalone ones, WDS is configured and running.
  • all of the APs are equipped wuth 2/4 dBm omnidirectional dipole antennas.
  • Cisco 1602e APs are capable of the CleanAir functionality, but only with wireless controller, which I don't have.
  • all of the APs are running the latest Cisco IOS. This doesn't seem to affect the spikes in any way
  • I disabled the 802.11b rates entirely, leaving only a, g and n rates. I don't have the statistics for this as of yet (does it affect sipes or not).
  • seems like some of the low-end crappy adapters, like D-Link or even (shame ! but some of the users happen to use this so-called equipment) TP-Link do not handle well AES/CCKM cipher rotation scheme, so I have to create them a separate legacy WPA/TKIP SSID, at least the last couple of days I didn't hear any complaints.
  • I did tamper with transmit power, I have set the transmit power at its maximum, and at it's minimum, – this didn't affect spikes in any noticeable way. At this times all of the APs are running at their minimum transmit power.
  • I disabled the 2.4 GHz band for all of the SSIDs that dual-band modern clients are sitting in, but for this moment I didn't have the statistics yet. I am aware about the band-select feature, but event when it's enabled lot of clients prefer the 2.4 Ghz band (for some reason that is unknown to me).

Best Answer

It sounds like you've done all the right things:

  • Move to 5 GHz where clients allow
  • Disable slow speeds
  • Limit xmit power

The basic problem is you're working in a crowded RF environment and there's not a lot you can do. It's rush hour on the freeway, and no matter how powerful a car you have, you can only go as fast as the flow of traffic.

Until you can upgrade the rest of your clients to use 5 GHz, you may be doing as well as you can.

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