802.11n using disabled data rates on 2.4ghz

[sammarshall3]

Firstly here is some background of our deployment.

We have installed several Cisco 2800 APs in an RTLS deployment on 5520 APs code 8.3.143. As expected we are having poor performance on 2.4ghz radios due to too many APs in a given area. We are in the process of fine tuning and we are using FRA (APs in manual mode) to determine which 2.4ghz radios to disable/set to use 5ghz instead. We have found that clients are having "sticky" connections giving poor RSSI and data rates therefore we are about to deploy RF profiles to AP groups with power settings etc. We have already disabled lower data rate on 802.11a and 802.11b/g. For 802.11b/g we have set 11mbps to mandatory and 12mbps+ to supported.

Clients connected to 802.11n on 2.4ghz radios are mostly getting a data rate of 7mbps although they have good RSSI (-50dBm). I am not sure what is causing this the SnR seems ok to me. I didn't think that clients would be able to get data rates that low if they are disabled globally for the radios but must be misunderstanding something. Is anyone able to help to explain this and also offer any good tuning advice.

Many thanks

[Leo Laohoo]

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@sammarshall3 wrote:

We have installed several Cisco 2800 APs in an RTLS deployment on 5520 APs code 8.3.143. As expected we are having poor performance on 2.4ghz radios due to too many APs in a given area. We are in the process of fine tuning and we are using FRA (APs in manual mode) to determine which 2.4ghz radios to disable/set to use 5ghz instead. We have found that clients are having "sticky" connections giving poor RSSI and data rates therefore we are about to deploy RF profiles to AP groups with power settings etc. We have already disabled lower data rate on 802.11a and 802.11b/g. For 802.11b/g we have set 11mbps to mandatory and 12mbps+ to supported.

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Everything written in this paragraph is the complete opposite of "RTLS".  Let me explain: 

1.  RTLS requires 2.4 Ghz because old 2.4 Ghz radio is a lot cheaper than old/newer 5.0 Ghz radio.  Take note, I said "OLD". 

2.  Old 2.4 Ghz radio also means the tag doesn't like talking high data rates.   Some RTLS tags might say in the brochures that they support 802.11g data rates what the brochures and technical support won't tell anyone is the tags will need 1 Mbps data rate to make the initial "connection".  

3.  Because they are all 2.4 Ghz, enabling FRA is counter-productive as FRA will immediately turn off 2.4 Ghz radio of the AP and switch to micro-5.0 Ghz.  

4.  RTLS like static power & static channel assignment.  So turn off DCA, RRM and CleanAir (better to deploy autonomous AP). 

Hope this helps.

[sammarshall3]

Thank you. I really don't want to do everything statically. I have no problems using RF profiles to help with power settings etc I just feel that making everything static will mean that if we get any wireless interference from neighbouring companies wireless systems we will experience poor performance until we manually change everything

We planned to use FRA in manual mode to make suggestions as to which APs to change and to which modes then we could make a decision as to what ones we wanted to do.

We still want to have 2.4 coverage we just can't have it enabled on every AP as it's causing performance issues. Are you suggesting to keep all 2.4 radios enabled and just reduce the power settings of each AP?

If you have any good resources for RTLS best practices or tuning please can you share as it would be most helpful.

Many thanks

[Leo Laohoo]

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@sammarshall3 wrote:
Are you suggesting to keep all 2.4 radios enabled and just reduce the power settings of each AP?

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Ok, let me give you a recent example:  

We upgraded a building (about 100 APs) to 2800.  The controller is running 8.8.125.0 and we had FRA turned on (no brainer).  The problem we've got is the APs are in a "high density" deployment due to RTLS.  So when FRA kicked in, there was less than 15 APs with 2.4 Ghz.  

We had to manually disable FRA on a per-AP basis just to get RTLS to an "acceptable" level.  This means throwing away "self-healing" wireless network.  

Another thing, we had to enable an RF Profile that enables 1 Mbps data rate.  

When we asked the vendor if they can release a patch to get the tags to operate "better" they laughed because money's-been-paid and the cheque-has-cleared.  

[Haydn Andrews]

If the RTLS tracking is required for 2.4GHz clients, FRA will cause issues. You are better manually disabling 2.4GHz radios (or better yet putting it to monitor mode) as i had FRA turn off all the perimeter APs and accuracy went out the window.

If you have an RTLS design there is a high likely hood that a site survey was conducted, you could use this to simulate which APs you could turn off the client servicing 2.4 GHz radio on.

When you turn off FRA globally, you will potentially have to reset the APs XOR radio back to 2.4 or monitor mode. There use to be a bug where it didn't like it.

I have also had a version of WLC code where clients get stuck to the micro cell and don't roam well which is another reason i turned off FRA.

When your seeing 7mbps is this from the client or the WLC? 

[sammarshall3]

Thank you. Yes we had a site survey completed using Ekahau. We were advised that due to the number of APs in close proximity to each other we would need to disable some of the 2.4 radios. We only planned to use FRA in manual mode so that we use its suggestions for which ones to change to 5 or put in monitor mode.

We had left Clean air DCA and RRRM enabled in the hope that power and channel settings would automatically be set to how was needed but we are getting such poor performance on 2.4. I cannot understand why clients are getting 7mbps data rates when they have such strong signal and the AP is not overloaded. We are seeing the client data rate on the WLC but also users are reporting such poor performance and we can see that their data rates on their clients are very poor.

Please may I ask what other tuning or configuration you applied to optimise RTLS in your environment? 

Thanks

Sam