LWAPP Site Survey methodology

[john.preves]

I have been doing site surveys the "old fashioned" way for quite some time.

I am interested in how the survey is performed utilizing the new lightweight AP's.

Mainly, how do you determine AP location if there is no way to configure the AP itself?

Do these surveys require the use of a Controller?

Can I still design the infrastructure to physically load balance the network or am I at the mercy of this little box?

Also, do I have any control over channel allocation? I don't like to put channel 11 near Microwave ovens if I can help it, but I would like to know that if any thing gets switched, is it going to be switched back?

Any links that would describe the "new" survey process would be very apprieciated.

Thanks-

[john.preves]

apparently, you still need an autonomous AP to perform the survey.

According to every thing I have read so far, nothing specifically mentions it, but the methodologies sound pretty much like what I do now.

Thanks anyway -

[johnruffing]

I can confirm that when I asked the same question, no "survey mode" exists on the AIR-LAP1131AG or AIR-LAP1242AG.

That said, you can convert these APs to autonomous mode (there are a number of threads on this forum that discuss how to do this). After you are done with the site survey you can flip the APs back.

From the Cisco "Wireless Site Survey FAQ - Document ID: 68666"

"Q. Can I perform a site survey using Cisco Aironet 1131 and 1242 access points and then use the results to deploy an Airespace wireless solution?

A. Yes, you can do this as long as a proper site survey is conducted and the results yield an effective Wireless solution. In this case, you can use any site survey tool."

If you intend on carrying your RF settings manually once deployed using the WLC, you will need to refer to the following document which correlates autonomous power settings (in dB) to the WLC power setttings 1, 2, 3, etc.

Excerpt from WLC Configuration Guide v4.0:

"The transmit power level is assigned an integer value instead of a value in mW or dBm. The integer corresponds to a power level that varies depending on the regulatory domain in which the access points

are deployed. The number of available power levels varies based on the access point model. However, power level 1 is always the maximum power level allowed per country code setting, with each successive power level representing 50% of the previous power level. For example, 1 = maximum power level in a particular regulatory domain, 2 = 50% power, 3 = 25% power, 4 = 12.5% power, and so on.

Note: Refer to the hardware installation guide for your access point for the maximum transmit power levels supported per regulatory domain. Also, refer to the data sheet for your access point for the number of power levels supported."

Final thought: I have found that the AUTO RF tends to work better if you start out your APs with manual channel settings from your site survey and then release everything to AUTO RF at the same time. The automatic channel choices that the WLC comes up with are not optimal.

The steps to doing this are:

1) Changing the global AUTO RF setting to manual channel selection or ON DEMAND. Power setting can stay on automatic.

2) Change your APs to the manual settings from your survey.

3) Change the APs to automatic RF settings. (They will not change until AUTO RF channel selection is re-enabled.)

4) Re-enable AUTO RF channel selection.

This is not official from Cisco, simply based upon my own observations. However, my experience so far has been that the channel settings I pick tend to work better (I see higher power level settings on the APs since they have less co-channel interference) and WLC will continue to use the manual channel settings unless the some significant outside interference is encountered.

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- John

[john.preves]

Thank you, this is the scenario I was kind of afraid of.

If I just spent 2 months conducting a thouroughly exhaustive survey to determine how large my cells can be so I can physically load balance my network and provide aggregate throughput across the infrastructure; I can now plug all this carefully collected data into this idiot box and pick my power settings 1-4?

Am I wrong to think this utensil is so marginally talentd people can roll out marginally useful WLAN's?

What happens to my cells that I designed at 5mW? Do I just get to come close now???

When the power decides to be increased to fix a hole from an AP going bad (how bout just making AP's that don't go bad???)what takes into consideration the negative effects of bumping up the power in a given environment thereby causing all the clients to associate to one or two AP's and leave the others under-utilized?

I will read some more about this but the only way I see this being of any use at all is if you can turn off the "magic" and set it once and use it as is.

Thanks for your reply bro - I gave you a 5...

[johnruffing]

You're welcome.

However, I do want to clarify a few points:

1) There is a direct correlation between the power settings 1, 2, 3, etc. and the actual milliwatt/dbi output. So you should be able to recreate the settings from your original design.

2) I think that you will find the overall reliability of the APs to be quite good.

3) You will need to decide if it makes sense to give up some of the special adaptive features that the WLC offers (automatic channel adjustment for interference avoidance, and "self healing" RF.) Setting the channels manually will override these functions. Personally, I'm not sure that I'd be in a hurry to give those up, but you know your environment best.

4) Keep in mind that, in the unlikely event of AP failure, the RF settings will return to normal once the AP is replaced.

5) I would like to also point out that, unless the environment is especially challenging, Cisco typically recommends letting the system run on full AUTO RF and adjust itself.

6) The workaround process that I described earlier has been a way to help the system pick better channels if you are not happy with the automatically selected ones. I have requested a Product Enhancement Request that would permit the system designer to specify a "preferred" channel that could be used initially by the WLC (and would be based upon the original design/survey). This would not lock the channel manually (as is possible today) but would give the WLC a better starting point. This feature would also prevent having to perform the workaround process referred to earlier. We'll see what Cisco has to say on the idea.

Finally, you might want to see how the product performs in AUTO RF mode in your environment and then decide if you need to make manual adjustments (or make a temporary channel "suggestion" to the WLC by setting a channel manually and then back to automatic) - if needed.

- John

[johnruffing]

Afterthought:

I supposed it would have been nice to include a reference to the actual document (that I referred to in item 1 above) that correlates the LWAP/WLC 1,2,3,etc. power settings with actual power settings on the autonomous AP in dBm.

(To convert from mW, you can reference the GUI on the autonomous AP and I believe there is a chart there)

This document was EXTREMELY helpful when I was surveying with an Autonomous AP and wanted to know corresponding WLC/LWAP power settings when I deployed later.

Here is the link:

http://www.cisco.com/application/pdf/en/us/guest/products/ps6707/c1099/ccmigration_09186a00807159ef.pdf

I hope this helps,

- John

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[cisco_designer]

Dear John,

One of the purpose for doing a site survey to explore how many access point do we need in this site. Therefore, a third party is recommended (AirMagent Products)

http://www.airmagnet.com/

Regards,

[john.preves]

Thanks, but I am not a big fan of Airmagnet to do surveys with. Airmagnet laptop is a wonderful tool to help troubleshoot an existing issue in an existing infrastructure or detect rogue AP's, but the survey tool among other things, hangs and you have to restart the program to get it to function. Plus, Airmagnet will not be the application in use when the network is completed, so I see no reason to base my survey without using the devices that will be used during production. Phones should be surveyed using at least a phone...preferably voice and data should be surveyed with the card that will be in use. I still like the free Cisco tool to be honest...

[johnruffing]

John:

We have used Ekahau Site Survey on a tablet PC and it has worked really well.

You scan in a JPEG graphic of your floorplan(s) and then tap the screen to indicate where you are on the floorplan and (as long as you walk at the same speed between locations) Ekahau will interpolate all the readings measured and plot them on the floorplan.

The color reports show RF signal strength, signal to noise ratio, AP location estimates, etc. all plotted on top of the floorplans.

I don't mean to be "selling" you on the product here - we don't sell the product - we just use it for our RF surveys and it has worked quite well.

http://www.ekahau.com

Hope this helps...

- John

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[john.preves]

I should disclose here that I have 8+ years experience designing and implementing wireless networks and I can say that in the last 5 years I have been doing them correctly.

I have seen the Ekahau product and while I would still do the physical survey anyway, I see the benefit of mathematically tuning your survey based on actual numbers compared with the projection model. This in my opinion would be the most accurate way of doing it, but most people won't pay for that.

I'm just not sold on the idea of spending the time and effort to discover any interference, design around the parameters you are given, come up with a workable solution, install it turn it on and certify it; only to walk away and let this thing do whatever it wants. My designs usually work when I turn them on, I'd rather like to keep it that way.

I will have a look at the link you posted, thanks. All info is good info.

[john.preves]

After reading the link I think I will like this arrangement better, as I am rarely interested in the maximum power but usually the other way. I can split hairs even more now it seems.