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Hi All,

We recently had a 3rd party complete an AirMagnet site survey of a WLAN we've deployed. The wireless implementation is fairly straight forward; we have an 802.11G network with Cisco AP's controlled by a WLC. We provide two WLANs, one for corp devices and another for guests, each WLAN has its own SSID which is not broadcast.

In summary the survey showed we had good coverage but had a fair bit of co-channel interference too.

I've since visited the site and as far as I can see I???¡é?¡é?????¡é???¡ém not seeing the co-channel interference they showed in the survey. To be fair I???¡é?¡é?????¡é???¡ém not using AirMagnet, rather I???¡é?¡é?????¡é???¡ém visiting each room in the building and checking how many AP's i can see in that location and which channel they are on using the wireless NIC client utility that came with the laptop (i know this isn't really best practice but its all i can do!!). In the vast majority of occasions I???¡é?¡é?????¡é???¡ém seeing 3 AP's all on different channels, although sometimes 4-5 AP's with the 4th and 5th at very low signal strengths. So it appears to me that the RRM on the WLC is doing its job well.

So my question for people who know something about AirMagnet site survey is... could the co-channel interference shown in the report simply be the 2nd WLAN being broadcast from each AP? Does AirMagnet show 2 AP's detected for one physical AP if you have 2 WLAN's setup? - and if so, could it see one as interfering with the other because it doesn't know they are physically the same device?

Thanks for any help.

Neil

The co-channel screen (airwise) or the main display screen will show the multiple WLAN's as additional channels that can be scored as co-channel interference. so they could just disable those for the scoring/validation (extra sequential mac addy's from each additional wlan profile.)

matt

Hi + thanks for the info.

Am i correct in thinking then that if you weren't to exlude either all of the AP's for one of the WLAN's that could show as bad co-channel interference?

If both the corp and guest WLAN's aren't broadcasting their SSID's and AirMagnet shows the SSID's as "unknown" would the only way to identify the AP's to disable for scoring/validation be via the squential mac addresses?

Thanks,

Neil

you can probably get a display only version of the s/w and play with their survey. otherwise, yeah those other aps show as interference.


if no broadcast, and no probe response with ssid elemenet then you would either have to sort by mac or just name them using airmagnet.

You need to turn on 'AP grouping' to make sure a single AP, with two distinct MAC addresses (one for each SSID) are 'grouped' as only a single device.

Then you are asking AirMagnet to compare same channel interference with only the other devices on the same channel, and not the other MAC addresses on the same channel (the 'extra' virtual MACs to support those two SSIDs)

That should solve your problem.

Or... just turn off (un-check) every other MAC address
Or... even easier, just analyze ONLY one SSID at a time

Coverage is usually very easy to achieve. But getting rid of co-channel interference (read collision domain) is the real bugaboo in WLANs.

Good luck on your project. If you have any further AirMagnet Survey questions - feel free to ask away!

Keith

Thanks for the info! :D

Neil

word up Keith, you are still a great mentor! i was going to then reply with the ap grouping option to faciliate the option of multiple SSIDs (virtual mac addys)! i remember i think it was '05 when you challenged our group @ cap1 to figure out why there were multiple macs under that 2.4/5Ghz display screen.

'Hello World' Keith is a great teacher!

Matt

Keith,

I currently use our WCS to provide me with a CSV file of our inventory of access points which I save as a text file to import into AirMagnet WiFi Analyzer.

I have tried using AP Grouping in the past, and it did not work. We have over 1000 access points, all broadcasting between two and four SSIDs.

We have a programmer who wrote up a little PERL script that expands the MAC-to-hostname file into sixteen MAC addresses mapped to each AP hostname. We then import that into our WiFi Analyzer. Lately the importing has been bombing when we try to import the list since it's rather large.

Reading this post, it has renewed my interest in AP Grouping. I definately do not want to go in and configure AP Grouping manually - with over 1000 access points that would take a long time. We're constantly adding more - about 25 this week, so it's an ongoing process.

Do you know of an "automatic AP Grouping" function that will make this easier?

And even better, do you know if I can import that list into our Survey Pro?

Thanks,
Tim

-Sent from my Cray-1.