Wireless Access

Hey everyone,

We have a customer location running 8.3.0.5 AOS with a physical controller and Mobility Master. AP model 325.Most configuration was done following the roaming AC vrd guide. 4 SSIDs, reduced power for 2.4, removed lower connection speeds, etc.

 

The issue is that there are a few specifc devices that when active generate alot of retransmissions and cause channel utilization to go 90%+, usually creating a domino effect and taking other users with them. We were able to isolate a single PC which uses Realtek wireless (b/g only). Even after upgrading the device driver, the issue remains.

 

This was tested in an empty office, single device on the AP, download was going at 4 Mbs, drops to 700 kbps.

 

A site survey was performed (Ekahau) and there was no outside interference to justify this.

 

How can I find out what is causing the retransmissions? Should I wireshark at the controller? The retransmissions are only from AP to client, and not the other way around. Any ideas on what could be causing this?

 

Right now the action plan is to rollback to the conservative release...

 

Thanks!

RK

It is quite possible that the power is too low for that client, and it cannot hear the AP.

Thanks for the reply. We tested the device at less than 2 meters from the AP and had Ekahau next to the device. Reception was fine. We did reduce the retries to on the VAP profile to 2, that decreased the channel utilization and maintained the download rate at ~4 Mbps. It seems like the AP is retransmitting without reason....

You should do a wireless packet capture on that channel to see if you can get a clue what frames are being retransmitted and what other frames are in the mix.  It is possible that another device is participating or contributes to the retries (cochannel interference, maybe).

 

When you say Ekahau, do you mean the site survey or the spectrum software?

We are using the Ekahau sidekick, so we could see both spectrum and co-channel interference.

 

We planned on doing the packet capture, just curious if you recommend packet captures at the AP (ap packet-capture) or controller (datapath) levels?

 

Thanks,

RK

I will say ahead of time that I don't have any experience with Ekahau Spectrum with the sidekick.  EDIT: If there is co-channel interference, it is probably a combination of too many SSIDs and 2.4ghz transmit power.

 

Taking a step back and looking at your original post, you said that there is high utilization when this client is active.  Where do you see that there is high utilization and is it sustained?  What applications does the device use?  What are the RF capabilities of the client's adapter?

Just as future reference, this has been identified as a firmware issue and is resolved in future releases. Specific to this AP model I believe. Thanks for all the input! RK