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Wireless Interferance

ciscoscott2012
Level 1
Level 1

Hi All,

We have recently deployed a new WLAN for voice but we are expereince poor voice quality with stationary devices, voice is fine when connected to the LAN. This is happening on both 2.4 and 5 GHz frequencies.

We have followed best practise to disable lower data rates and QoS etc. There is lots of packet loss in the direction of AP -> client but call quality is clear in the directtion from client -> AP.

The deployment is quite dense using 3500 series clean air access points roughly 35 feet apart. Looking at the 5Ghz range on one of the problem access points, it is on channel 40 reporting no interferance on the same channel and 2% utilisation. Clean air reports no interferance and 100% Air Quality. The AP does report interferance of -78 dB on neighboring channel 64 with 50% utilisation. Will neighbor channels cause any issues? I also notcied alot of output queue drops on the dot11radio1 on the AP which is constantly increasing but there is no apparant packet loss when sending pings with 200 byte packets to the connected clients.

9 Replies 9

Scott Fella
Hall of Fame
Hall of Fame

Take a look at this document if you haven't seen it. This doc explains what code version (1.4.3) to use and other important facts that you should know about. If everything is setup like what the document states, then give us more info on what you notice with wireless voice calls.

https://supportforums.cisco.com/docs/DOC-26863

Sent from Cisco Technical Support iPhone App

-Scott
*** Please rate helpful posts ***

Hi Scott,

Thanks for this.

Our depolyment actually uses Cisco IP Communicator and Personal Communicator on laptops. I'm hearing and seeing packet loss on calls (also traced in wireshark) in the direction from our voice gateway to our client devices so AP to client.This happens on different bands and on aps that only have 2 or 3 devices associated. This also happens on a mix of intel and broadcom wireless NICs.

Is there anything else that I need to be aware of in this typeof deployment?

Wish Cisco had a way to QoS applications. See one of the problems with this is you are fighting for other data QOS wise. When the 2 get mixed it adds complexity.

Scott is on to something with the clients. if I were you try and set one of each device you standardize on, and test each one side by side. It already sounds like you did a lot of home work already. But this sounds to me to be a client issue.

__________________________________________________________________________________________
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin

"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin
___________________________________________________________

Scott Fella
Hall of Fame
Hall of Fame

Well that's a bit more difficult. I know that on the intel 6200 adapters with firmware 14.x, we had issues with 40mhz so we left it at 20mhz. v15 on the intel fixed the issue on the 5ghz. We had an issue with some Broadcom and the fix was also driver related. Can you review the drivers and test. Are you doing any QoS? I'm assuming the data and voice is on the same QoS level since your using wireless.

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-Scott
*** Please rate helpful posts ***

Interesting about the drivers. As its voice we are only using 20ghz on both 2.4 and 5.

Yes qos on the LAN but WLAN is challanging as we have both voice and data over the same WLAN. We knew that there would be some issues but not as aggresive as what I'm experiencing.

Are there any specific wlc config options I need to be using?

I'm thinking that heavy interference could cause this but I'm not sure how to translate the ap stats. I can't see anything obvious especially on the 5 ghz

Here is the thing also... How are you applying QoS on the wired side when a client has a soft phone? If you sniff the traffic on the wired side, do you see the VoIP traffic tagged both ways? Wired and wireless is different but the OS (windows) you need to be able to have the OS tag the packet or else the ap will be sent as data traffic.

Here is something that is a good read:)

http://revolutionwifi.blogspot.com/2011/09/microsoft-lync-qos.html?m=1

Sent from Cisco Technical Support iPhone App

-Scott
*** Please rate helpful posts ***

Thats a good point, just checked and it appears that the OS isnt tagging packets correctly as they are sent from the host, receive traffic is fine.

However, my issues is only on traffic being received from the AP so I dont think that this is the cause. Also, I have tested with a couple laptops isolated to a few APs running nothing but voice and I still experience the issue.

Noticed on the radio interfaces that output drops and constant although I dont see any drops when I ping the wireless clients using small and large packet sizes from our voice gateway. What causes output drops on the APs? The APs are connected as Flexconnect, could this be causing the issue?

Your help so far is really appreciated.

Saravanan Lakshmanan
Cisco Employee
Cisco Employee

Are DTPC enabled on the network. Try testing by enabling and disabling it.

Be sure wmm enabled on the data pc.

what's continous RTT btw clients.

DTPC is enabled, I will try disabling on the WLC.

WMM is enabled on the client although I disabled on the WLAN as it caused RTT of + 100ms between the clients and a device on the local LAN, switching WMM off reduced RTT to avergae 2ms

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