PC + Softphone over WLAN QoS

Unanswered Question
Jul 10th, 2012

I could not find after hours of searching what Cisco’s best practice when using a PC and softphone in a wireless environment.

We have always had wireless phones in one WLAN (platinum) and PC in another WLAN (silver). But now we have PC + Softphone scenario which is growing

Do we now put all PC's into the voice WLAN (hundreds of users) which is setup as Platinum and mark the voice traffic from the softphone DSCP 46 (maybe 48 because of WMM and COS mapping) and everything else from PC mark as best effort?

If WMM is turned off on the PC will the AP then treat all traffic as Platinum level regardless of DSCP marking.

If I leave the users in the Silver WLAN then all traffic will get marked down to best effort.This is current setup and voice quality is suffering.

I don’t feel comfortable putting hundreds of users on a Platinum level WLAN but how else can I prioritize softphone voice traffic. What are the implications of putting pc + softphone users into the voice wlan? What does cisco recommended for this scenario?

if you have any insight/experience/documents please let me know

Thanks!

I have this problem too.
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Amjad Abdullah Tue, 07/10/2012 - 12:27

Steve,

Softphone over wireless is not supported by cisco. I know that cisco TAC does not support this scenario.

I've seen data wlan on gold profile that works fine with softphone over wireless though

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grabonlee Tue, 07/10/2012 - 16:54

Steve,

What softphone application are you using?. The best way to go is not to only treat all traffic as platinum but have a switch that is able to trust dscp packets that it sees on the port. Also remember to enable 802.1p on the controller. You can also mark QoS specifically on Windows 7 clients through gpedit for the client only or Group policy objects in your domain for all clients. After doing so, I would suggest that you run wireshark trace or any other monitoring tool to see if the voice packets are marked appropriately. To run a trace, I would prefer that you do SPAN on the VLAN and not the wireless client.

Softphone over wireless is really a gray area but is achievable and depends on a lot of factors such as proper AP placement. This is because excessive roaming can affect voice irrespective of the priority given to voice packets.

Cheers

Amjad Abdullah Tue, 07/10/2012 - 23:47

steve sousa wrote:

Do we now put all PC's into the voice WLAN (hundreds of users) which is setup as Platinum and mark the voice traffic from the softphone DSCP 46 (maybe 48 because of WMM and COS mapping) and everything else from PC mark as best effort?

If WMM is turned off on the PC will the AP then treat all traffic as Platinum level regardless of DSCP marking.

WLC does not do anything to the QoS on the packets it forwards except the translation between 802.11e ot 802.11p.

If you have clinets that are connected to a Platinium profile but they use normal DSCP (data. No priority) the traffic will be treated normally as data with no priority.

If another WMM enabled client connected to the same WLAN and send voice traffic with platinum profile, the traffic will be mapped to the appropriate 802.1p and will pass the wire with priority.

The controller does not apply its own QoS. The QoS support on the WLC gives the WLC the ability to apply the same priority that is set on the wire (or application).

Therefore, the only action a WLC or AP will do is copy the value of the original packet to the outer header of the LWAPP packet. The whole purpose of the gold, silver, and bronze QoS options on the WLC is to perform proper QoS translations between 802.11e/802.1p UP values and IP DSCP values, which depend on the application or standard that is used. Once again, QoS on the WLC ensures that packets receive the proper QoS handling from end to end. The controller does not perform its own QoS behavior. The support is there for the controller to follow suit if QoS already exists and priority needs to be applied to wireless packets.You cannot have QoS only exist on the controller.

Reference: http://www.cisco.com/en/US/tech/tk722/tk809/technologies_configuration_example09186a00807e9717.shtml

Also;

Note

WLAN client support for WMM does not mean that the client traffic automatically benefits from WMM. The applications looking for the benefits of WMM assign an appropriate priority classification to their traffic, and the operating system needs to pass that classification to the WLAN interface. In purpose-built devices, such as VoWLAN handsets, this is done as part of the design. However, if implementing on a general purpose platform such as a PC, application traffic classification and OS support must be implemented before the WMM features can be used to good effect.

Reference: http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob41dg/ch5_QoS.html#wp1021909

HTH

Amjad

George Stefanick Thu, 07/12/2012 - 06:27

Steve,

Cisco and QoS wireless is one of those things I would like to call "dazed and confused"... Bill Cox, from Cisco once said, "When I thought I knew QoS, I get asked a questions, which makes me wonder. Do I really know wireless QoS".

Jerome Henery has a multi part video on you tube which is great,  below is a link.

http://www.youtube.com/watch?v=44t-0JYEwkA&feature=plcp

As for QoS, you have 2 parts, wireless and wired and they both have their own rules and behavior. In short, if you have a data laptop connected to SILVER (DATA QOS), and you want to add a soft phone and you want PLATINUM (VOICE QOS) you need to add that device to a SSID supporting PLATINUM.

Amjad Abdullah Tue, 07/17/2012 - 22:53

George:

Thanks for Jerome links. I was too lazy to watch any but now I watched the QoS part. +5.

Jerome is really amazing. I would say he is number 1 in sharing such useful information for wireless (CCIE wireless in specific).

Just like you said, for voice clients one needs Platinum QoS. I just want to clarify a point to Steve that he needs WMM capable client. That will make the traffic priorirized from it is origin (WLAN adapter). i.e. data sent with data priority and voice sent with voice priority. in this case if the QoS of WLAN is platinum, the data will be treated as silver and voice will be treated as platinum.

If the WLAN has Silver QoS profile, then all traffic will be sent to the wired as silver (translated to the wired equivalent QoS method) although the client may originate the ovice traffic as platinum but the WLAN profile allows only to Silver max so it suppresses the QoS info.

George Stefanick Wed, 07/18/2012 - 20:03

I agree with your statement, but you confuse me with the bronze comment and then you jumpped to silver. But, yes that is how I understand it as well. The WLC will never mark up, but will mark down.

Amjad Abdullah Thu, 07/19/2012 - 01:10

Sorry!! I meant silver, not bronze. Corrected.

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George Stefanick Thu, 07/19/2012 - 05:42

So in short you need to add your client to the highest QOS level and let marking happen down wards. However, there is a problem, when you do this, on the wireless side you will be giving shorter NAV timers to DATA clients WHICH will compete for the same air time as voice.

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Posted July 10, 2012 at 11:55 AM
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