QoS on Centralized WLAN clarification

[jlarriega]

Good Day Experts;

I like to get some clarifications on how a frame received by the AP from a non-WMM client is forward to the WLC.

A non-WMM client doesn't have 801.11e UP or DSCP(?) value present on the frame from a non-WMM client to the AP but I read the AP will write the default DSCP value of the QoS WLAN profile. Does it mean that I connect to a Voice WLAN using my laptop and I will get a DSCP value of 46 and COS priority 5 on the switch connecting to the WLC?

Thanks;

 Juan

[Scott Fella · Accepted solution]

No... If your device is non-WMM, the traffic from the device to the AP is best effort. Now if your application tags the traffic, then the AP will respect that marking and will send it with that tag as long as the WLAN allows that marking. The WLAN QoS will cap the WLAN's QoS value. So if the WLAN is set to Silver and you have voice traffic, the highest marking would be that of Silver. 

-Scott

[Scott Fella]

Take a look at Rasika's blog:

http://mrncciew.com/2012/11/28/understanding-wireless-qos-part-1/

-Scott

[jlarriega]

Thank you Scott for your prompt reply.

I don't know if you have the Cisco Press book "End-to-End QoS Network Design" by Tim Szigeti, on Page 400 says what you mentioned on your response to me but on the same book on page 402 reads "If the wireless client doesn't support WMM,.... the default 801.11e UP value for that WLAN is used in the upstream mapping"  which I read it as a contradiction to the statement on Page 400.

Thanks Scott, I look forward to your response to what I think it is a contradiction.

[Rasika Nayanajith · Accepted solution]

Hi

"If the wireless client doesn't support WMM,.... the default 801.11e UP value for that WLAN is used in the upstream mapping"

This is accurate when non-WMM clients upstream traffic up to certain code of WLC. I have tested this with 7.0.116.0 code by disabling WMM & inspect the packet captures (since I could not find non-WMM client for testing). See below for detail.

http://mrncciew.com/2013/07/30/wmm-qos-profile/

Since this non-WMM traffic get higher priority (if QoS profile is Plantinum or Gold) Cisco introduced a way to change that behavior (i think in 7.4.x onward). "Unicast Default Priority" & "Multicast Default Priority" settings shown below is used for that purpose. If you configure that to "Best Effort" all non-WMM traffic classified as Best Effort (in previous codes all non-WMM traffic mark as QoS profile value configured)

Here is a Ciscolive presentation (delivered by one of the author of End-to-End QoS book you mentioned) that you should not missed. I have taken the above slide from that presentation.

BRKRST-2515 - QoS Design for Wireless LANs (2014 San Francisco)

If this is not clear let me know. I'll try to explain it further

HTH

Rasika

[jlarriega]

Thank you Rasika and Scott - Your explanation is very clear as always.

Rasika congrats! on your new CWNE, you can write a book about wireless now. 

Happy New Year to all of you Experts!

Juan

[Rasika Nayanajith]

Thank you & wish you a happy new year too.

Rasika

[shh5455]

Rasika,

That slide shows that setting the default priority for unicast traffic sets the maximum priority for BOTH WMM & Non-WMM traffic.  Have you found something else from your testing?

Thanks

Steven

[Rasika Nayanajith]

Hi Steven,

I haven't done much testing with this. But this is how I interpret it.

Maximum priority is the capped value for WMM traffic (ie frames comes with UP value). Eg. If you configure "Gold" for this, if voice packets comes with UP=6, then AP map outer CAPWAP to AF41 for those. (not EF)

Default priority is for the non-WMM (or frames come without UP) traffic.

HTH

Rasika

*** Pls rate all useful responses ****

[shh5455]

I see what you are saying and I hope that's how it works, but the slide seems pretty clear that you are setting the max priority for WMM AND Non-WMM traffic.  It would be much more useful the way you are suggesting.

I have a customer who is starting to use Jabber for Windows for phone calls.  I want to move them towards setting the SSID to WMM-Required.  In the interim however, I want to make the SSID Platinum to ensure QOS for the voice calls.  Unfortunately, this will also make non-WMM traffic EF as well. 

Maybe there is a clever way to classify the Jabber traffic with AVC and mark everything else best effort, but I haven't seen it.