In this post we will see the impact of enabling or disabling WMM (Wireless Multi Media) to QoS of wireless traffic in a given WLAN.
WMM setting is based on IEEE 802.11e standard to provide QoS to wireless network. An 802.11e (or WMM) client that obtain medium access must not utilize radio resources for a duration longer than specified limit (called transmission opportunity or TXOP). Also WMM client will classify their traffic in to four access classes (AC_VO, AC_VI, AC_BE & AC_BK). Below diagram show the difference with legacy system & WMM capable system.
Ref: Analysis of IEEE 802.11e for QoS Support in Wireless LAN
Here is the topology for our post. Wireless Phone is connected to a WLAN configured with Platinum QoS profile. Traffic flow “D” & “E” will be looked at in detail for QoS analysis while WMM is enabled & disabled on this WLAN.
Here is the basic WLAN configuration
(4402-3) >config interface create vlan1 1 (4402-3) >config interface address dynamic-interface vlan1 192.168.2.249 255.255.255.0 192.168.2.250 (4402-3) >config interface dhcp dynamic-interface vlan1 primary 192.168.2.250 (4402-3) >config wlan create 1 ONE ONE (4402-3) >config wlan interface 1 vlan1 (4402-3) >config wlan radio 1 802.11a-only (4402-3) >config wlan security wpa disable 1 (4402-3) >config wlan qos 1 platinum (4402-3) >config wlan wmm require 1 (4402-3) >config wlan enable 1
Here is the QoS settings in GUI if you are familiar with it than CLI.
In this configuration we have restricted only WMM capable clients can join to this WLAN (by selecting WMM require option). WLAN is configured for Platinum profile where upto CoS =5 (or DSCP EF) QoS is allowed.
When 7921 phone make a call to 7965 phone here are the two different type of traffic (signalling – SCCP & media – RTP) wireless frame captures.
When AP receive these frames it will convert 802.11e priority value to CAPWAP header DSCP values. Since we have configured Platinum profile it will allow upto 802.11e priority value of 6. So in this case Voice traffic CAPWAP header DSCP would be EF & Signalling traffic CAPWAP header DSCP would be AF31 (as per the 802.11e to AVVID 802.1p mapping table). Below captures taken at AP connected switch port (Fa 1/0/4) prove this.
As long as you trust DSCP on AP connected switch port(Fa1/0/4) & CoS on WLC connected switchport (G1/0/1), this traffic will go to wired network with CoS=5 for voice & CoS=3 for signalling traffic.
Now let’s disable WMM on this WLAN & see what impact it would do on the traffic QoS. You can disable it via GUI or CLI & here is the CLI way of doing that.
(4402-3) >config wlan disable 1 (4402-3) >config wlan wmm disable 1 Warning: 802.11n requires WMM to be enabled (4402-3) >config wlan enable 1
As you see above this will impact the 802.11n functionality. If you disable WMM on a WLAN client won’t get 802.11n data rates.
Once WMM is disabled, AP is not negotiating any WMM settings and client wireless traffic comes without any WMM priority information. You can see both SCCP & RTP traffic wireless frames no WMM information available.
Since no priority values comes in wireless frames ALL traffic will get the QoS profile’s DSCP/CoS value in this time. So both traffic will get DSCP EF in CAPWAP header & translated into CoS of 5 prior to send to to wired network by WLC. So in this time all traffic coming from wireless client will mark as EF. Here is the capture of AP connected switch port.
Therefore it is important to understand this difference when you configuring QoS profile & WMM settings.
When enabling WMM there is another option called “WMM Allowed”. In this scenario it will allow both WMM capable client & non-WMM capable client to join the WLAN. But all non-WMM client traffic will mark as per the configured QoS profile.
Related Posts
1. Understanding Wireless QoS – Part 1
2. Understanding Wireless QoS – Part 2
3. Understanding Wireless QoS – Part 3
4. Understanding Wireless QoS – Part 4
5. Understanding Wireless QoS – Part 5
6. 3750/3560/2960 Wired QoS
7. Who do you trust ? (DSCP or CoS)
8. BYOD with QoS
9. QoS for H-REAP
10. VoIP Phone – Switchport Config
11. Autonomous AP – QoS
12. AAP QoS – A Closer Look
13. A Wireless Bridge with QoS
mrn-cciew 
Reblogged this on ytd2525.
great post and great blog but I have one comment: The last sentence “But all non-WMM client traffic will mark as per the configured QoS profile.” is in my opinion wrong.
I’ve tested this in my lab with non-WMM client and set WMM profile to allowed and there is not marking according to the QoS profile. This does only work when I set it to WMM disabled. Tested with controller 7.5 release.
Hi Roger,
Thanks for the feedback, what was your WLAN QoS profile set to (bronze, silver, gold,platinum) when you did your testing.
When you upgrade to WLC 7.5, did you notice QoS profile is 802.1p value is changed to a wrong value by default CSCui69732 (ie platinum – 802.1p to 5, Gold 4 etc) where it should be platinum 6, gold 5, etc.
I have done my testing on 7.0.116 which was the wireless lab software version. I will do a test on 7.5 & confirm this
Regards
Rasika
Hi Rasika,
I’ve set the profile to platinum and tested with the iPhone 4s as a client, doing some webbrowsing. Had the AP directly connected to a switch where also the WLC is connected. Created a monitor port, capturing all traffic of the port where the AP is connected.
Rergarding the bug, thanks for that hint, I’ve seen the change on a customer network but I did not know that it was a bug. Now I have the explanation 🙂
It’s anyway “a shame” and very very confusing for most of the customers that in the WLC they write “wired QoS dot1q” but then you have to set the IEEE 802.11e value, which is shifted by 1….however 🙂
regards
Roger
Rasika,
Did you already find time to test the “WMM disabled” case?
regards
Roger
Not yet, I hope I could do it within next 2-3 days, I will update you
Hi Nayarasi! Congratulation on your recently CCIE Wireless.! As you might noticed I follow your blog and I’m also taking lab for CCIE-W. I have one question in regards for WLC QoS profiles, Wired QoS protocols 802.1p tag values. For example: Platinum, default value is 6 (48 CS6), is it recommended/best practice to change it to 5 (46 EF)? same for other profiles?
Regards
Jose T Perez
Date: Tue, 30 Jul 2013 12:16:04 +0000 To: jose_tomas_perez@hotmail.com
Hi JT,
Do not change this value. You should think of this is 802.11 frame UP value (mean if wireless frame come with UP value of 6 it will treated as Platinum traffic)
Leave it for default values when configuring QoS profile. ie Platinum -6, Gold 5, Silver-3 & Bronze-1
HTH
Rasika
Hi Rasika,
I’m little bit confusing regard QoS profile. You tell us to leave the default value but now I’m reading the “Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Deployment Guide” page 81:
QoS Profiles
Configure the four QoS profiles (Platinum, Gold, Silver, Bronze), by selecting 802.1p as the protocol type and set the 802.1p tag for each profile.
• Platinum = 5
• Gold = 4
• Silver = 2
• Bronze = 1
Can you help me?
Thanks!
Giovanni
Hi,
When configuring 802.1p value on WLC, you have to you have to go with default values (6,5,3,1) & you can think of this is equivalent to 802.11 frame UP values
Regards
Rasika
HI Rasika
How did you get your EAP-TLS working in the LAB?. There is no CA provided
regards
Joe
That’s should be there…
Does a client that is configured in 11AX mode will connect with AP which has WMM-PS (UAPSD) and WMM both disabled configured in 11ax mode? I tried this experiment and saw that client does not connect at all both in 2.4Ghz and 5Ghz. Can you please clarify why is it like this?