As stated in my previous wireless QoS posts, it is purely up to end device to correctly classify traffic within the wireless media. AP does not have control how end devices tagging user priority (UP) in 802.11 frame. AP simply use this UP value in 802.11 frame to map QoS values in CAPWAP headers and subsequently this will determine how packet will get QoS treatment within wired media.
If end device (BYOD) is WMM certified we would expect that to classify traffic into one of Voice, Video, Best Effort, Background classes and tag correct UP value in 802.11 frame. But in reality it will not work as we expect. Some time application developing vendors & BYOD manufacturers are not collaborative (as they are competing for same market segment).
I have made a call from wireless device to wired phone & capture packets at 3 different location shown as “A” “B” & “C” in the diagram. I have mentioned the device type & operating system used as things heavily depend on hardware/driver platform & operating system used.Also shown the 802.11 band where the end device associated. WLAN configured with Platinum QoS profile & WMM settings as “Allowed”.
Here is the result for wireless phones. You can see Cisco wireless phones mark UP value 6 for its voice traffic & UP-4 for its signalling traffic. iPhones mark voice traffic with UP value of 5 (treat as video), but signalling traffic go as UP-0. Galaxy SII mark voice traffic as UP of 4 & signalling traffic as UP of 3.
If you look at Tablet devices observation is quiet different. Most of the apple devices does not correctly classify traffic with required UP value. In this case no prioritization within the wireless cell & further in wired media as well. All type of traffic go as “Best Effort” in to wired media. Noticed SIP traffic mark as CS3 in original IP header, but no UP other than “0″.
As you can see behavior is different in each type of BYOD and you need to verify end to end QoS can be delivered prior to deploying voice/video services over wireless network.
To overcome this issue (BYOD does not classify traffic properly) cisco has come up with traffic classification (feature called Application Visibility & Control) in 7.4 software release for WLC. In this way at least traffic can be re-classified at the WLC, so wired media will get correct QoS treatment for the different type of traffic. Still this won’t help to prioritize upstream traffic from wireless client to Access point. That’s why you should select appropriate BYOD models to deliver voice/video services over wireless.
I Will write another post on AVC feature in this WLC 7.4 code.