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Introduction

Updated 6/15/2009: Clarified Source tagging requirements.

In Part 1, I provided some background on WMM and showed the client and AP controls that enable it. And in Part 2, I actually managed to show an example of WMM properly prioritizing media traffic. In this final Part 3, I'll show additional test results and to wrap things up, explain why WMM doesn't currently provide any improvement for media streaming.

Vista and qWave

On the road to finding the combination of router, clients and settings that worked, I kissed a lot of frogs. And once I had a "known good" IxChariot script, I tried some other variations.

I first tried just reversing the traffic flows of the test pairs to test whether WMM worked running uplink. The plot in Figure 1 first fooled me into thinking that uplink WMM wasn't working, because the "background" trace didn't fall below the "Video" trace when it started.

Uplink not working?
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Figure 1: Uplink not working?

But upon closer inspection, the "Video" stream is getting its required 10 Mbps of bandwidth and the "background" stream does drop its speed a bit. It turned out that I was just fooled by the higher bandwidth available running uplink. Once I raised the BK stream rate to 20 Mbps and the VI stream to 15 Mbps, I got a clearer indication that WMM was working fine, as shown in Figure 2.

Uplink WMM clearly working
Click to enlarge image

Figure 2: Uplink WMM clearly working

I next tried using the Intel WiFi Link 5100 AGN client in the notebook running Vista SP1. Vista supports an "improved" QoS scheme called qWave (Quality Windows Audio-Video Experience). Neither the Wi-Fi Alliance WMM white paper nor the test plan mention qWave. But my Ixia contact said that it should support WMM without having to perform the registry change needed on XP.

So I switched in the Vista SP1 notebook as an endpoint for the VI ("video") priority stream. And it worked just fine as shown in Figure 3 and also running uplink (not shown).

qWave in Vista SP1 works fine
Click to enlarge image

Figure 3: qWave in Vista SP1 works fine

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