A-MSDU Priorities?

[IT Services]

Hoping someone in the community can help explain the 802.11n packet aggregation configurable priority values on a Cisco WLC based environment. Do these priority values correlate with QoS (wired and 802.11e values)? If so, if a packet that is tagged background or best effort does that mean in my configuration, packet aggregation will still occur? :

:

802.11n Status:
    A-MPDU Tx:
        Priority 0............................... Enabled
        Priority 1............................... Enabled
        Priority 2............................... Enabled
        Priority 3............................... Enabled
        Priority 4............................... Enabled
        Priority 5............................... Enabled
        Priority 6............................... Disabled
        Priority 7............................... Disabled
        Aggregation scheduler.................... Enabled
        Frame Burst.............................. Automatic
            Realtime Timeout..................... 10
    A-MSDU Tx:
        Priority 0............................... Enabled
        Priority 1............................... Enabled
        Priority 2............................... Enabled
        Priority 3............................... Enabled
        Priority 4............................... Enabled
        Priority 5............................... Enabled
        Priority 6............................... Disabled
        Priority 7............................... Disabled
    Rifs Rx ..................................... Enabled
 

Any insight will be greatly appreciated.

[George Stefanick]

You're going to make me go research this aren't you .. LOL

[IT Services]

Yeah but of course! Your too good at it! lol

[Viten Patel]

yes this means aggregation can happen if the STA gains the txop and chooses to send aggregated frames.

[IT Services]

Awesome. We are looking to resolve an issue with our Spectralink 8440 VoWLAN handsets. The issue really seems to be similar when we first started rolling out the phones. I have followed the Spectralink VIEW documentation but have only disabled aggregation on Priority 6 and 7 frames. It recommends disabling A-MSDU on all priorities. It looks like packets coming from the wired side are Background or Best effort packets.

If I were to disable MSDU aggregation on all priorities would this significantly impact our data WLANs that support 802.11n?

Also. This issue didn't become apparent until after we configured QoS on the wired network.

Thoughts?

[Viten Patel]

am guessing spectralink would send the data at priority 6 anyways and i doubt for voip traffic the STA will send aggregated frames...do you take a over the air sniff and confirm that.

[IT Services]

Yes I do have some OTA captures and it looks like any traffic returning to the Spectralink handset has MSDU values in the frame. Is this the correct assumption. See image:

[IT Services]

Anything more on this? I am curious if we follow the Cisco\Spectralink VIEW document by disabling A-MSDU on all priorities would this have any noticeable real-life impact on our other 802.11n clients?

In what scenario does A-MSDU come to being used? We are looking to keep A-MPDU at default (enabled for 0,4,5) and disabling all A-MSDU. Will we notice a major decrease in non-HT 802.11n performance?

[Rasika Nayanajith]

Yes,these priority value refer to 802.11e UP values (ie 1,2 - BK, 0,3-BE, 4,5-VI & 6,7-VO). You can enable/disable A-MSDU or A-MPDU for given priority. Refer this link for more detail

http://mrncciew.com/2013/04/11/a-mpdu-a-msdu/

HTH

Rasika

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