A-MSDU reception not working?

Denton Gentry denton.gentry at gmail.com
Mon Jun 30 13:15:14 PDT 2014

In iperf tests using a MacBook STA bridging through an ath10k AP to an
Ethernet server, I'm noticing very selective packet loss. The second
and subsequent frames in an A-MSDU packet appear to be dropped.

The AP sets the A-MSDU size to 3839 bytes, and the MacBook frequently
sends A-MSDU packets containing two TCP frames. So far as I can tell,
the first TCP frame from an A-MSDU aggregate is delivered and the
second is consistently lost. The MacBook generally retransmits the
lost frame as a singleton with no aggregation, and the retransmitted
frame makes it through.

This became more noticeable after the reordering fixes in

I see this A-MSDU packet loss behavior both with and without the
reordering fixes, the first packet in an A-MSDU is delivered while the
second is dropped. However, *without* the reordering fixes (and
therefore with packets delivered out of order) the MacBook sends
relatively few A-MSDU frames. *With* the reordering fixes, so all
packets are delivered in order, the MacBook keeps sending A-MSDU and
therefore has to deal with more packet loss. I suspect it is an
interaction with the MacOS TCP congestion window which I'm likely
never going to fully understand, its stuck in a region of the
congestion window where the Wifi driver keeps choosing to using

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