Wireshark-bugs: [Wireshark-bugs] [Bug 11277] Problem in decoding Wifi Traffic with MPDU aggregat
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From: bugzilla-daemon@xxxxxxxxxxxxx
Date: Tue, 16 Jun 2015 01:48:03 +0000

Comment # 2 on bug 11277 from 
OK, so I assume all the frames in that capture were transmitted over the air in
a single link-layer packet, but were presented to the host as multiple
individual packets.

The radiotap page for the A-MPDU status field:

    http://www.radiotap.org/defined-fields/A-MPDU%20status

doesn't indicate how the 802.11 frame after the radiotap header is to be
interpreted.

At least as I read section 3.2.3 "A-MPDU Mechanism" in the document to which
Evan provided a link, the link-layer packet has a PHY header followed by a
sequence of items, each item containing, in order:

    the delimiter (reserved, MPDU length, CRC, unique pattern);
    a raw 802.11 MAC-layer PDU, complete with MAC header, payload (MSDU), and
FCS;
    padding.

I would expect an adapter that presents that to the host as multiple individual
packets to just present each of the raw 802.11 MAC-layer PDUs, without the
delimiter or padding.  If that's what was intended for A-MPDU aggregation in
radiotap captures, whatever produced that capture file is buggy; if that isn't
what was intended for radiotap captures, the radiotap documentation needs to be
clearer on what's provided.

I'll have to see if this was discussed on the radiotap mailing list and, if
not, ask for clarification.

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