[This is with madwifi-0.9.4 release version.].
I want a node to be able to see all incorrectly received packets with
a radiotap header attached. Here is my setup: Node A and B are sending
packets to each other. Node C is in monitor mode and is sniffing. I am
particularly interested in incorrectly received packets at C (mostly
likely due to collision of pkts from A and B).
I set up the node C in monitor mode, enable the radiotap header, and
ask it to pass up erroneous packets. (nodes A and B are in adhoc-demo
mode). The ACKs are disabled, and Txop is enabled on all nodes (hacked
ahdemo mode to support WMM).
After getting the pcap trace and loading it in wireshark, I see that
almost all malformed packets are kind of empty -- there is only a
radiotap header attached to them. And the frame size is 26 (where 26
is the radiotap header size). Also the radiotap header does not say
that the FCS failed.
However there are very few (less than 5 out of thousands) where I get
the desired behaviour: The bits are received incorrectly, radiotap
shows FCS failed and the data contents are still there.
But I am not sure what's happening to the other 995+ frames. I am
wondering whether it is because for those frames, even the preamble is
not getting through and hence the HAL reports an empty packet up ?.
But it is surprising that this is happening almost always.
I can share the pcap trace, if that helps. I would be happy to share
any other information if it helps debugging this problem. Thanks a lot
for your time.