net80211 and PPI header

Sam Leffler sam at
Sat Feb 20 21:51:28 UTC 2010

Alexander Egorenkov wrote:
>> What exactly do you need? We should be able to extend radiotap.
> 1. Not only one RSSI but for every antenna (also in dBm)
> 2. HT greenfield/HT mixed indicator
> 4. Number of spatial streams (STBC)
> 3. A-MPDU support (MPDU density, A-MPDU reassembly)
> The most important one is A-MPDU support, i think.
> Wireshark supports PPI header and can handle A-MPDUs very nicely.
> That's it for now :-)

I discussed integrating PPI w/ radiotap back when I did the existing 11n 
support but never got anywhere (>3 years ago?).  The PPI stuff was done 
under contract to Intel and the folks involved never contacted anyone 
about doing it within radiotap instead.  It looked entirely possible to 
leverage the PPI decoder in wireshark to handle AMPDU reassembly from 
the radiotap decoder but I never got to it.

As to the other state Greenfield was nonexistent (and unclear if it'd 
make it out of draft status) when I did stuff or I'd have reserved a bit 
for it.  The # of streams can be implied from the MCS unless I 
misunderstand.  I do want the per-antenna/chain state (rssi, nf, evm) 
but was looking for things to stabilize before adding to radiotap--each 
device/driver exports different data and I wanted something that was 
enough of a superset to handle the most devices.  Adopting PPI data 
structures would be reasonable.

I would prefer to not emit PPI but instead augment radiotap.  We've 
standardized on radiotap for 802.11 and all the drivers now use it (or 
should use it).  I'll leave it to others to deal w/ the politics of the 
radiotap noobs; the technical details of doing this are straightforward.


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