On Apr 6, 2016, at 5:41 PM, Yang Luo wrote:
> I wonder why this mail went to my spam.. I don't know anything about radiotap
> header so I'm afraid i'm not supplying it.
It's a way to provide "radio metadata" for packets; see
http://www.radiotap.org
for a description of it.
If you were to implement that in the future, you'd get the "Media-Specific OOB
Data for Received 802.11 Packets":
https://msdn.microsoft.com/en-us/library/windows/hardware/ff559169(v=vs.85).aspx
in a DOT11_EXTSTA_RECV_CONTEXT structure:
https://msdn.microsoft.com/en-us/library/windows/hardware/ff548626(v=vs.85).aspx
when you receive a packet. Then you'd provide a link-layer header type of
DLT_IEEE802_11_RADIO, and synthesize a radiotap header. When you open the
device, you'd have to fetch the device's data rate mapping table with the
OID_DOT11_DATA_RATE_MAPPING_TABLE OID:
https://msdn.microsoft.com/en-us/library/windows/hardware/ff569139(v=vs.85).aspx
https://msdn.microsoft.com/en-us/library/windows/hardware/ff547679(v=vs.85).aspx
and associate that with the private data for the pcap_t.
Then, for each received packet:
if DOT11_RECV_FLAG_RAW_PACKET_TIMESTAMP is set in uReceiveFlags, provide a
radiotap TSFT field with the value from the ullTimestamp field of the structure;
provide a radiotap Flags field with 0x10 set if the frame includes the FCS
(you'll probably have to experiment a bit to see whether you get the FCS or not
- the answer might differ for data and management frames, based on Network
Monitor's behavior) and with 0x40 set if DOT11_RECV_FLAG_RAW_PACKET_FCS_FAILURE
is set in uReceiveFlags;
provide a radiotap Rate field whose value is the result of looking up the
ucDataRate field's value in the data rate mapping table and returning the
usDataRateValue value from that table - if it's not found, don't provide the
Rate field;
provide a radiotap Channel field where the frequency value is the
uChCenterFrequency field of the structure and the flags are derived from the
uChCenterFrequency and uPhyId fields of the structure - assuming that the
uPhyId value is one of the ones from
https://msdn.microsoft.com/en-us/library/windows/hardware/ff548741(v=vs.85).aspx
then the mapping would be:
dot11_phy_type_fhss - set 0x0800 in the flags (11 legacy FHSS);
dot11_phy_type_ofdm - set 0x0040 in the flags (11a);
dot11_phy_type_hrdsss - set 0x0020 in the flags (11b);
dot11_phy_type_erp - set 0x0040 in the flags (11g, unknown whether it's
pure or not);
and, unless it's dot11_phy_type_irbaseband, set 0x0100 if the frequency is
in the 5 GHz range or set 0x0080 if it's in the 2.4 GHz range;
provide a radiotap Antenna signal field whose value is the value of the
lRSSI field in the structure;
if the phy is dot11_phy_type_ht, provide a radiotap MCS field where the
known field is 0 and the other fields are also zeroed out (i.e., it's 11n, but
we don't know anything else about it);
if the phy is dot11_phy_type_vht, provide a radiotap VHT field where the
known field is 0 and the other fields are also zeroed out (i.e., it's 11ac, but
we don't know anything else about it).
> And I have confirmed that my captured packets are parsed well using
> NdisMediumBare80211. In Wireshark it shows "IEEE 802.11 Data".
That means that you're just supplying packets that begin with an 802.11 header,
with no form of radio information preceding it, so...
> So I think I will just use this value.
...that is exactly what you should be doing.
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