Hi Guy, Very informative about the radiotap header. It helps a lot:)
BTW, should adding radiotap header to a 802.11 packet be an option which can be selected by the user? If yes, which is by default? with radiotap or without it? In fact, I want to know how Linux implements this? I tend to keep the alike manner as other systems. Cheers, Yang On Thu, Apr 7, 2016 at 9:37 AM, Guy Harris <[email protected]> wrote: > On Apr 6, 2016, at 5:41 PM, Yang Luo <[email protected]> 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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