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Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO)
From: Yang Luo <hsluoyb () gmail com>
Date: Sun, 10 Apr 2016 14:17:21 +0800
Hi Guy, On Sun, Apr 10, 2016 at 10:22 AM, Guy Harris <guy () alum mit edu> wrote:
On Apr 9, 2016, at 7:15 PM, Yang Luo <hsluoyb () gmail com> wrote:And there's also a truncation from usDataRateValue (16 bits) to Radiotap"Rate" field (8 bits). I hope a direct assignment is OK:*((UCHAR*)Dot11RadiotapHeader + cur) = (UCHAR) usDataRateValue;For pre-11n PHYs (the fastest of which are 11a and 11g), the maximum data rate is < 255*.5 ~= 127 Mb/s, so it fits. For 11n and later PHYs, the data rate is calculated from values such as the MCS index; if the drivers aren't supplying that information (because they can't - Microsoft haven't updated the "Native Wi-Fi" radio metadata to handle 11n or 11ac), the drivers *might* be providing data rate values > 127 Mb/s, but there's not much we can do about that.
OK. Then if data rate values > 127 Mb/s, I will make it = 127 Mb/s at least instead of some strange overflowed values when truncated as the following code. I think this is currently the best solution for this. ------------------------------------------------------------------------------------------------ // [Radiotap] "Rate" field. // Looking up the ucDataRate field's value in the data rate mapping table. // If not found, return 0. USHORT usDataRateValue = NPF_LookUpDataRateMappingTable(Open, pwInfo->ucDataRate); pRadiotapHeader->it_present |= BIT(IEEE80211_RADIOTAP_RATE); if (usDataRateValue > 255) { usDataRateValue = 255; } *((UCHAR*)Dot11RadiotapHeader + cur) = (UCHAR) usDataRateValue; cur += sizeof(UCHAR) / sizeof(UCHAR); ------------------------------------------------------------------------------------------------ Cheers, Yang
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Current thread:
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Guy Harris (Apr 06)
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Yang Luo (Apr 06)
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Yang Luo (Apr 08)
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Guy Harris (Apr 09)
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Yang Luo (Apr 09)
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Guy Harris (Apr 09)
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Yang Luo (Apr 09)
- Re: [tcpdump-workers] What's the difference between NdisMediumBare80211 (DLT_IEEE802_11) and NdisMediumRadio80211 (DLT_IEEE802_11_RADIO) Guy Harris (Apr 09)