View on GitHub


Introduction | defined fields | suggested fields | rejected fields


Bit Number
u32 flags, u16 freq, u8 channel, u8 maxpower
Required Alignment
none, MHz, 802.11 channel number, unknown

Extended channel information. The flags part of the field contains various flags:

flag definition
0x00000010 Channel Type Turbo
0x00000020 Channel Type Complementary Code Keying (CCK) Modulation
0x00000040 Channel Type Orthogonal Frequency-Division Multiplexing (OFDM)
0x00000080 Channel Type 2 GHz spectrum
0x00000100 Channel Type 5 GHz spectrum
0x00000200 Channel Type Passive
0x00000400 Channel Type Dynamic CCK-OFDM Channel
0x00000800 Channel Type Gaussian Frequency Shift Keying (GFSK) Modulation
0x00001000 Channel Type GSM
0x00002000 Channel Type Status Turbo
0x00004000 Channel Type Half Rate
0x00008000 Channel Type Quarter Rate
0x00010000 Channel Type HT/20
0x00020000 Channel Type HT/40+
0x00040000 Channel Type HT/40-


This field is parsed by wireshark, but only partially (it ignores maxpower). Origin of the field is unknown. Used by FreeBSD and OS X.

Channel numbers are problematic – using the channel’s center frequency would be much better.

The flags define some things that can be inferred (2 vs. 5 GHz).

Things like the “Channel Type Passive” don’t make sense per packet. As used, this field conflates channel properties (which need not be stored per packet but are more or less fixed) with packet properties (like the modulation).