887a63246c
This field may be used for received frames only. Differential Revision: https://reviews.freebsd.org/D3826 Differential Revision: https://reviews.freebsd.org/D3827
301 lines
11 KiB
Groff
301 lines
11 KiB
Groff
.\"
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.\" Copyright (c) 2004 Bruce M. Simpson <bms@spc.org>,
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.\" Darron Broad <darron@kewl.org>,
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.\" David Young <dyoung@pobox.com>.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 4, 2009
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.Dt IEEE80211_RADIOTAP 9
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.Os
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.Sh NAME
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.Nm ieee80211_radiotap
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.Nd 802.11 device packet capture support
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.Sh SYNOPSIS
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.In net80211/ieee80211_var.h
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.\"
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.Pp
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.Ft void
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.Fo ieee80211_radiotap_attach
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.Fa "struct ieee80211com *"
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.Fa "struct ieee80211_radiotap_header *th"
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.Fa "int tlen"
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.Fa "uint32_t tx_radiotap"
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.Fa "struct ieee80211_radiotap_header *rh"
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.Fa "int rlen"
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.Fa "uint32_t rx_radiotap"
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.Fc
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.\"
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.Ft int
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.Fn ieee80211_radiotap_active_vap "struct ieee80211vap *"
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.\"
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.Ft int
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.Fn ieee80211_radiotap_active "struct ieee80211com *"
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.\"
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.Ft void
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.Fn ieee80211_radiotap_tx "struct ieee80211vap *" "struct mbuf *"
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.Sh DESCRIPTION
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The
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.Nm net80211
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layer used by 802.11 drivers includes support for a device-independent
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packet capture format called
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.Nm radiotap
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that is understood by tools such as
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.Xr tcpdump 1 .
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This facility is designed for capturing 802.11 traffic,
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including information that is not part of the normal 802.11 frame structure.
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.Pp
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Radiotap was designed to balance the desire for a hardware-independent,
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extensible capture format against the need to
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conserve CPU and memory bandwidth on embedded systems.
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These considerations led to a format consisting of
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a standard preamble followed by an extensible bitmap indicating the
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presence of optional capture fields.
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A
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.Nm net80211
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device driver supporting
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.Vt radiotap
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defines two packed structures that it shares with
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.Nm net80211 .
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These structures embed an instance of a
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.Vt ieee80211_radiotap_header
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structure at the beginning,
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with subsequent fields in the appropriate order,
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and macros to set the bits of the
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.Va it_present
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bitmap to indicate which fields exist and are filled in by the driver.
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This information is then supplied through the
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.Fn ieee80211_radiotap_attach
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call after a successful
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.Fn ieee80211_ifattach
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request.
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.Pp
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With radiotap setup, drivers just need to fill in per-packet
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capture state for frames sent/received and dispatch capture state
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in the transmit path (since control is not returned to the
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.Nm net80211
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layer before the packet is handed to the device).
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To minimize overhead this work should be done only when one
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or more processes are actively capturing data;
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this is checked with one of
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.Fn ieee80211_radiotap_active_vap
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and
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.Fn ieee80211_radiotap_active .
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In the transmit path capture work looks like this:
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.Bd -literal -offset indent
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if (ieee80211_radiotap_active_vap(vap)) {
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... /* record transmit state */
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ieee80211_radiotap_tx(vap, m); /* capture transmit event */
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}
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.Ed
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.Pp
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While in the receive path capture is handled in
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.Nm net80211
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but state must be captured before dispatching a frame:
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.Bd -literal -offset indent
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if (ieee80211_radiotap_active(ic)) {
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... /* record receive state */
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}
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\&...
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ieee80211_input(...); /* packet capture handled in net80211 */
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.Ed
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.Pp
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.\"
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The following fields are defined for
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.Vt radiotap ,
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in the order in which they should appear in the buffer supplied
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to
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.Nm net80211 .
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.Bl -tag -width indent
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.It Dv IEEE80211_RADIOTAP_TSFT
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This field contains the unsigned 64-bit value, in microseconds,
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of the MAC's 802.11 Time Synchronization Function (TSF).
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In theory, for each received frame, this value is recorded
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when the first bit of the MPDU arrived at the MAC.
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In practice, hardware snapshots the TSF otherwise and one cannot assume
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this data is accurate without driver adjustment.
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.It Dv IEEE80211_RADIOTAP_FLAGS
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This field contains a single unsigned 8-bit value, containing one or
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more of these bit flags:
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.Bl -tag -width indent
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.It Dv IEEE80211_RADIOTAP_F_CFP
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Frame was sent/received during the Contention Free Period (CFP).
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.It Dv IEEE80211_RADIOTAP_F_SHORTPRE
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Frame was sent/received with short preamble.
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.It Dv IEEE80211_RADIOTAP_F_WEP
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Frame was encrypted.
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.It Dv IEEE80211_RADIOTAP_F_FRAG
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Frame was an 802.11 fragment.
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.It Dv IEEE80211_RADIOTAP_F_FCS
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Frame contents includes the FCS.
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.It Dv IEEE80211_RADIOTAP_F_DATAPAD
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Frame contents potentially has padding between the 802.11 header and the
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data payload to align the payload to a 32-bit boundary.
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.It Dv IEEE80211_RADIOTAP_F_BADFCS
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Frame was received with an invalid FCS.
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.It Dv IEEE80211_RADIOTAP_F_SHORTGI
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Frame was sent/received with Short Guard Interval.
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.El
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.It Dv IEEE80211_RADIOTAP_RATE
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This field contains a single unsigned 8-bit value that is the data rate.
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Legacy rates are in units of 500Kbps.
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MCS rates (used on 802.11n/HT channels) have the high bit set and
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the MCS in the low 7 bits.
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.It Dv IEEE80211_RADIOTAP_CHANNEL
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This field contains two unsigned 16-bit values.
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The first value is the center frequency for the channel
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the frame was sent/received on.
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The second value is a bitmap containing flags that specify channel properties.
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.Pp
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This field is deprecated in favor of
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.Dv IEEE80211_RADIOTAP_XCHANNEL
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but may be used to save space in the capture file for legacy devices.
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.\".It Dv IEEE80211_RADIOTAP_FHSS
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.\"This field contains two 8-bit values.
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.\"This field should be present only for frequency-hopping radios.
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.\"The first byte is the hop set.
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.\"The second byte is the pattern in use.
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.It Dv IEEE80211_RADIOTAP_DBM_ANTSIGNAL
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This field contains a single signed 8-bit value that indicates the
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RF signal power at the antenna, in decibels difference from 1mW.
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.It Dv IEEE80211_RADIOTAP_DBM_ANTNOISE
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This field contains a single signed 8-bit value that indicates the
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RF noise power at the antenna, in decibels difference from 1mW.
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.\".It Dv IEEE80211_RADIOTAP_LOCK_QUALITY
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.\"This field contains a single unsigned 16-bit value, indicating the
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.\"quality of the Barker Code lock.
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.\"No unit is specified for this field.
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.\"There does not appear to be a standard way of measuring this at this time;
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.\"this quantity is often referred to as
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.\".Dq "Signal Quality"
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.\"in some datasheets.
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.\".It Dv IEEE80211_RADIOTAP_TX_ATTENUATION
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.\"This field contains a single unsigned 16-bit value, expressing transmit
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.\"power as unitless distance from maximum power set at factory calibration.
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.\"0 indicates maximum transmit power.
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.\"Monotonically nondecreasing with lower power levels.
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.\".It Dv IEEE80211_RADIOTAP_DB_TX_ATTENUATION
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.\"This field contains a single unsigned 16-bit value, expressing transmit
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.\"power as decibel distance from maximum power set at factory calibration.
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.\"0 indicates maximum transmit power.
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.\"Monotonically nondecreasing with lower power levels.
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.It Dv IEEE80211_RADIOTAP_DBM_TX_POWER
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Transmit power expressed as decibels from a 1mW reference.
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This field is a single signed 8-bit value.
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This is the absolute power level measured at the antenna port.
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.It Dv IEEE80211_RADIOTAP_ANTENNA
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This field contains a single unsigned 8-bit value that specifies
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which antenna was used to transmit or receive the frame.
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Antenna numbering is device-specific but typically the primary antenna has
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the lowest number.
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On transmit a value of zero may be seen which typically means
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antenna selection is left to the device.
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.It Dv IEEE80211_RADIOTAP_DB_ANTSIGNAL
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This field contains a single unsigned 8-bit value that indicates the
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RF signal power at the antenna, in decibels difference from an
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arbitrary, fixed reference.
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.It Dv IEEE80211_RADIOTAP_DB_ANTNOISE
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This field contains a single unsigned 8-bit value that indicates the
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RF noise power at the antenna, in decibels difference from an
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arbitrary, fixed reference.
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.It Dv IEEE80211_RADIOTAP_XCHANNEL
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This field contains four values: a 32-bit unsigned bitmap of
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flags that describe the channel attributes, a 16-bit unsigned
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frequency in MHz (typically the channel center), an 8-bit
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unsigned IEEE channel number, and a signed 8-bit value that
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holds the maximum regulatory transmit power cap in .5 dBm
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(8 bytes total).
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Channel flags are defined in:
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.In net80211/_ieee80211.h
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(only a subset are found in
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.In net80211/ieee80211_radiotap.h ).
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This property supersedes
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.Dv IEEE80211_RADIOTAP_CHANNEL
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and is the only way to completely express all
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channel attributes and the
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mapping between channel frequency and IEEE channel number.
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.El
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.Sh EXAMPLES
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Radiotap receive definitions for the Intersil Prism driver:
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.Bd -literal -offset indent
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#define WI_RX_RADIOTAP_PRESENT \\
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((1 << IEEE80211_RADIOTAP_TSFT) \\
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(1 << IEEE80211_RADIOTAP_FLAGS) | \\
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(1 << IEEE80211_RADIOTAP_RATE) | \\
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(1 << IEEE80211_RADIOTAP_CHANNEL) | \\
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(1 << IEEE80211_RADIOTAP_DB_ANTSIGNAL) | \\
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(1 << IEEE80211_RADIOTAP_DB_ANTNOISE))
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struct wi_rx_radiotap_header {
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struct ieee80211_radiotap_header wr_ihdr;
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uint64_t wr_tsf;
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uint8_t wr_flags;
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uint8_t wr_rate;
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uint16_t wr_chan_freq;
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uint16_t wr_chan_flags;
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uint8_t wr_antsignal;
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uint8_t wr_antnoise;
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} __packed;
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.Ed
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.Pp
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and transmit definitions for the Atheros driver:
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.Bd -literal -offset indent
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#define ATH_TX_RADIOTAP_PRESENT ( \\
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(1 << IEEE80211_RADIOTAP_FLAGS) | \\
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(1 << IEEE80211_RADIOTAP_RATE) | \\
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(1 << IEEE80211_RADIOTAP_DBM_TX_POWER) | \\
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(1 << IEEE80211_RADIOTAP_ANTENNA) | \\
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(1 << IEEE80211_RADIOTAP_XCHANNEL) | \\
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0)
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struct ath_tx_radiotap_header {
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struct ieee80211_radiotap_header wt_ihdr;
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uint8_t wt_flags;
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uint8_t wt_rate;
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uint8_t wt_txpower;
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uint8_t wt_antenna;
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uint32_t wt_chan_flags;
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uint16_t wt_chan_freq;
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uint8_t wt_chan_ieee;
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int8_t wt_chan_maxpow;
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} __packed;
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.Ed
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.Sh SEE ALSO
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.Xr tcpdump 1 ,
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.Xr bpf 4 ,
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.Xr ieee80211 9
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.Sh HISTORY
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The
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.Nm
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definitions first appeared in
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.Nx 1.5 .
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.\"
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.Sh AUTHORS
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.An -nosplit
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The original version of this manual page was written by
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.An Bruce M. Simpson Aq Mt bms@FreeBSD.org
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and
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.An Darron Broad Aq Mt darron@kewl.org .
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