IEEE80211(9) FreeBSD Kernel Developer's Manual IEEE80211(9)
NAME
IEEE80211 - 802.11 network layer
SYNOPSIS
#include <net80211/ieee80211_var.h>
void
ieee80211_ifattach(struct ieee80211com *ic);
void
ieee80211_ifdetach(struct ieee80211com *ic);
int
ieee80211_mhz2ieee(u_int freq, u_int flags);
int
ieee80211_chan2ieee(struct ieee80211com *ic,
const struct ieee80211_channel *c);
u_int
ieee80211_ieee2mhz(u_int chan, u_int flags);
int
ieee80211_media_change(struct ifnet *ifp);
void
ieee80211_media_status(struct ifnet *ifp, struct ifmediareq *imr);
int
ieee80211_setmode(struct ieee80211com *ic, enum ieee80211_phymode mode);
enum ieee80211_phymode
ieee80211_chan2mode(const struct ieee80211_channel *chan);
int
ieee80211_rate2media(struct ieee80211com *ic, int rate,
enum ieee80211_phymode mode);
int
ieee80211_media2rate(int mword);
DESCRIPTION
IEEE 802.11 device drivers are written to use the infrastructure provided
by the IEEE80211 software layer. This software provides a support
framework for drivers that includes ifnet cloning, state management, and
a user management API by which applications interact with 802.11 devices.
Most drivers depend on the IEEE80211 layer for protocol services but
devices that off-load functionality may bypass the layer to connect
directly to the device (e.g. the ndis(4) emulation support does this).
A IEEE80211 device driver implements a virtual radio API that is exported
to users through network interfaces (aka vaps) that are cloned from the
underlying device. These interfaces have an operating mode (station,
adhoc, hostap, wds, monitor, etc.) that is fixed for the lifetime of the
interface. Devices that can support multiple concurrent interfaces allow
multiple vaps to be cloned. This enables construction of interesting
applications such as an AP vap and one or more WDS vaps or multiple AP
vaps, each with a different security model. The IEEE80211 layer
virtualizes most 802.11 state and coordinates vap state changes including
scheduling multiple vaps. State that is not virtualized includes the
current channel and WME/WMM parameters. Protocol processing is typically
handled entirely in the IEEE80211 layer with drivers responsible purely
for moving data between the host and device. Similarly, IEEE80211
handles most ioctl(2) requests without entering the driver; instead
drivers are notified of state changes that require their involvement.
The virtual radio interface defined by the IEEE80211 layer means that
drivers must be structured to follow specific rules. Drivers that
support only a single interface at any time must still follow these
rules.
Most of these functions require that attachment to the stack is performed
before calling.
The ieee80211_ifattach() function attaches the wireless network interface
ic to the 802.11 network stack layer. This function must be called
before using any of the IEEE80211 functions which need to store driver
state across invocations.
The ieee80211_ifdetach() function frees any IEEE80211 structures
associated with the driver, and performs Ethernet and BPF detachment on
behalf of the caller.
The ieee80211_mhz2ieee() utility function converts the frequency freq
(specified in MHz) to an IEEE 802.11 channel number. The flags argument
is a hint which specifies whether the frequency is in the 2GHz ISM band
(IEEE80211_CHAN_2GHZ) or the 5GHz band (IEEE80211_CHAN_5GHZ); appropriate
clipping of the result is then performed.
The ieee80211_chan2ieee() function converts the channel specified in *c
to an IEEE channel number for the driver ic. If the conversion would be
invalid, an error message is printed to the system console. This
function REQUIRES that the driver is hooked up to the IEEE80211
subsystem.
The ieee80211_ieee2mhz() utility function converts the IEEE channel
number chan to a frequency (in MHz). The flags argument is a hint which
specifies whether the frequency is in the 2GHz ISM band
(IEEE80211_CHAN_2GHZ) or the 5GHz band (IEEE80211_CHAN_5GHZ); appropriate
clipping of the result is then performed.
The ieee80211_media_status() and ieee80211_media_change() functions are
device-independent handlers for ifmedia commands and are not intended to
be called directly.
The ieee80211_setmode() function is called from within the 802.11 stack
to change the mode of the driver's PHY; it is not intended to be called
directly.
The ieee80211_chan2mode() function returns the PHY mode required for use
with the channel chan. This is typically used when selecting a rate set,
to be advertised in beacons, for example.
The ieee80211_rate2media() function converts the bit rate rate (measured
in units of 0.5Mbps) to an ifmedia sub-type, for the device ic running in
PHY mode mode. The ieee80211_media2rate() performs the reverse of this
conversion, returning the bit rate (in 0.5Mbps units) corresponding to an
ifmedia sub-type.
DATA STRUCTURES
The virtual radio architecture splits state between a single per-device
ieee80211com structure and one or more ieee80211vap structures. Drivers
are expected to setup various shared state in these structures at device
attach and during vap creation but otherwise should treat them as read-
only. The ieee80211com structure is allocated by the IEEE80211 layer as
adjunct data to a device's ifnet; it is accessed through the if_l2com
structure member. The ieee80211vap structure is allocated by the driver
in the "vap create" method and should be extended with any driver-private
state. This technique of giving the driver control to allocate data
structures is used for other IEEE80211 data structures and should be
exploited to maintain driver-private state together with public IEEE80211
state.
The other main data structures are the station, or node, table that
tracks peers in the local BSS, and the channel table that defines the
current set of available radio channels. Both tables are bound to the
ieee80211com structure and shared by all vaps. Long-lasting references
to a node are counted to guard against premature reclamation. In
particular every packet sent/received holds a node reference (either
explicitly for transmit or implicitly on receive).
The ieee80211com and ieee80211vap structures also hold a collection of
method pointers that drivers fill-in and/or override to take control of
certain operations. These methods are the primary way drivers are bound
to the IEEE80211 layer and are described below.
DRIVER ATTACH/DETACH
Drivers attach to the IEEE80211 layer with the ieee80211_ifattach()
function. The driver is expected to allocate and setup any device-
private data structures before passing control. The ieee80211com
structure must be pre-initialized with state required to setup the
IEEE80211 layer:
ic_ifp Backpointer to the physical device's ifnet.
ic_caps Device/driver capabilities; see below for a complete
description.
ic_channels Table of channels the device is capable of operating on.
This is initially provided by the driver but may be changed
through calls that change the regulatory state.
ic_nchan Number of entries in ic_channels.
On return from ieee80211_ifattach() the driver is expected to override
default callback functions in the ieee80211com structure to register it's
private routines. Methods marked with a "*" must be provided by the
driver.
ic_vap_create*
Create a vap instance of the specified type (operating
mode). Any fixed BSSID and/or MAC address is provided.
Drivers that support multi-bssid operation may honor the
requested BSSID or assign their own.
ic_vap_delete*
Destroy a vap instance created with ic_vap_create.
ic_getradiocaps
Return the list of calibrated channels for the radio. The
default method returns the current list of channels (space
permitting).
ic_setregdomain
Process a request to change regulatory state. The routine
may reject a request or constrain changes (e.g. reduce
transmit power caps). The default method accepts all
proposed changes.
ic_send_mgmt
Send an 802.11 management frame. The default method
fabricates the frame using IEEE80211 state and passes it to
the driver through the ic_raw_xmit method.
ic_raw_xmit Transmit a raw 802.11 frame. The default method drops the
frame and generates a message on the console.
ic_updateslot
Update hardware state after an 802.11 IFS slot time change.
There is no default method; the pointer may be NULL in which
case it will not be used.
ic_update_mcast
Update hardware for a change in the multicast packet filter.
The default method prints a console message.
ic_update_promisc
Update hardware for a change in the promiscuous mode
setting. The default method prints a console message.
ic_newassoc Update driver/device state for association to a new AP (in
station mode) or when a new station associates (e.g. in AP
mode). There is no default method; the pointer may be NULL
in which case it will not be used.
ic_node_alloc
Allocate and initialize a ieee80211_node structure. This
method cannot sleep. The default method allocates zero'd
memory using malloc(9). Drivers should override this method
to allocate extended storage for their own needs. Memory
allocated by the driver must be tagged with M_80211_NODE to
balance the memory allocation statistics.
ic_node_free
Reclaim storage of a node allocated by ic_node_alloc.
Drivers are expected to interpose their own method to
cleanup private state but must call through this method to
allow IEEE80211 to reclaim it's private state.
ic_node_cleanup
Cleanup state in a ieee80211_node created by ic_node_alloc.
This operation is distinguished from ic_node_free in that it
may be called long before the node is actually reclaimed to
cleanup adjunct state. This can happen, for example, when a
node must not be reclaimed due to references held by packets
in the transmit queue. Drivers typically interpose
ic_node_cleanup instead of ic_node_free.
ic_node_age Age, and potentially reclaim, resources associated with a
node. The default method ages frames on the power-save
queue (in AP mode) and pending frames in the receive reorder
queues (for stations using A-MPDU).
ic_node_drain
Reclaim all optional resources associated with a node. This
call is used to free up resources when they are in short
supply.
ic_node_getrssi
Return the Receive Signal Strength Indication (RSSI) in .5
dBm units for the specified node. This interface returns a
subset of the information returned by ic_node_getsignal.
The default method calculates a filtered average over the
last ten samples passed in to ieee80211_input(9) or
ieee80211_input_all(9).
ic_node_getsignal
Return the RSSI and noise floor (in .5 dBm units) for a
station. The default method calculates RSSI as described
above; the noise floor returned is the last value supplied
to ieee80211_input(9) or ieee80211_input_all(9).
ic_node_getmimoinfo
Return MIMO radio state for a station in support of the
IEEE80211_IOC_STA_INFO ioctl request. The default method
returns nothing.
ic_scan_start*
Prepare driver/hardware state for scanning. This callback
is done in a sleepable context.
ic_scan_end*
Restore driver/hardware state after scanning completes.
This callback is done in a sleepable context.
ic_set_channel*
Set the current radio channel using ic_curchan. This
callback is done in a sleepable context.
ic_scan_curchan
Start scanning on a channel. This method is called
immediately after each channel change and must initiate the
work to scan a channel and schedule a timer to advance to
the next channel in the scan list. This callback is done in
a sleepable context. The default method handles active scan
work (e.g. sending ProbeRequest frames), and schedules a
call to ieee80211_scan_next(9) according to the maximum
dwell time for the channel. Drivers that off-load scan work
to firmware typically use this method to trigger per-channel
scan activity.
ic_scan_mindwell
Handle reaching the minimum dwell time on a channel when
scanning. This event is triggered when one or more stations
have been found on a channel and the minimum dwell time has
been reached. This callback is done in a sleepable context.
The default method signals the scan machinery to advance to
the next channel as soon as possible. Drivers can use this
method to preempt further work (e.g. if scanning is handled
by firmware) or ignore the request to force maximum dwell
time on a channel.
ic_recv_action
Process a received Action frame. The default method points
to ieee80211_recv_action(9) which provides a mechanism for
setting up handlers for each Action frame class.
ic_send_action
Transmit an Action frame. The default method points to
ieee80211_send_action(9) which provides a mechanism for
setting up handlers for each Action frame class.
ic_ampdu_enable
Check if transmit A-MPDU should be enabled for the specified
station and AC. The default method checks a per-AC traffic
rate against a per-vap threshold to decide if A-MPDU should
be enabled. This method also rate-limits ADDBA requests so
that requests are not made too frequently when a receiver
has limited resources.
ic_addba_request
Request A-MPDU transmit aggregation. The default method
sets up local state and issues an ADDBA Request Action
frame. Drivers may interpose this method if they need to
setup private state for handling transmit A-MPDU.
ic_addb_response
Process a received ADDBA Response Action frame and setup
resources as needed for doing transmit A-MPDU.
ic_addb_stop
Shutdown an A-MPDU transmit stream for the specified station
and AC. The default method reclaims local state after
sending a DelBA Action frame.
ic_bar_response
Process a response to a transmitted BAR control frame.
ic_ampdu_rx_start
Prepare to receive A-MPDU data from the specified station
for the TID.
ic_ampdu_rx_stop
Terminate receipt of A-MPDU data from the specified station
for the TID.
Once the IEEE80211 layer is attached to a driver there are two more steps
typically done to complete the work:
1. Setup "radiotap support" for capturing raw 802.11 packets that pass
through the device. This is done with a call to
ieee80211_radiotap_attach(9).
2. Do any final device setup like enabling interrupts.
State is torn down and reclaimed with a call to ieee80211_ifdetach().
Note this call may result in multiple callbacks into the driver so it
should be done before any critical driver state is reclaimed. On return
from ieee80211_ifdetach() all associated vaps and ifnet structures are
reclaimed or inaccessible to user applications so it is safe to teardown
driver state without worry about being re-entered. The driver is
responsible for calling if_free(9) on the ifnet it allocated for the
physical device.
DRIVER CAPABILITIES
Driver/device capabilities are specified using several sets of flags in
the ieee80211com structure. General capabilities are specified by
ic_caps. Hardware cryptographic capabilities are specified by
ic_cryptocaps. 802.11n capabilities, if any, are specified by ic_htcaps.
The IEEE80211 layer propagates a subset of these capabilities to each vap
through the equivalent fields: iv_caps, iv_cryptocaps, and iv_htcaps.
The following general capabilities are defined:
IEEE80211_C_STA Device is capable of operating in station (aka
Infrastructure) mode.
IEEE80211_C_8023ENCAP Device requires 802.3-encapsulated frames be
passed for transmit. By default IEEE80211 will
encapsulate all outbound frames as 802.11 frames
(without a PLCP header).
IEEE80211_C_FF Device supports Atheros Fast-Frames.
IEEE80211_C_TURBOP Device supports Atheros Dynamic Turbo mode.
IEEE80211_C_IBSS Device is capable of operating in adhoc/IBSS mode.
IEEE80211_C_PMGT Device supports dynamic power-management (aka
power save) in station mode.
IEEE80211_C_HOSTAP Device is capable of operating as an Access Point
in Infrastructure mode.
IEEE80211_C_AHDEMO Device is capable of operating in Adhoc Demo mode.
In this mode the device is used purely to
send/receive raw 802.11 frames.
IEEE80211_C_SWRETRY Device supports software retry of transmitted
frames.
IEEE80211_C_TXPMGT Device support dynamic transmit power changes on
transmitted frames; also known as Transmit Power
Control (TPC).
IEEE80211_C_SHSLOT Device supports short slot time operation (for
802.11g).
IEEE80211_C_SHPREAMBLE
Device supports short preamble operation (for
802.11g).
IEEE80211_C_MONITOR Device is capable of operating in monitor mode.
IEEE80211_C_DFS Device supports radar detection and/or DFS. DFS
protocol support can be handled by IEEE80211 but
the device must be capable of detecting radar
events.
IEEE80211_C_MBSS Device is capable of operating in MeshBSS (MBSS)
mode (as defined by 802.11s Draft 3.0).
IEEE80211_C_WPA1 Device supports WPA1 operation.
IEEE80211_C_WPA2 Device supports WPA2/802.11i operation.
IEEE80211_C_BURST Device supports frame bursting.
IEEE80211_C_WME Device supports WME/WMM operation (at the moment
this is mostly support for sending and receiving
QoS frames with EDCF).
IEEE80211_C_WDS Device supports transmit/receive of 4-address
frames.
IEEE80211_C_BGSCAN Device supports background scanning.
IEEE80211_C_TXFRAG Device supports transmit of fragmented 802.11
frames.
IEEE80211_C_TDMA Device is capable of operating in TDMA mode.
The follow general crypto capabilities are defined. In general IEEE80211
will fall-back to software support when a device is not capable of
hardware acceleration of a cipher. This can be done on a per-key basis.
IEEE80211 can also handle software Michael calculation combined with
hardware AES acceleration.
IEEE80211_CRYPTO_WEP Device supports hardware WEP cipher.
IEEE80211_CRYPTO_TKIP Device supports hardware TKIP cipher.
IEEE80211_CRYPTO_AES_OCB
Device supports hardware AES-OCB cipher.
IEEE80211_CRYPTO_AES_CCM
Device supports hardware AES-CCM cipher.
IEEE80211_CRYPTO_TKIPMIC
Device supports hardware Michael for use with
TKIP.
IEEE80211_CRYPTO_CKIP Devices supports hardware CKIP cipher.
The follow general 802.11n capabilities are defined. The first
capabilities are defined exactly as they appear in the 802.11n
specification. Capabilities beginning with IEEE80211_HTC_AMPDU are used
solely by the IEEE80211 layer.
IEEE80211_HTCAP_CHWIDTH40
Device supports 20/40 channel width operation.
IEEE80211_HTCAP_SMPS_DYNAMIC
Device supports dynamic SM power save operation.
IEEE80211_HTCAP_SMPS_ENA
Device supports static SM power save operation.
IEEE80211_HTCAP_GREENFIELD
Device supports Greenfield preamble.
IEEE80211_HTCAP_SHORTGI20
Device supports Short Guard Interval on 20MHz
channels.
IEEE80211_HTCAP_SHORTGI40
Device supports Short Guard Interval on 40MHz
channels.
IEEE80211_HTCAP_TXSTBC
Device supports Space Time Block Convolution
(STBC) for transmit.
IEEE80211_HTCAP_RXSTBC_1STREAM
Device supports 1 spatial stream for STBC receive.
IEEE80211_HTCAP_RXSTBC_2STREAM
Device supports 1-2 spatial streams for STBC
receive.
IEEE80211_HTCAP_RXSTBC_3STREAM
Device supports 1-3 spatial streams for STBC
receive.
IEEE80211_HTCAP_MAXAMSDU_7935
Device supports A-MSDU frames up to 7935 octets.
IEEE80211_HTCAP_MAXAMSDU_3839
Device supports A-MSDU frames up to 3839 octets.
IEEE80211_HTCAP_DSSSCCK40
Device supports use of DSSS/CCK on 40MHz channels.
IEEE80211_HTCAP_PSMP Device supports PSMP.
IEEE80211_HTCAP_40INTOLERANT
Device is intolerant of 40MHz wide channel use.
IEEE80211_HTCAP_LSIGTXOPPROT
Device supports L-SIG TXOP protection.
IEEE80211_HTC_AMPDU Device supports A-MPDU aggregation. Note that any
802.11n compliant device must support A-MPDU
receive so this implicitly means support for
transmit of A-MPDU frames.
IEEE80211_HTC_AMSDU Device supports A-MSDU aggregation. Note that any
802.11n compliant device must support A-MSDU
receive so this implicitly means support for
transmit of A-MSDU frames.
IEEE80211_HTC_HT Device supports High Throughput (HT) operation.
This capability must be set to enable 802.11n
functionality in IEEE80211.
IEEE80211_HTC_SMPS Device supports MIMO Power Save operation.
IEEE80211_HTC_RIFS Device supports Reduced Inter Frame Spacing
(RIFS).
SEE ALSO
ioctl(2), ndis(4), ieee80211_amrr(9), ieee80211_beacon(9),
ieee80211_bmiss(9), ieee80211_crypto(9), ieee80211_ddb(9),
ieee80211_input(9), ieee80211_node(9), ieee80211_output(9),
ieee80211_proto(9), ieee80211_radiotap(9), ieee80211_regdomain(9),
ieee80211_scan(9), ieee80211_vap(9), ifnet(9), malloc(9)
HISTORY
The IEEE80211 series of functions first appeared in NetBSD 1.5, and were
later ported to FreeBSD 4.6. This man page was updated with the
information from NetBSD IEEE80211 man page.
AUTHORS
The original NetBSD IEEE80211 man page was written by Bruce M. Simpson
<bms@FreeBSD.org> and Darron Broad <darron@kewl.org>.
FreeBSD 13.1-RELEASE-p6 December 31, 2017 FreeBSD 13.1-RELEASE-p6
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