NAME

       ieee80211_output — software 802.11 stack output functions

SYNOPSIS

       #include <net80211/ieee80211_var.h>

       int
       M_WME_GETAC(struct mbuf *);

       int
       M_SEQNO_GET(struct mbuf *);

       struct ieee80211_key *
       ieee80211_crypto_encap(struct ieee80211_node *, struct mbuf *);

       void
       ieee80211_process_callback(struct ieee80211_node *, struct mbuf *, int);

DESCRIPTION

       The  net80211  layer  that  supports  802.11 device drivers handles most of the work required to transmit
       frames.  Drivers usually receive fully-encapsulated 802.11 frames that have been classified and  assigned
       a transmit priority; all that is left is to do crypto encapsulation, prepare any hardware-specific state,
       and  push the packet out to the device.  Outbound frames are either generated by the net80211 layer (e.g.
       management frames) or are passed down from upper layers through the ifnet(9) transmit queue.  Data frames
       passed down for transmit flow through net80211 which handles aggregation, 802.11 encapsulation, and  then
       dispatches the frames to the driver through it's transmit queue.

       There  are two control paths by which frames reach a driver for transmit.  Data packets are queued to the
       device's if_snd queue and the driver's if_start method is called.  Other frames are passed down using the
       ic_raw_xmit method without queueing (unless done by the driver).  The raw transmit path may include  data
       frames  from  user applications that inject them through bpf(4) and NullData frames generated by net80211
       to probe for idle stations (when operating as an access point).

       net80211 handles all state-related bookkeeping and management for the  handling  of  data  frames.   Data
       frames  are only transmit for a vap in the IEEE80211_S_RUN state; there is no need, for example, to check
       for frames sent down when CAC  or  CSA  is  active.   Similarly,  net80211  handles  activities  such  as
       background  scanning  and  power save mode, frames will not be sent to a driver unless it is operating on
       the BSS channel with “full power”.

       All frames passed to a driver for transmit hold a reference to a node table entry in  the  m_pkthdr.rcvif
       field.   The  node is associated with the frame destination.  Typically it is the receiver's entry but in
       some situations it may be a placeholder entry or the “next hop station” (such as in a mesh network).   In
       all cases the reference must be reclaimed with ieee80211_free_node() when the transmit work is completed.
       The  rule  to remember is: net80211 passes responsibility for the mbuf and “node reference” to the driver
       with each frame it hands off for transmit.

PACKET CLASSIFICATION

       All frames passed by net80211 for transmit are assigned a priority based on any vlan tag assigned to  the
       receiving  station  and/or  any  Diffserv  setting  in  an  IP or IPv6 header.  If both vlan and Diffserv
       priority are present the higher of the two is used.  If WME/WMM is being used then  any  ACM  policy  (in
       station  mode) is also enforced.  The resulting AC is attached to the mbuf and may be read back using the
       M_WME_GETAC() macro.

       PAE/EAPOL frames are tagged with an M_EAPOL mbuf flag; drivers should transmit them with care, usually by
       using the transmit rate for management frames.  Multicast/broadcast frames are marked  with  the  M_MCAST
       mbuf  flag.   Frames  coming  out  of  a station's power save queue and that have more frames immediately
       following are marked with the M_MORE_DATA mbuf flag.  Such frames will be  queued  consecutively  in  the
       driver's if_snd queue and drivers should preserve the ordering when passing them to the device.

FRAGMENTED FRAMES

       The  net80211  layer  will  fragment data frames according to the setting of iv_fragthreshold if a driver
       marks the IEEE80211_C_TXFRAG capability.  Fragmented frames are placed in the devices transmit queue with
       the fragments chained together with m_nextpkt.  Each frame is marked with the M_FRAG mbuf flag,  and  the
       first and last are marked with M_FIRSTFRAG and M_LASTFRAG, respectively.  Drivers are expected to process
       all fragments or none.

TRANSMIT CALLBACKS

       Frames  sent  by  net80211  may be tagged with the M_TXCB mbuf flag to indicate a callback should be done
       when their transmission completes.  The callback is done using ieee80211_process_callback() with the last
       parameter set to a non-zero value if an error occurred and zero  otherwise.   Note  net80211  understands
       that  drivers may be incapable of determining status; a device may not report if an ACK frame is received
       and/or a device may queue transmit requests in its hardware and only report status on whether  the  frame
       was successfully queued.

SEE ALSO

       bpf(4), ieee80211(9), ifnet(9)

Debian                                           March 29, 2010                              IEEE80211_OUTPUT(9)