116 lines
4.2 KiB
Groff
116 lines
4.2 KiB
Groff
.\"
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.\" Copyright (c) 2009 Sam Leffler, Errno Consulting
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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_BEACON 9
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.Os
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.Sh NAME
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.Nm ieee80211_beacon
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.Nd 802.11 beacon support
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.Sh SYNOPSIS
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.In net80211/ieee80211_var.h
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.Pp
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.Ft "struct mbuf *"
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.Fo ieee80211_beacon_alloc
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.Fa "struct ieee80211_node *"
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.Fa "struct ieee80211_beacon_offsets *"
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.Fc
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.\"
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.Ft int
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.Fo ieee80211_beacon_update
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.Fa "struct ieee80211_node *"
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.Fa "struct ieee80211_beacon_offsets *"
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.Fa "struct mbuf *"
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.Fa "int mcast"
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.Fc
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.\"
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.Ft void
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.Fn ieee80211_beacon_notify "struct ieee80211vap *" "int what"
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.Sh DESCRIPTION
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The
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.Nm net80211
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software layer provides a support framework for drivers that includes
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a template-based mechanism for dynamic update of beacon frames transmit
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in hostap, adhoc, and mesh operating modes.
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Drivers should use
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.Fn ieee80211_beacon_alloc
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to create an initial beacon frame.
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The
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.Vt ieee80211_beacon_offsets
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structure holds information about the beacon contents that is used
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to optimize updates done with
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.Fn ieee80211_beacon_update .
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.Pp
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Update calls should only be done when something changes that
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affects the contents of the beacon frame.
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When this happens the
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.Dv iv_update_beacon
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method is invoked and a driver-supplied routine must do the right thing.
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For devices that involve the host to transmit each
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beacon frame this work may be as simple as marking a bit in the
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.Vt ieee80211_beacon_offsets
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structure:
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.Bd -literal
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static void
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ath_beacon_update(struct ieee80211vap *vap, int item)
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{
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struct ieee80211_beacon_offsets *bo = &ATH_VAP(vap)->av_boff;
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setbit(bo->bo_flags, item);
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}
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.Ed
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.Pp
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with the
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.Fn ieee80211_beacon_update
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call done before the next beacon is to be sent.
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.Pp
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Devices that off-load beacon generation may instead choose to use
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this callback to push updates immediately to the device.
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Exactly how that is accomplished is unspecified.
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One possibility is to update the beacon frame contents and extract
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the appropriate information element, but other scenarios are possible.
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.Sh MULTI-VAP BEACON SCHEDULING
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Drivers that support multiple vaps that can each beacon need to consider
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how to schedule beacon frames.
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There are two possibilities at the moment:
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.Em burst
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all beacons at TBTT or
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.Em stagger beacons
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over the beacon interval.
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Bursting beacon frames may result in aperiodic delivery that can affect
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power save operation of associated stations.
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Applying some jitter (e.g. by randomly ordering burst frames) may be
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sufficient to combat this and typically this is not an issue unless
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stations are using aggressive power save techniques
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such as U-APSD (sometimes employed by VoIP phones).
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Staggering frames requires more interrupts and device support that
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may not be available.
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Staggering beacon frames is usually superior to bursting frames, up to
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about eight vaps, at which point the overhead becomes significant and
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the channel becomes noticeably busy anyway.
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.Sh SEE ALSO
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.Xr ieee80211 9
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