1.\" 2.\" Copyright (c) 2009 Sam Leffler, Errno Consulting 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/share/man/man9/ieee80211_beacon.9,v 1.2 2009/09/18 00:33:47 brueffer Exp $ 27.\" 28.Dd April 28, 2010 29.Dt IEEE80211_BEACON 9 30.Os 31.Sh NAME 32.Nm ieee80211_beacon 33.Nd 802.11 beacon support 34.Sh SYNOPSIS 35.In netproto/802_11/ieee80211_var.h 36.Pp 37.Ft "struct mbuf *" 38.Fo ieee80211_beacon_alloc 39.Fa "struct ieee80211_node *" 40.Fa "struct ieee80211_beacon_offsets *" 41.Fc 42.\" 43.Ft int 44.Fo ieee80211_beacon_update 45.Fa "struct ieee80211_node *" 46.Fa "struct ieee80211_beacon_offsets *" 47.Fa "struct mbuf *" 48.Fa "int mcast" 49.Fc 50.\" 51.Ft void 52.Fn ieee80211_beacon_notify "struct ieee80211vap *" "int what" 53.Sh DESCRIPTION 54The 55.Nm net80211 56software layer provides a support framework for drivers that includes 57a template-based mechanism for dynamic update of beacon frames transmit 58in hostap, adhoc, and mesh operating modes. 59Drivers should use 60.Fn ieee80211_beacon_alloc 61to create an initial beacon frame. 62The 63.Vt ieee80211_beacon_offsets 64structure holds information about the beacon contents that is used 65to optimize updates done with 66.Fn ieee80211_beacon_update . 67.Pp 68Update calls should only be done when something changes that 69affects the contents of the beacon frame. 70When this happens the 71.Dv iv_update_beacon 72method is invoked and a driver-supplied routine must do the right thing. 73For devices that involve the host to transmit each 74beacon frame this work may be as simple as marking a bit in the 75.Vt ieee80211_beacon_offsets 76structure: 77.Bd -literal 78static void 79ath_beacon_update(struct ieee80211vap *vap, int item) 80{ 81 struct ieee80211_beacon_offsets *bo = &ATH_VAP(vap)->av_boff; 82 setbit(bo->bo_flags, item); 83} 84.Ed 85.Pp 86with the 87.Fn ieee80211_beacon_update 88call done before the next beacon is to be sent. 89.Pp 90Devices that off-load beacon generation may instead choose to use 91this callback to push updates immediately to the device. 92Exactly how that is accomplished is unspecified. 93One possibility is to update the beacon frame contents and extract 94the appropriate information element, but other scenarios are possible. 95.Sh MULTI-VAP BEACON SCHEDULING 96Drivers that support multiple vaps that can each beacon need to consider 97how to schedule beacon frames. 98There are two possibilities at the moment: 99.Em burst 100all beacons at TBTT or 101.Em stagger beacons 102over the beacon interval. 103Bursting beacon frames may result in aperiodic delivery that can affect 104power save operation of associated stations. 105Applying some jitter (e.g. by randomly ordering burst frames) may be 106sufficient to combat this and typically this is not an issue unless 107stations are using aggressive power save techniques 108such as U-APSD (sometimes employed by VoIP phones). 109Staggering frames requires more interrupts and device support that 110may not be available. 111Staggering beacon frames is usually superior to bursting frames, up to 112about eight vaps, at which point the overhead becomes significant and 113the channel becomes noticeably busy anyway. 114.Sh SEE ALSO 115.Xr ieee80211 9 116