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: head/share/man/man9/ieee80211_beacon.9 197300 2009-09-18 00:33:47Z brueffer $ 27.\" 28.Dd May 26, 2016 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 net/if.h 36.In net/if_media.h 37.In netproto/802_11/ieee80211_var.h 38.Pp 39.Ft "struct mbuf *" 40.Fo ieee80211_beacon_alloc 41.Fa "struct ieee80211_node *" 42.Fc 43.\" 44.Ft int 45.Fo ieee80211_beacon_update 46.Fa "struct ieee80211_node *" 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. 62.Pp 63Update calls should only be done when something changes that 64affects the contents of the beacon frame. 65When this happens the 66.Dv iv_update_beacon 67method is invoked and a driver-supplied routine must do the right thing. 68For devices that involve the host to transmit each 69beacon frame this work may be as simple as marking a bit in the 70.Vt ieee80211_beacon_offsets 71structure: 72.Bd -literal 73static void 74ath_beacon_update(struct ieee80211vap *vap, int item) 75{ 76 struct ieee80211_beacon_offsets *bo = &ATH_VAP(vap)->av_boff; 77 setbit(bo->bo_flags, item); 78} 79.Ed 80.Pp 81with the 82.Fn ieee80211_beacon_update 83call done before the next beacon is to be sent. 84.Pp 85Devices that off-load beacon generation may instead choose to use 86this callback to push updates immediately to the device. 87Exactly how that is accomplished is unspecified. 88One possibility is to update the beacon frame contents and extract 89the appropriate information element, but other scenarios are possible. 90.Sh MULTI-VAP BEACON SCHEDULING 91Drivers that support multiple vaps that can each beacon need to consider 92how to schedule beacon frames. 93There are two possibilities at the moment: 94.Em burst 95all beacons at TBTT or 96.Em stagger beacons 97over the beacon interval. 98Bursting beacon frames may result in aperiodic delivery that can affect 99power save operation of associated stations. 100Applying some jitter (e.g. by randomly ordering burst frames) may be 101sufficient to combat this and typically this is not an issue unless 102stations are using aggressive power save techniques 103such as U-APSD (sometimes employed by VoIP phones). 104Staggering frames requires more interrupts and device support that 105may not be available. 106Staggering beacon frames is usually superior to bursting frames, up to 107about eight vaps, at which point the overhead becomes significant and 108the channel becomes noticeably busy anyway. 109.Sh SEE ALSO 110.Xr ieee80211 9 111