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<table class="head">
<tr>
<td class="head-ltitle">IEEE80211_BEACON(9)</td>
<td class="head-vol">Kernel Developer's Manual</td>
<td class="head-rtitle">IEEE80211_BEACON(9)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">ieee80211_beacon</code> —
<span class="Nd">802.11 beacon support</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><code class="In">#include
<<a class="In">net80211/ieee80211_var.h</a>></code></p>
<p class="Pp">
<br/>
<var class="Ft">struct mbuf *</var>
<br/>
<code class="Fn">ieee80211_beacon_alloc</code>(<var class="Fa">struct
ieee80211_node *</var>, <var class="Fa">struct ieee80211_beacon_offsets
*</var>);</p>
<p class="Pp"><var class="Ft">int</var>
<br/>
<code class="Fn">ieee80211_beacon_update</code>(<var class="Fa">struct
ieee80211_node *</var>, <var class="Fa">struct ieee80211_beacon_offsets
*</var>, <var class="Fa">struct mbuf *</var>, <var class="Fa">int
mcast</var>);</p>
<p class="Pp"><var class="Ft">void</var>
<br/>
<code class="Fn">ieee80211_beacon_notify</code>(<var class="Fa" style="white-space: nowrap;">struct
ieee80211vap *</var>, <var class="Fa" style="white-space: nowrap;">int
what</var>);</p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">The <code class="Nm">net80211</code> software layer provides a
support framework for drivers that includes a template-based mechanism for
dynamic update of beacon frames transmit in hostap, adhoc, and mesh
operating modes. Drivers should use
<a class="permalink" href="#ieee80211_beacon_alloc"><code class="Fn" id="ieee80211_beacon_alloc">ieee80211_beacon_alloc</code></a>()
to create an initial beacon frame. The
<var class="Vt">ieee80211_beacon_offsets</var> structure holds information
about the beacon contents that is used to optimize updates done with
<code class="Fn">ieee80211_beacon_update</code>().</p>
<p class="Pp">Update calls should only be done when something changes that
affects the contents of the beacon frame. When this happens the
<code class="Dv">iv_update_beacon</code> method is invoked and a
driver-supplied routine must do the right thing. For devices that involve
the host to transmit each beacon frame this work may be as simple as marking
a bit in the <var class="Vt">ieee80211_beacon_offsets</var> structure:</p>
<div class="Bd Pp Li">
<pre>static void
ath_beacon_update(struct ieee80211vap *vap, int item)
{
struct ieee80211_beacon_offsets *bo = &ATH_VAP(vap)->av_boff;
setbit(bo->bo_flags, item);
}</pre>
</div>
<p class="Pp" id="ieee80211_beacon_update">with the
<a class="permalink" href="#ieee80211_beacon_update"><code class="Fn">ieee80211_beacon_update</code></a>()
call done before the next beacon is to be sent.</p>
<p class="Pp">Devices that off-load beacon generation may instead choose to use
this callback to push updates immediately to the device. Exactly how that is
accomplished is unspecified. One possibility is to update the beacon frame
contents and extract the appropriate information element, but other
scenarios are possible.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="MULTI-VAP_BEACON_SCHEDULING"><a class="permalink" href="#MULTI-VAP_BEACON_SCHEDULING">MULTI-VAP
BEACON SCHEDULING</a></h1>
<p class="Pp">Drivers that support multiple vaps that can each beacon need to
consider how to schedule beacon frames. There are two possibilities at the
moment:
<a class="permalink" href="#burst"><i class="Em" id="burst">burst</i></a>
all beacons at TBTT or
<a class="permalink" href="#stagger"><i class="Em" id="stagger">stagger
beacons</i></a> over the beacon interval. Bursting beacon frames may result
in aperiodic delivery that can affect power save operation of associated
stations. Applying some jitter (e.g. by randomly ordering burst frames) may
be sufficient to combat this and typically this is not an issue unless
stations are using aggressive power save techniques such as U-APSD
(sometimes employed by VoIP phones). Staggering frames requires more
interrupts and device support that may not be available. Staggering beacon
frames is usually superior to bursting frames, up to about eight vaps, at
which point the overhead becomes significant and the channel becomes
noticeably busy anyway.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">ieee80211(9)</a></p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">August 4, 2009</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
