/share/man/man9/ieee80211_beacon.9

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  1. .\"
  2. .\" Copyright (c) 2009 Sam Leffler, Errno Consulting
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  28. .Dd August 4, 2009
  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 net80211/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
  54. The
  55. .Nm net80211
  56. software layer provides a support framework for drivers that includes
  57. a template-based mechanism for dynamic update of beacon frames transmit
  58. in hostap, adhoc, and mesh operating modes.
  59. Drivers should use
  60. .Fn ieee80211_beacon_alloc
  61. to create an initial beacon frame.
  62. The
  63. .Vt ieee80211_beacon_offsets
  64. structure holds information about the beacon contents that is used
  65. to optimize updates done with
  66. .Fn ieee80211_beacon_update .
  67. .Pp
  68. Update calls should only be done when something changes that
  69. affects the contents of the beacon frame.
  70. When this happens the
  71. .Dv iv_update_beacon
  72. method is invoked and a driver-supplied routine must do the right thing.
  73. For devices that involve the host to transmit each
  74. beacon frame this work may be as simple as marking a bit in the
  75. .Vt ieee80211_beacon_offsets
  76. structure:
  77. .Bd -literal
  78. static void
  79. ath_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
  86. with the
  87. .Fn ieee80211_beacon_update
  88. call done before the next beacon is to be sent.
  89. .Pp
  90. Devices that off-load beacon generation may instead choose to use
  91. this callback to push updates immediately to the device.
  92. Exactly how that is accomplished is unspecified.
  93. One possibility is to update the beacon frame contents and extract
  94. the appropriate information element, but other scenarios are possible.
  95. .Sh MULTI-VAP BEACON SCHEDULING
  96. Drivers that support multiple vaps that can each beacon need to consider
  97. how to schedule beacon frames.
  98. There are two possibilities at the moment:
  99. .Em burst
  100. all beacons at TBTT or
  101. .Em stagger beacons
  102. over the beacon interval.
  103. Bursting beacon frames may result in aperiodic delivery that can affect
  104. power save operation of associated stations.
  105. Applying some jitter (e.g. by randomly ordering burst frames) may be
  106. sufficient to combat this and typically this is not an issue unless
  107. stations are using aggressive power save techniques
  108. such as U-APSD (sometimes employed by VoIP phones).
  109. Staggering frames requires more interrupts and device support that
  110. may not be available.
  111. Staggering beacon frames is usually superior to bursting frames, up to
  112. about eight vaps, at which point the overhead becomes significant and
  113. the channel becomes noticeably busy anyway.
  114. .Sh SEE ALSO
  115. .Xr ieee80211 9