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+
+References:
+* http://www.rfc-editor.org/rfc/rfc5415.txt
+
+
+The CAPWAP header layout is summarized as follows:
+
+
+        0                   1                   2                   3
+        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |CAPWAP Preamble|  HLEN   |   RID   | WBID    |T|F|L|W|M|K|Flags|
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |          Fragment ID          |     Frag Offset         |Rsvd |
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |                 (optional) Radio MAC Address                  |
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |            (optional) Wireless Specific Information           |
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |                        Payload ....                           |
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+The spec defines an optional Wireless Specific Information field which can be
+used to pass arbitrary data in the encapsulation layer:
+
+   Wireless Specific Information:  This optional field may be used to carry
+      per-packet information.  This field is only present if the
+      'W' bit is set.  The WBID field in the CAPWAP Header is used to
+      identify the format of the WSI optional field. The HLEN field assumes
+      4-byte alignment, and this field MUST be padded with zeroes (0x00) if it
+      is not 4-byte aligned.
+
+      The Wireless-Specific Information field uses the following format:
+
+        0                   1                   2                   3
+        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |    Length     |                Data...
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+      Length:  The 8-bit field contains the length of the data field,
+         with a maximum size of 255.
+
+      Data:  Wireless-specific information, defined by the wireless-
+         specific binding specified in the CAPWAP Header's WBID field.
+
+
+   WBID:  A 5-bit field that is the wireless binding identifier.  The
+      identifier will indicate the type of wireless packet associated
+      with the radio.  The following values are defined:
+
+      0 -  Reserved
+      1 -  IEEE 802.11
+      2 -  Reserved
+      3 -  EPCGlobal [EPCGlobal]
+
+      When Open vSwitch uses this field, it writes the value:
+      30 - Open vSwitch data
+
+
+Open vSwitch can make use of this field to pass additional packet routing
+information. When needed, it sets the 'W' bit to indicates the WSI field is
+added, and fills the field as follows:
+
+        0                   1                   2                   3
+        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |  WSI_LEN      |K|      Flags  |             Reserved          |
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+       |   (optional) 64bit Tunnel Key                                 |
+       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+       K - flag bit to identify presence of a 64bit tunnel key.
+
+
+Adding WSI fields:  Fields must be written and read in consitent order.  New
+fields may be added, but the existing fields always come first.