Subject: [Capwap] Proposed Resolution for Issue 120: Issues with new CAPWAP header format AND Issue 119: Add encapsulated data type in CAPWAP data header

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Mon, 22 May 2006 08:22:31 -0700

All,

Please see issues 120 and 119 for the various issues with the new header
text in the -01 draft. Below are my proposed changes, which I would like
to get some comments on.

4.1.  CAPWAP Transport Header

   All CAPWAP protocol messages are encapsulated using a common header
   format, regardless of the CAPWAP control or CAPWAP Data transport
   used to carry the messages.  However, certain flags are not
   applicable for a given transport.  Refer to the specific transport
   section in order to determine which flags are valid.

   Note that the optional fields defined in this section MUST be present
   in the precise order shown below.

         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
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |Version|   RID   |  HLEN   |  WBID   |T|F|L|W|M|     Flags
|
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |          Fragment ID          |     Frag Offset         |Rsvd
|
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                 (optional) Radio MAC Address
|
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |            (optional) Wireless Specific Information
|
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |                        Payload ....
|
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Version: A 4 bit field which contains the version of CAPWAP used in
      this packet.  The value for this draft is 0.

   RID: A 5 bit field which contains the Radio ID number for this
      packet.  WTPs with multiple radios but a single MAC Address range
      use this field to indicate which radio is associated with the
      packet.

   HLEN: A 5 bit field containing the length of the CAPWAP transport
      header in 4 byte words (Similar to IP header length).  This length
      includes the optional headers.

   WBID: A 5 bit field which is the wireless binding identifier.  The
      identifier will indicate the type of wireless packet type
      associated with the radio.  The following values are defined:

      1 - IEEE 802.11

   T: The Type 'T' bit indicates the format of the frame being
      transported in the payload (see Section 11.4).  When this bit is
      set to one (1), the payload has the native frame format indicated
      by the WBID field.  When this bit is zero (0) the payload is an
      IEEE 802.3 frame.

   F: The Fragment 'F' bit indicates whether this packet is a fragment.
      When this bit is one (1), the packet is a fragment and MUST be
      combined with the other corresponding fragments to reassemble the
      complete information exchanged between the WTP and AC.

   L: The Last 'L' bit is valid only if the 'F' bit is set and indicates
      whether the packet contains the last fragment of a fragmented
      exchange between WTP and AC.  When this bit is 1, the packet is
      the last fragment.  When this bit is 0, the packet is not the last
      fragment.

   W: The Wireless 'W' bit is used to specify whether the optional
      wireless specific information field is present in the header.  A
      value of one (1) is used to represent the fact that the optional
      header is present.

   M: The M bit is used to indicate that the Radio MAC Address optional
      header is present.  This is used to communicate the MAC address of
      the receiving radio when the native wireless packet.  This field
      MUST NOT be set to one in packets sent by the AC to the WTP.

   Flags: A set of reserved bits for future flags in the CAPWAP header.
      All implementations complying with version zero of this protocol
      MUST set these bits to zero.

   Fragment ID: An 16 bit field whose value is assigned to each group of
      fragments making up a complete set.  The fragment ID space is
      managed individually for every WTP/AC pair.  The value of Fragment
      ID is incremented with each new set of fragments.  The Fragment ID
      wraps to zero after the maximum value has been used to identify a
      set of fragments.

   Fragment Offset: A 13 bit field that indicates where in the payload
      will this fragment belong during re-assembly.  This field is valid
      when the 'F' bit is set to 1.  The fragment offset is measured in
      units of 8 octets (64 bits).  The first fragment has offset zero.
      Note the CAPWAP protocol does not allow for overlapping fragments.
      For instance, fragment 0 would include offset 0 with a payload
      length of 1000, while fragment 1 include offset 900 with a payload
      length of 600.

   Reserved: The 3-bit Reserved field is reserved and set to 0 in this
      version of the CAPWAP protocol.

   Radio MAC Address: This optional field contains the MAC address of
      the radio receiving the packet.  This is useful in packets sent
      from the WTP to the AC, when the native wireless frame format is
      converted to 802.3 by the WTP.  This field is only present if the
      'M' bit is set.  Given the HLEN field assumes 4 byte alignment,
      this field MUST be padded with zeroes (0x00) if it is not 4 byte
      aligned.

      The field contains the basic 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     |                  MAC Address
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Length: The number of bytes in the MAC Address field.  The length
         field is present since new IEEE technologies are using 48 byte
         MAC addresses.

      MAC Address: The MAC Address of the receiving radio.

   Wireless Specific Information: This optional field contains
      technology specific information that may be used to carry per
      packet wireless information.  This field is only present if the
      'W' bit is set.  Given the HLEN field assumes 4 byte alignment,
      this field MUST be padded with zeroes (0x00) if it is not 4 byte
      aligned.

      The field contains the basic 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
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |  Wireless ID  |    Length     |             Data
 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Wireless ID: The wireless binding identifier.  The following
         values are defined:

         1 - : IEEE 802.11

      Length: The length of the data field

      Data: Wireless specific information, whose details are defined in
         the technology specific bindings section (see Section 11.4.

   Payload: This field contains the header for a CAPWAP Data Message or
      CAPWAP Control Message, followed by the data associated with that
      message.

[...] 

11.4.  Technology Specific Bindings

   All CAPWAP transports have the following IEEE 802.11 specific
   bindings:

[...]
   Optional Wireless Specific Information The optional CAPWAP header
      field (see Section 4.1) is only used with CAPWAP data frames, and
      it serves two purposes, depending upon the direction of the frame.
      For packets from the WTP to the AC, the field uses the format
      described in the "IEEE 802.11 Frame Info" field (see below).
      However, for frames sent by the AC to the WTP, the format used is
      described in described in the "Destination WLANs" field (also
      defined below).
[...]

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems
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