Subject: [Capwap] Issue 53: Add Data Rate to LWAPP Header

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Mon, 1 May 2006 14:46:30 -0700

All,

The following is a proposed new CAPWAP header format, as a result of
discussions on the list. Comments are most welcomed.

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.
 
      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  |W|F|L|M|          Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Fragment ID          |     Frag Offset         |Rsv-2|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 (optional) Radio MAC Address                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |            (optional) Wireless Specific Information           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        Payload ....                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
4.1.1.  VERSION Field
 
   A 4 bit field which contains the version of CAPWAP used in this
   packet.  The value for this draft is 0.
 
4.1.2.  RID Field
 
   A 5 bit field which contains the Radio ID number for this packet.
   WTPs with multiple radios but a single MAC Address use this field to
   indicate which radio is associated with the packet.
 
4.1.3.  HLEN
   Length of CAPWAP tunnel header in 4 byte words. (Similar to IP
   header length). This length includes the optional headers.

4.1.4.  W Bit
 
   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.

4.1.5.  F Bit
 
   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.
 
4.1.6.  L Bit
 
   The Not 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 not the last fragment.  When this bit is 0, the packet is
   the last fragment.

4.1.7.  M Bit
 
   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.

4.1.8.  Reserved
 
   The 15-bit Reserved field is reserved and set to 0 in this version of
the 
   CAPWAP protocol.
  
4.1.9. 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.  
 
4.1.10. 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. 
 
4.1.11.  Reserved-2
 
   The 3-bit Reserved-2 field is reserved and set to 0 in this version
of the 
   CAPWAP protocol.

4.1.12.  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.

   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:  MAC Address of the receiving radio

4.1.13.  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.

   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 binding section.

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

[...]

11.3.2.  CAPWAP Wireless Specific Information

   The reserved CAPWAP header field (see figure 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 Section 11.3.2.1.  However,
   for frames sent by the AC to the WTP, the format used is described in
   described in Section 11.3.2.2.

11.3.2.1.  IEEE 802.11 Frame Info

   When an CAPWAP data frame is received from a station over the air, it
   is encapsulated and this field is used to include radio and PHY
   specific information associated with the frame.

   When used with the IEEE 802.11 binding, the field follows 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     RSSI      |     SNR       |           Data Rate           | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   RSSI:  RSSI is a signed, 8-bit value.  It is the received signal
      strength indication, in dBm.

   SNR:  SNR is a signed, 8-bit value.  It is the signal to noise ratio
      of the received IEEE 802.11 frame, in dB.

   Data Rate:  The data rate field is a 16 bit unsigned value.  The
      contents of the field is set to 1/10th of the data rate of the
      packet received by the WTP.  For instance, a packet received at  
 
[Rest is identical to -00]

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems
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From: Jim Murphy <[email-masked]>
Date: Thu, 04 May 2006 14:40:28 -0700

Pat,

Looks great. Any chance we can get a payload type in the header?
It would be nice for a switching system to be able to switch
arbitrary payload types (802.11, 802.3, etc.). I think 8 bits
from your Reserved field would suffice.

Thanks,

Jim