Capwap Mailing List: RE: Proposed Text for Issue 53

[Abhijit Choudhury (Abhijit]

Title: Message

The default mode is not the only issue. As Bob has
pointed out some AC implementations may use per-packet

receive info for value added functionalities.  Some others
may use transmit info (like number of retries, transmit
rate) to do similar services and prefer that instead
or in addition.  And some may be prefer the WTP to do

the aggregation.  So, now do we keep adding all this

additional fields into the CAPWAP header ?

Based on our current discussion, I would suggest having
extension capabilities in the CAPWAP header. The current

CAPWAP header can be the default header. (Note that we need

a 6 byte CAPWAP header for AC -> WTP direction as we need

the WLAN ID field. So, we can also carry RSSI/SNR for free).

Below are some possibilities :

1. We can use the VER (version) field for this .
For example, the current CAPWAP header can be VER 0.
Now if someone needs data rate or other stats,

we can define different size fields
(2bytes, 6 bytes etc) with the other encodings of VER.
This gives us the flexbility to do carry additional
information if the implementation needs it.
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0| RID |F|L|R|    Frag ID    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     RSSI      |     SNR       |           Payload....         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 1| RID |F|L|R|    Frag ID    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     RSSI      |     SNR       |           Data Rate           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Payload...  |
     +-+-+-+-+-+-+-+-+

2. Alternatively, we can use the current R bit as an option
flag (like L2TP). Data Rate (new D bit) could be a flag
and if set, would indicate a 2 byte field at the end
that carries data rate.

D=0      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |VER| RID |F|L|D|    Frag ID    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     RSSI      |     SNR       |           Payload....         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

D=1
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |VER| RID |F|L|D|    Frag ID    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     RSSI      |     SNR       |           Data Rate           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Payload...  |
     +-+-+-+-+-+-+-+-+

With this approach, we will have the flexibility to carry additional

information if we need it on a per-packet basis, and only the default

header if we don't need it or are allowing the WTP to aggregate information.

We will not need to make it mandatory for everyone to carry additional

information.

Comments ?

Thanks,
   Abhijit




-----Original Message-----
From: Puneet Agarwal [mailto:pagarwal [at] broadcom.com]
Sent: Wednesday, April 05, 2006 3:49 PM
To: Bob O'Hara (boohara); capwap
Subject: RE: [Capwap] Proposed Text for Issue 53


Hi Bob,

It seems the real issue is what is the default mode of operation.

Summary:
---------

Pat/Bob: Carry the phy info in every CAPWAP data pkt as at least 1 implementation uses it
Abhijit/Saravanan: Carry phy info in control msgs periodically and not in every CAPWAP data frame.

My Proposal (Compromise):
-------------------------
Sending the Phy info (RSSI/SNR/Speed) should be optional. By default this info should *NOT* be sent in every CAPWAP data packet. This capability should be negotiated at WTP<->AC handshake time.

Comments?

Thanks.

-Puneet


-----Original Message-----
From: Bob O'Hara (boohara) [mailto:boohara [at] cisco.com]
Sent: Wednesday, April 05, 2006 7:15 AM
To: capwap
Subject: RE: [Capwap] Proposed Text for Issue 53

For those AC implementations that want to use per packet data for certain operations, aggregation of the data at the WTP as suggested by Abhijit will preclude this.  The assertion by Saravanan that an AC does not process this information is incorrect.  I can point to at least one existing implementation that already does process this information on a per packet basis.

The current text, with the change I suggested, is the right way to handle this.  If we want to ADD a capability that the WTP can provide aggregation, I have no objection to that.

 -Bob

-----Original Message-----
From: Saravanan Govindan [mailto:Saravanan.Govindan [at] sg.panasonic.com]
Sent: Tuesday, April 04, 2006 4:49 PM
To: Abhijit Choudhury; Pat Calhoun (pacalhou); capwap
Subject: RE: [Capwap] Proposed Text for Issue 53

Hi Abhijit,

I am in support of your suggestion. It is true that the AC does not process all data packets. Furthermore, I think for greater control, the AC will need information about the congestion level in the WLAN. This could be a derivative of interference and load factor.

As for your suggestion, I think measurement/parameter information from the WTP should be sent over the periodic Echo Request messages. The advantage is that header overhead is reduced.

I can prepare text for this approach.

Cheers,

Saravanan





-----Original Message-----
From: Abhijit Choudhury [mailto:Abhijit [at] sinett.com]
Sent: Wednesday, April 05, 2006 6:52 AM
To: Pat Calhoun (pacalhou); capwap
Subject: RE: [Capwap] Proposed Text for Issue 53

Here's another approach...

RSSI, SNR, and Data Rate are measurements/parameters of the radio channel that are being reported to the AC for finer control.  Carrying them in every data packet on the data channel means some logic or hardware in the AC will have to parse them out of every data packet and send them to the control path (CPU).  Typically not every packet will go to the CPU and so this data will have to be stored and periodically sent to or read by the CPU.  Note that the AC will be possibly dealing with tens to hundreds of WTPs and hence a potentially large number of STAs. This implies a large amount of per-STA measurement data has to be stored and moved from the data path to the CPU.

A more reasonable approach is to let the WTP aggregate such data and periodically send it in the control channel to the AC.  Note the WTP has to deal with much much fewer clients - so the storage burden is less. All we'd need is a frame that carries this information to the AC at a specified interval of time.  This period could be configurable.

Using this approach, we don't need to increase the CAPWAP header every time we need new measurement info. We can retain the current CAPWAP header and flexibly add any measurement information we need by adding it in the control channel. This is particularly important as we move forward to support 802.11n or other non-802.11 technlogies. It decouples the CAPWAP header from the measurement data related information.

Any thoughts on this ?


Thanks,
   Abhijit




-----Original Message-----
From: Pat Calhoun (pacalhou) [mailto:pcalhoun [at] cisco.com]
Sent: Monday, April 03, 2006 8:45 PM
To: capwap
Subject: [Capwap] Proposed Text for Issue 53


Here is my proposed text for Issue 53, which is the addition of a Data Rate In the CAPWAP header.

Please let me know if you have any comments.

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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |VER| RID |F|L|R|    Frag ID    |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Reserved                            |
<=== CHANGED!!!
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Payload...  |
     +-+-+-+-+-+-+-+-+

[...]
4.1.8.  Reserved

   This 32 bit field is reserved and may be used by a binding specific
   extension.  Refer to the transport portion of the binding for a
   specific wireless technology for the definition of this field.

[...]

11.3.2.  CAPWAP Header Reserved field

   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
      5.5Mbps would be set to 55, while 11Mbps would be set to 110.

11.3.2.2.  Destination WLANs

   The Destination WLAN field is used to specify the target WLANs for a
   given frame, and is only used with broadcast and multicast frames.
   This field allows the AC to transmit a single broadcast or multicast
   frame to the WTP, and allows the WTP to perform the necessary frame
   replication services.  The 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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              WLAN             |            Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   WLAN:  This bit field indicates the WLAN ID (see section
      Section 11.8.1.1) which the WTP will transmit the associated frame
      on.  For instance, if a multicast packet is to be transmitted on
      WLANs 1 and 3, bits 1 and 3 of this field would be enabled.  Note
      this field is to be set to zero for unicast packets and is unused
      if the WTP is not providing encryption services.

   Reserved:  This field MUST be set to zero.



Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems _________________________________________________________________
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