Subject: Re: [Capwap] CAPWAP clarifications

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Mon, 2 Jun 2008 08:39:48 -0700

See below.

PatC 

-----Original Message-----
From: Vishal Study [mailto:[email-masked]] 
Sent: Thursday, May 29, 2008 8:34 AM
To: [email-masked]
Subject: [Capwap] CAPWAP clarifications

Hello everyone:

I'm new to CAPWAP world and have some questions on
draft-ietf-capwap-protocol-specification-10.txt:

- It talks about Local and Split MAC functionality.
  Should both modes must be supported? Which one is the most commonly
used?
<PRC> The spec says that WTPs MUST support Local mode, while Split mode
is optional.

- What is the typical pkt size between WTP and AC? Is it 1500B?
<PRC> Section 2.3.2.1 says:
   o  DTLSMtuUpdate is sent by the CAPWAP component to modify the MTU
      size used by the DTLS component.  See Section 3.5 for more
      information on MTU Discovery.  The default size is 1468 bytes.

<PRC> I would also point you to the MTU Discovery, section 3.5.

- Typically, how many WTPs are supported by a single AC?
<PRC> Not a standards issue, and therefore not relevant for this list.

- At WTP, all 802.11 data packets are tunnelled using CAPWAP hdr and
sent over wired interface to AC. i.e. all packets from STA *must* be
sent to AC by WTP. WTP can't route the pkts by itself?
Is that correct?
<PRC> Local mode means the WTP routes/bridges packets natively - no
tunneling. The "IEEE 802.11 Binding" section in the 802.11 binding
document will provide the info you are looking for.

- UpLink traffic - AC does the following to forward a Plain text data
pkt (i.e. IP/UDP/CAPWAP-hdr/Wireless Payload)
  - process IP/UDP
  - extract final Destination information from CAPWAP-hdr
  - route pkt to final destination
<PRC> See the section I pointed you to above, as this will also be
covered.

  So, the data rate performance of AC is tied to how fast it can do the
above (i.e. UDP/IP processing, route lookup and forwarding).
  If secured, AC needs to do AES-128 operations as well.
<PRC> If the AC is sitting in the data path, then yes, its performance
can be the limiting factor. Encryption of the data plane is optional.
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From: "Puneet Agarwal" <[email-masked]>
Date: Fri, 13 Jun 2008 15:14:53 -0700

Minor nit:

Section 1 of -10 spec (pg 7):
"The Local MAC mode of operation allows for the data frames to be
   either locally bridged, or tunneled as 802.3 frames.  The latter
   implies that the WTP performs the 802.11 Integration function.  In
   either case the L2 wireless management frames are processed locally
   by the WTP, and then forwarded to the AC."

Thanks.

-Puneet

-----Original Message-----
From: Pat Calhoun (pacalhou) [mailto:[email-masked]] 
Sent: Monday, June 02, 2008 8:40 AM
To: Vishal Study; [email-masked]
Subject: Re: [Capwap] CAPWAP clarifications

See below.

PatC 

-----Original Message-----
From: Vishal Study [mailto:[email-masked]]
Sent: Thursday, May 29, 2008 8:34 AM
To: [email-masked]
Subject: [Capwap] CAPWAP clarifications

Hello everyone: