Subject: [Capwap] Issue 151: Are all specified message elements required?

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Thu, 17 Aug 2006 11:11:32 -0700

Are all specified message elements required? (The obvious answer is
"yes", but this document doesn't discuss versioning. For example, what
if in a new version of CAPWAP an additional message element was to be
added. Would a new message type be created and the additional message
element added to it, or the existing type reused?)

<PRC> This is a great question. In the Diameter protocol we dealt with
this issue by including a "Mandatory to implement" bit. If any AVP was
received, whose bit was set, yet was not recognized, then the request
had to be rejected.

We could consider something similar here, but I believe with the
firmware download component of the protocol it may be less of an issue -
although not guaranteed. I would hope (and expect) that as the CAPWAP
protocol extends, the AC would push new firmware to the WTP. This does
require that the initial part of the state machine be fairly static, and
this could be an area where the "Mandatory to implement" bit could be
useful as it would allow the AC to fall back to older protocol behavior.

That said, I know that my company has made significant improvments to
the orignally proposed protocol, and this has never been an issue.

Thoughts? Is this a mandatory feature, or a nice to have? I'd reluctant
to
add nice to have features at this point.

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems
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