draft-chiba compatibility with Diameter

[Bernard Aboba <aboba@internaut.com>]

A question has recently arisen in the AAA WG regarding translation of CoA
and Disconnect messages to and from Diameter.

It appears that existing implementations of draft-chiba are tricky (or in
some cases impossible) to translate due to the differences in usage model.

In response to a thread on the AAA WG mailing list, I've gone through the
draft and identified the changes that would need to be made in order to
simplfy Diameter/RADIUS translation for Disconnect and CoA messages.

This involves adding a Service-Type attribute with value "Authorize Only"
to both Disconnect/CoA messages as well as to RADIUS Access-Request
messages.  This is akin to the Diameter usage model so that translation
between the two protocols is greatly simplified.

Support for incompatible disconnect and change of authorization models
appears to represent a deployment issue for Diameter.  Given the
widespread implementation of RADIUS, if a Diameter server could not
disconnect or CoA messages, then it would be undeployable in networks that
required that capability.

A version of the specification including the changes (which would be
optional to implement) is available here:

http://www.drizzle.com/~aboba/IEEE/draft-chiba-radius-dynamic-authorization-19.txt

Comments requested.