Subject: [AAA-WG]: Re: Diameter MIP use of Application-IDs

From: Bernard Aboba <[email-masked]>
Date: Mon, 14 Jun 2004 08:15:14 -0700 (PDT)

> The only point that is not explicitly mentioned in draft-18 but that
> is explicit in Jari's text is the MUST requirement for setting the
> Application-ID to 4 even in the base commands.  However, I think this
> should be well understood by a reader who is also familiar with the
> base protocol.

RFC 3588 says that changing the Application-ID is a last resort:

"  Should a new Diameter usage scenario find itself unable to fit within
   an existing application without requiring major changes to the
   specification, it may be desirable to create a new Diameter
   application.  Major changes to an application include:

   -  Adding new AVPs to the command, which have the "M" bit set.

   -  Requiring a command that has a different number of round trips to
      satisfy a request (e.g., application foo has a command that
      requires one round trip, but new application bar has a command
      that requires two round trips to complete).

   -  Adding support for an authentication method requiring definition
      of new AVPs for use with the application.  Since a new EAP
      authentication method can be supported within Diameter without
      requiring new AVPs, addition of EAP methods does not require the
      creation of a new authentication application.

   Creation of a new application should be viewed as a last resort.  An
   implementation MAY add arbitrary non-mandatory AVPs to any command
   defined in an application, including vendor-specific AVPs without
   needing to define a new application.  Please refer to Section 11.1.1
   for details."

The AMR/AMA and HAR/HAA commands meet this criteria.

However, it wouldn't appear to me that the criteria is met for Accounting
commands, or for other commands that don't require new mandatory AVPs.

We've had this same point come up in Diameter EAP, and even in 3GPP
discussions, so it does seem to me that we need to be clear on how
Application-IDs are used in all commands.  Leaving this "implicit" can
lead to confusion.