Subject: [AAA-WG]: Questions on RFC 3588

From: "Wiehe Ulrich" <[email-masked]>
Date: Fri, 30 Apr 2004 16:15:03 +0200

Dear experts,

Your help in answering the following questions with regard to RFC 3588 is
very much appreciated:

3GPP have defined a vendor-specific Diameter-Application (3GPP Cx Rel-5) for
which IANA has allocated an application-Id (167772151). Now  3GPP are in the
process of defining a new version of this application (3GPP Cx Rel-6). The
new version is an extension of the old version,i.e. nodes supporting the new
version do also support the old version. The new version does not replace the
old version, i.e. interworking between nodes supporting only the old version
and nodes supporting the old and the new version is required.

Let us assume that the difference between the old version and the new version
is that a new AVP is added to a command and this AVP has the M-bit set.

The first question is: Is it necessary to get a new application-Id allocated
by IANA for the new version, or is it possible for both versions to share the
same (already allocated) application-Id, and to achieve interoperability
between the two versions by means of the mechanism defined in RFC 3588
section 4.1 (description of the 'M' bit), i.e. the node sending the new
mandatory AVP must be prepared to receive error code 5001 (unsupported AVP)
and re-send the command in a Rel-5 compliant form?

Here are some quotes from RFC 3588 which you might want to consider when
answering the question:

-In section 1.1: "AVPs may be added arbitrarily to Diameter messages, so long
as the required AVPs are included and AVPs that are explicitly excluded are
not included." 

-In section 1.2.3:" 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."

-In section 1.2.3:"Creation of a new application should be viewed as a last
resort."  

The second question  is similar: If the difference between the old version
and the new version is that an existing mandatory AVP is removed from a
command is it then necessary to get a new application-Id allocated, or can
interoperability be achieved in the way that the node omitting the mandatory
AVP must be prepared to receive error 5005 (missing AVP) and re-send the
command in a Rel-5 compliant form?

The last question: If the difference beween the old version and the new
version is that a new command is added is it then necessary to get a new
application-Id allocated, or can interoperability be achieved in the way that
the node sending the new command must be prepared to receive the error 3001
(unsupported command)  and fall back to Rel-5?

Thank you for your help.

Ulrich Wiehe 

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