Subject: [AAA-WG]: AAA Transport Profile and Application Failure

From: [email-masked]
Date: Wed, 23 Mar 2005 14:42:48 +0100

A question has come up concerning the detection of a failed Diameter
application and the consequences for the AAA client.

RFC 3588 suggests very strongly that Diameter stacks should be implemented
in layers.  Accordingly the possibility exists that in a Proxy agent or a
server, the Diameter Base protocol handling process is functioning properly
but the application process has fallen over.  I.e. The Diameter Transport
connection is up and the watchdog commands (DWR/DWA) are being sent and
received.

In such a situation and on receipt of a Request from a AAA client, the Base
process in the Proxy (or Server) will either not send any response back to
the client at all or reply with an error and Result-Code set to
DIAMETER_UNABLE_TO_DELIVER, depending on implementation and interpretation
of RFC 3588 and RFC 3599.

The AAA client is now faced with the situation that every single Request to
a peer is failing.  Depending on the application and mode of use, an
individual Request (e.g. at the start of a Session) can failover to a
secondary peer.  However there seems to be no mechanism for the client to
detect the general failure and thereby suspend the peer and send all future
Requests directly to the alternative peer.   It seems that this situation
can occur both in a Proxy Agent and in a Server.

Have I miss-understood the mechanisms or even the architecture of a
Diameter node?  Or is this "out-of-scope" of the RFCs, possibly being
"implementation dependent"?

Best Regards

Mike Hillier

Michael Hillier
Mobile  +49 170 5454 121
[email-masked]