Subject: [Dime] congestion of intermediaries

From: "Tolga Asveren" <[email-masked]>
Date: Wed, 5 Apr 2006 15:53:20 -0400

RFC3588 7.1.3 states:
  DIAMETER_TOO_BUSY                  3004
      When returned, a Diameter node SHOULD attempt to send the message
      to an alternate peer.  This error MUST only be used when a
      specific server is requested, and it cannot provide the requested
      service.

Based on that description, I have the impression that this error code is to
be returned only by a server.

Diameter intermediary nodes, e.g. relay agents,  may get congested as well
and it could be a good idea to convey that information back to the clients
so that they pick another relay agent if possible, when routing requests.

With the current mechanisms, we probably need to rely on the congestion
getting propogated back to the client through TCP/SCTP or on watchdog
failure. IMO, this is not a very nice way of dealing with this situation,
because it may take a long time till the sender of request is aware of the
congestion and during that time a lot of requests may be already sent to the
congested node.

It could be an idea to convey congestion of intermediaries with a new error
code, something like DIAM_CONGESTED. DIAMETER_TOO_BUSY still can be used for
server congestions, where a change on Destination-Host AVP is necessary,
i.e. it should be consumed by the client, whereas DIAMETER_CONGESTED is to
be consumed hop-by-hop, i.e. by the immediate neighbor.

     Thanks,
     Tolga

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