Subject: [NSIS] GIST: Responding Node D-Mode to C-Mode upgrade?

From: Roland Bless <[email-masked]>
Date: Tue, 31 Jul 2007 16:50:54 +0200

Hi Robert,

this is an old topic, but probably still not solved
satisfactory. Nuutti Varis, who is currently implementing
GIST at University of Helsinki, came also across this issue
again.

Problem: in case a responding node has
to send a payload larger than the MAX_MTU size, it
currently cannot upgrade the session from D-Mode
to C-mode, because it is a responding node.
See also
http://www1.ietf.org/mail-archive/web/nsis/current/msg05672.html
and your answer here:
http://www1.ietf.org/mail-archive/web/nsis/current/msg05676.html
Same applies for requiring a reliable transfer mode on the responder
side when only an unreliable transfer was considered by the querier
so far.

I could think of the following alternatives:
a) the responding node queues the data for transmission and sends
   and informative error message to the querier who can then decide
   on upgrading the session to C-mode. This has the problem that we
   need a timer on the responder side and must wait until the MA
   is established. Otherwise it will notify the application
   with a MessageStatus() call that the message could not be sent.
   Probably a part of the code could be re-used that is already
   there for initial setup of an MA. Furthermore, even smaller
   D-mode messages must enqueue behind this earlier message,
   because in order delivery for the same session is required.

b) indicate a local error condition
   via MessageStatus that the message is too large. However, reacting
   to this failure situation requires probably a similar logic that
   could have been used by the application itself _before_ calling
   the SendMessage() call.

c) see it as global policy for the NSLP as in your answer.

However, it would be good to mention the problem (and a solution)
in the draft at least.
Any other opinions?

Regards,
 Roland

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