Subject: Re: [Ips] Multi-connection sessions and ErrorRecoveryLevel=0

From: [email-masked]
Date: Sat, 17 Apr 2004 12:26:57 -0400

>- Session is in progress consisting of 2 TCP connections {C1, C2)
>- Initiator and Target have negotiated ErrorRecoveryLevel=0
>- The target detects an error on TCP connection C1.
>What is the target supposed to do?  And, for any initiator-implementers
>out there, what actions do you plan to take in the face of such an event?

I think the spec. covers what happens to the commands on the
lost connection.  But the error recovery level 0 case not spelled
out in one section.  The commands do not persist (3.2.7), and if
the initiator attempts reinstatement (maybe the target has not
noticed the connection failure yet) it must terminate the commands
immediately (5.3.4).  You also have to look at clearing effects in
appendix F1. (partial pdus are cleared etc.).

>But is there provision within the spec for the session to persist
>beyond the loss of an individual TCP connection, even though ERL=0
>eliminates the possibility for task reassignment and connection
>recovery?

By definition the session persists, but the question is for error
recovery level 0 is it useful?  I think that it could be depending
on the situation:
1.  If there were no commands in process or transit on that lost
connection then the session can definitly continue without a
problem.  The initiator can even add another connection to replace
it.
2.  Partial PDUs in transit but none in process.  The initiator
should see an error on send and must clear the partial pdu.  It
can then re-send it on another connection (assuming it has not
sent a higher cmdsn already, if so then you have a sequence gap).
3.  Commands in process by the target. The status cannot return on the
same connection. This can be handled by a task management from the
initiator.

In any case at the target you can only wait for task management
or if you detect something really bad then do session recovery. But
I don't think session recovery is automatic for a lost connection
at level 0.

I hope this helps, I am also working on multiple connection issues
with erl 0, so I would appreciate any comments.

Aaron

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