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Subject: [ebxml-cppa] Re: Sachs 10/14/2002: [ebxml-msg] Reliable Messaging
FYI
*************************************************************************************
Martin W. Sachs
IBM T. J. Watson Research Center
P. O. B. 704
Yorktown Hts, NY 10598
914-784-7287; IBM tie line 863-7287
Notes address: Martin W Sachs/Watson/IBM
Internet address: mwsachs @ us.ibm.com
*************************************************************************************
----- Forwarded by Martin W Sachs/Watson/IBM on 10/14/2002 01:21 PM -----
Martin W Sachs
To: "Monica Martin" <mmartin@certivo.net>
10/14/2002 01:21 cc: "Monica Martin" <mmartin@certivo.net>
PM From: Martin W Sachs/Watson/IBM@IBMUS
Subject: Re: Sachs 10/14/2002: [ebxml-msg] Reliable Messaging(Document link: Martin
W. Sachs)
Monica,
If we had a "BSI" specification, the reliable messaging recovery protocol
could be specified there since the reliable messaging recovery protocol can
be viewed as in the layer above the MSH. Given that we do not have a BSI
specification and the reliable messaging protocol is already in the MSG
specification, adding the additiional function to handle system failures is
best done in the MSG specification.
If by "Business Collaboration Protocol", you mean BPSS, I guess you could
consider putting the reliable messaging recovery protocol there but then
you run into the reality that use of BPSS is recommended but not required.
The reliable messaging protocol should be complete in the MSG specification
so that it can be used with whatever higher level protocols are present.
Regards,
Marty
*************************************************************************************
Martin W. Sachs
IBM T. J. Watson Research Center
P. O. B. 704
Yorktown Hts, NY 10598
914-784-7287; IBM tie line 863-7287
Notes address: Martin W Sachs/Watson/IBM
Internet address: mwsachs @ us.ibm.com
*************************************************************************************
"Monica Martin"
<mmartin@certivo. To: Martin W Sachs/Watson/IBM@IBMUS
net> cc: "Monica Martin" <mmartin@certivo.net>
Subject: Sachs 10/14/2002: [ebxml-msg] Reliable Messaging
10/14/2002 12:17
PM
Marty,
Does this happen at the application transport level (ebMS) or the higher
level business process (and possibly human-to-system)? This may be
where a discussion comes in about Business Collaboration Protocol which
could handle the state at the BSI/BSV, transaction and collaboration
levels. It is not syntax specific, and appears to lie about the
application transport of ebMS.
Thoughts?
Monica
-----Original Message-----
From: Martin W Sachs [mailto:mwsachs@us.ibm.com]
Sent: Monday, October 14, 2002 9:46 AM
To: ebxml-msg@lists.oasis-open.org
Subject: [ebxml-msg] reliable messaging
It has been pointed out to me that ebXML reliable messaging is not
reliable
under system failure. At least one person who mentioned it considers
ebXML
messaging to be broken as a result. Here is a scenario:
Party A send a message reliably to Party B.
Party B's MSH receives and persists the message.
Party B's MSH attempts to send the reliable-messaging acknowledgment but
Party B's system goes down before the acknowledgment gets on the wire.
Party A exhausts its retries and concludes that the message was not
delivered.
Party B eventually comes up and the destination application processes
the
persisted message as prescribed in the MSG specification.
Parties A and B are now out of sync with respect to that transaction and
do
not know they are out of sync. Party A believes that the transaction
failed. Party B has in fact processed the message that it received from
Party A. Reliable messaging has failed to deliver on its promise.
The solution to this problem is not trivial and the MSG team needs to
give
it a lot of thought. At a minimum, the following are needed in the
spec:
1. Both parties to the message exchange MUST persist enough state to
allow
recovery and getting back in sync. Specific state variables must be
prescribed. They are at least those variables needed to restore the
state
of the transaction and conversation after system recovery, such as the
conversation ID, CPA Id, service, action, and perhaps other parts of the
message header.
2. Timeouts and retries, as prescribed in the MSG spec, are not
sufficient
to cover system failures since the failure could last a very long time.
Instead, if the party that sent the message doesn't receive a reply in a
reasonable time, it must be able to send a status query to the other
party
and keep requesting status periodically until it receives a response.
The
status query protocol must be defined in the MSG specification. If the
appropriate state information is persisted at both ends, when party B
comes
up, it will receive and respond properly to the status query. The
timeouts
could be retained in the spec but their main use would be to signal the
"attached human" to make a phone call.
The MSG team should consider this a work item for version 3. Should the
team not wish to solve this problem, at the very least, a caveat should
be
added to the MSG specification that messaging reliability under
conditions
of system failure is outside the scope of the MSG team.
Regards,
Marty
************************************************************************
*************
Martin W. Sachs
IBM T. J. Watson Research Center
P. O. B. 704
Yorktown Hts, NY 10598
914-784-7287; IBM tie line 863-7287
Notes address: Martin W Sachs/Watson/IBM
Internet address: mwsachs @ us.ibm.com
************************************************************************
*************
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