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Subject: Re: T2 Retry with Delivery Receipt
Some responses below.
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
*************************************************************************************
Christopher Ferris <chris.ferris@sun.com> on 09/14/2001 03:00:01 PM
To: David Fischer <david@drummondgroup.com>
cc: Martin W Sachs/Watson/IBM@IBMUS, Dan Weinreb <dlw@exceloncorp.com>,
ebxml-msg@lists.oasis-open.org
Subject: Re: T2 Retry with Delivery Receipt
David,
In this case, where the MSH doesn't support ebXML RM protocol,
you cannot send a message with OnceAndOnlyOnce semantics. It
MUST send back an error "Not Supported".
MWS: Which MSH do you refer to here? The first IM or the destination
endpoint? Clearly if either the first IM or the destination doesn't support
RM but does support ebXML-MS, it must send back "not supported". If the
node that receives the message doesn't understand ebXML at all, it can't
send anything back and isn't an MSH at all. This may be obvious but that
isn't clear from some of the postings.
My point is that the RM protocol is hop-to-hop and the end-to-end
semantics are achieved by having each hop be reliable (whether
using ebXML RM or something else).
MWS: Yes, but the ebXML or ebXML-RM protocol terminates at the last point
at which there is an ebXML MSH (should be obvious also).
Think of it this way:
(routing app)
| |
A[eb] <-> [eb]B B[MQ] <-> [MQ]C
In this case, the B intermediary is reliable and supports
both ebXML RM *and* MQ series. Whether these are separate
instances or the same instance with multiple capabilities
is irrelevant. It may be distributed for that matter. The
routing app needs to be reliable as well (just as any other
app) because it should ONLY mark the message as having been
processed if it has successfully processed it.
MWS: In this case, the ebXML-MS protocol terminates at the left side of B
and B's left side is the From MSH by definition. From an ebXML viewpoint,
B and everything to the right of it are part of the system above the B MSH.
The B-C link is no more part of the ebXML protocol than is an SMTP
intermediate node.
We can be more explicit regarding what responsibilities are
at an intermediary node here, but IMHO, there really is no
difference here between a routing "application" and an endpoint
business "application" in that the MSH has a responsibility to
ensure that the "application" processes the message.
MWS: I agree with this but we must state explicitly at a minimum that
intermediate nodes must store and forward reliably.
The B node above could all be a single piece of software,
operating as a routing intermediary (which would certainly make
it more robust), but we have nothing to say on the matter
as far as our specification is concerned.
MWS: Indeed. We also have nothing to say about C or the link between B
and C.
I don't think that we need to address the situation where two
adjacent nodes don't support the same RM protocol. That would
be (IMHO) no different that an SMTP node trying to foist the SMTP
protocol on an HTTP server. They speak different protocols
and can never interact directly without some manner of gateway.
MWS: True. That situation is basically impossible.
Cheers,
Chris
David Fischer wrote:
>
> Chris,
>
> What do you mean by unreliable? I will agree there is no unreliable IM
but
> there can be an IM which does not support ebXML RM (e.g. uses MQSeries
instead).
> This is the whole point of the reliableMessageMethod parameter.
>
> David Fischer
> Drummond Group.
>
> -----Original Message-----
> From: Christopher Ferris [mailto:chris.ferris@sun.com]
> Sent: Friday, September 14, 2001 1:13 PM
> To: Martin W Sachs
> Cc: Dan Weinreb; david@drummondgroup.com; ebxml-msg@lists.oasis-open.org
> Subject: Re: T2 Retry with Delivery Receipt
>
> Marty,
>
> The SMTP "intermediaries" are not ebXML MSH intermediaries
> and thus there is no analogy at all.
>
> The whole point I make is that there isn't an unreliable
> ebXML MSH intermediary involved when OnceAndOnlyOnce is
> in play for a message.
>
> Cheers,
>
> Chris
>
> Martin W Sachs wrote:
> >
> > Sure but it is an example of how ebxml end to end RM can work through
> > unreliable IMs.
> >
> >
>
********************************************************************************
> *****
> >
> > 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
> >
>
********************************************************************************
> *****
> >
> > Christopher Ferris <chris.ferris@sun.com> on 09/13/2001 01:40:58 PM
> >
> > To: Martin W Sachs/Watson/IBM@IBMUS
> > cc: Dan Weinreb <dlw@exceloncorp.com>, david@drummondgroup.com,
> > ebxml-msg@lists.oasis-open.org
> > Subject: Re: T2 Retry with Delivery Receipt
> >
> > Marty,
> >
> > AN SMTP node is NOT an MSH node. It is not part of the equation.
> > The MSH nodes that are communication via SMTP are the ones that
> > adopt the RM protocol of retries in the absence of an Acknowledgment.
> > The SMTP nodes are incidental.
> >
> > Cheers,
> >
> > Chris
> >
> > Martin W Sachs wrote:
> > >
> > > Re: "I think David's position is that we can't do that, because
there
> > are
> > > hosts/entities out there that (a) must participate as ebXML MS IM's,
> > > and (b) that are unreliable. The question is whether there's a use
> > > case demonstrating this."
> > >
> > > There is one major use case, which is SMTP. SMTP intermediate nodes
are
> > > notoriously unreliable and only acknowledge to the previous node so a
> > > sender has no idea whether the message got to its destination. ebXML
on
> > > top of SMTP is one of the major reasons for having ebXML reliable
> > messaging
> > > and only end to end reliable messaging helps with SMTP. I don't know
if
> > > there is a use case for ebXML unreliable intermediaries but if there
is,
> > > end to end RM is the answer.
> > >
> > > 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
> > >
> >
>
********************************************************************************
> *****
> >
> > >
> > > Dan Weinreb <dlw@exceloncorp.com> on 09/13/2001 12:55:02 PM
> > >
> > > Please respond to Dan Weinreb <dlw@exceloncorp.com>
> > >
> > > To: chris.ferris@sun.com
> > > cc: david@drummondgroup.com, ebxml-msg@lists.oasis-open.org
> > > Subject: Re: T2 Retry with Delivery Receipt
> > >
> > > Date: Thu, 13 Sep 2001 11:48:33 -0400
> > > From: Christopher Ferris <chris.ferris@sun.com>
> > >
> > > > The only problem is that the addition of multi-hop interferes
with
> > > end-to-end
> > > > retries (duplicates) which, as we have seen, is a fundamental
> > > functional
> > > > requirement under all circumstances when a Delivery Receipt is
> > > requested but not
> > > > received.
> > >
> > > You're asking for retries on top of retries. What happens when the
> > > end-to-end
> > > retries are exhausted and there is still no delivery receipt? Do
we
> > add
> > > retries
> > > of retries of retries? What happens when they fail? Do we add yet
> > > another layer?
> > >
> > > What David is asking for is perfectly sensible *if* you your failure
> > > model states that IM's are unreliable, e.g. that an IM might accept a
> > > message, and then silently forget it. In that case, the end-to-end
> > > retries exist for a specific purpose: to harden the system against
the
> > > possibility of flaky IM's. There would be no need to add another
> > > layer unless there is some additional, distinct failure mode to be
> > > taken care of.
> > >
> > > Why not focus on what you perceive as an omission in the spec,
that an
> > > intermediary
> > > has certain obligations w/r/t reliable delivery. Let's address
that by
> > > adding
> > > text that fully sets out what the responsibilities of an
intermediary
> > > are
> > > not only w/r/t RM but w/r/t routing and any other oddities of an
> > > intermediaries
> > > role that is clearly distinct from that of an endpoint.
> > >
> > > I think David's position is that we can't do that, because there are
> > > hosts/entities out there that (a) must participate as ebXML MS IM's,
> > > and (b) that are unreliable. The question is whether there's a use
> > > case demonstrating this.
> > >
> > > I'd like to focus on the specific use case that you cited in the
call,
> > > where
> > > an MSH uses an EDI/INT gateway. Is there an ebXML MSH at the To
Party
> > or
> > > do they
> > > simply have an EDI/INT server?
> > >
> > > MSHA -> IMSHGW -> EDI/INTGW -> EDI/INTB
> > >
> > > In this case, how does the ebXML delivery receipt get generated?
IMO,
> > > the
> > > EDI/INT Gateway has a responsibility to ensure that the message is
> > > safely
> > > delivered. How it does this is not the perview of our
specification.
> > > However,
> > > that doesn't obviate the responsibility that the gateway
intermediary
> > > node
> > > assumes.
> > >
> > > I'd call this a protocol-translating gateway, not an ebXML MS IM at
> > > all. I agree that the gateway has to make sure that the message is
> > > truly delivered, and then the gateway generates the DR. It's the
> > > job of the protcol-translating gateway to create the illusion that
> > > the far end is really running ebXML MS.
> > >
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