Re: T2 Retry with Delivery Receipt

[Christopher Ferris <chris.ferris@sun.com>]

Marty,

Yes, they are "unreliable" intermediaries, the addressing
is end-to-end. Yet, when we speak of two "adjacent" ebXML
MSH nodes, that exchange messages via SMTP, the RM protocol
is between the two MSH nodes, regardless of what does or
does not happen at the lower layer.

	MSH-A->[smtp-a]->[smtp-b]->[smtp-c]->MSH-B

In the above scenario, there are NO MSH intermediary nodes.
The message traverses the SMTP routing by means of its own
layer of rules, etc. If the message does arrive at [smtp-c] and
is picked up by MSH-B and processed, MSH-B Acknowledges the
message received by sending an ebXML Acknowledgment to MSH-A
via SMTP or possibly via someother transport protocol (which
is irrelevant). None of the SMTP status codes or delivery receipts
matter to the MSH-A node. It *can* use these if it chooses,
to potentially optimize the retry (or possibly to do some
lower-level retry that is NOT part of the RM protocol per se)
but, to be perfectly clear here... it does NOT need to do so
at all.

MSH-A waits for the ebXML Acknowledgment message from MSH-B for the 
message sent. If it does not receive this before the retryInterval 
expires, then it resends the exact same message as it originally sent,
resets its timer and decrements the retries counter. It then goes back
to waiting for the ebXML Acknowledgment for the message sent.

If MSH-B receives the duplicate message, it resends the Acknowledgment
message to MSH-A (since it may have been lost in transit) but it
does NOT process the message again (it already did so the first time
it received the message).

SMTP is in this case JUST a transport mechanism that is below the
ebXML MSH level as far as the ebXML RM protocol is concerned.

Once MSH-A receives an Acknowledgment message from MSH-B, then
it *knows* that the message has been safely received, persisted
and that the responsibility for the further reliable processing
of the message has been safely transferred to MSH-B.

Yes, there are unreliable "intermediary nodes" at the SMTP level,
but that is irrelevant. There are no "unreliable" nodes at the
ebXML MSH level which is what we care about.

Cheers,

Chris

Martin W Sachs wrote:
> 
> I completely agree with your conclusion but I am curious about SMTP.  When
> I send an email, I send it to the email address that I know for the
> destination.  When I receive an email, the sender sends it to my email
> address.  Yet the header information may show that this email has travelled
> through lots of intermediary mailers.  I don't know how the routing
> mechanism works but I do know that I don't have to care about it.  I am
> doing end to end addressing.  And yes, it is below the level of ebXML but
> it is an example of unreliable intermediaries.
> 
> 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 09/14/2001 09:51:05 AM
> 
> Please respond to Dan Weinreb <dlw@exceloncorp.com>
> 
> To:   Martin W Sachs/Watson/IBM@IBMUS
> cc:   chris.ferris@sun.com, david@drummondgroup.com,
>       ebxml-msg@lists.oasis-open.org
> Subject:  Re: T2 Retry with Delivery Receipt
> 
>    Date: Fri, 14 Sep 2001 09:24:42 -0400
>    From: Martin W Sachs <mwsachs@us.ibm.com>
> 
>    Sure but it is an example of how ebxml end to end RM can work through
>    unreliable IMs.
> 
> It's an extremely important point that an SMTP mailer is not an IM.
> 
> The basic scenario involving an SMTP mailer is where the From host
> sends email to host M, running a store-and-foward mailer, and then
> host M later sends email to the To host.  This is *not* a multi-hop
> ebXML MS connection.  It is a single-hop connection.  It is *not* like
> Figure 8-2.  The From MSH calls the communcation layer saying "send
> this message to the To MSH".  If the From MSH is using RM and does not
> get an Acknowledgement, it retries, using plain vanilla hop-to-hop
> retry.  The fact that there is an SMTP mailer in there is entirely
> invisible to the MSH layer.  There is no need in this particular
> example to add end-to-end retry and a RetryCount field in addition to
> hop-by-hop retry, because it's just one hop.
> 
> -- Dan
> 
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