RE: T2, Proposed solution for ... Re: SyncReply andReliableMessagingMethod in QualityOfServiceInfo

[David Fischer <david@drummondgroup.com>]

Arvola,

<df> comments inline </df>

David Fischer
Drummond Group.
-----Original Message-----
From: Arvola Chan [mailto:arvola@tibco.com]
Sent: Tuesday, August 14, 2001 10:35 AM
To: HUGHESJIM (HP-Cupertinoex1); ebXML Messaging (E-mail)
Subject: Re: T2, Proposed solution for ... Re: SyncReply and
ReliableMessagingMethod in QualityOfServiceInfo


My opinion is that the current spec is so broken that extensive
changes may be necessary to get end to end reliable messaging
over multiple hops to work properly. I agree with you and that
intermediate Acks used by the intermediaries are the likely source
of the problem.
<df> agreed </df>

If we stipulate that only the sending MSH and the receiving MSH
adopt the reliable messaging behavior, I believe end to end reliable
messaging will work regardless of whether intermediaries are
present. However, this may make reliable messaging not very
useful for certain use cases, e.g., where the sending MSH does
not have a permanent Internet presence.

<df>  This is not all that hard if we keep the present structure of
DeliveryReceipt as the end-to-end Ack and the Acknowledgement element as the IM
hop Ack.  This is already in the spec and nothing about these elements needs to
be changed.  We only need to specify in section 10 that if the To Party MSH gets
a DeliverySemantics=1&o1 then send a DeliveryReceipt to the From Party MSH
(along with ...).

Unfortunately, this does not deal with the duplicate problem.  If I (the From
Party MSH) don't get a DR back, then I will retry (Retries and RetryInterval are
end-to-end parameters, not hop-to-hop).  I don't want any IMs rejecting my retry
due to duplicates.  We can fix this by either:
	1) telling the IMs not to worry about duplicates or
	2) add a RetryCount attribute and change the way
		IMs handle duplicates.

The way we handle duplicates now is definitely broke.  </df>

I now realize there is a problem in my previous proposal to have
the sending MSH stop retrying once it gets an Ack from the next
intermediary, and then wait for the DeliveryReceipt from the
receiving MSH. Unless the DeliveryReceipt is sent reliably, it
may get lost, so the sending MSH may falsely notify the sending
application that reliable messaging has failed. If the DeliveryReceipt
is sent reliably, then it may require end to end acknowledgement
from the sending MSH, possibly triggering an infinite chain of
DeliveryReceipt messages. (A possible workaround may be to
require that if a DeliveryReceipt is sent reliably and on its own,
then it must not request for DeliveryReceipt.)

<df> agreed -- no DR for a DR and no Ack for an Ack and no Error on an Error.
We can get carried away with RM if we start sending Acknowledgements or DR
reliably.  We also have to pick either Ack on Error or Error on Ack but not
both.  I think I prefer Error on Ack... I'm not sure?
</df>

-Arvola

-----Original Message-----
From: HUGHES,JIM (HP-Cupertino,ex1) <jim_hughes@hp.com>
To: ebXML Messaging (E-mail) <ebxml-msg@lists.oasis-open.org>
Date: Monday, August 13, 2001 7:17 PM
Subject: RE: T2, Proposed solution for ... Re: SyncReply and ReliableMessa
gingMethod in QualityOfServiceInfo


>Question: Does "reliable messaging" mean that the initial MSH (and maybe
>intermediate node MSHs) needs to consider this as a quality request and, if
>possible, pick the "most" reliable transport available? Or, is this just a
>protocol for the receiving MSH to send a confirming ACK back to the sending
>MSH?
>
>I think it's the latter, and thus there is no directive for intermediate
>node links to use the RM protocol to confirm among themselves that this
>message got through. From their perspective, the overall MSH Ack looks like
>a higher level function to them... and, in fact, it seems to me that having
>the intermediate links try to use their own version of RM between their
>endpoints really complicates the picture and maybe they should be
prohibited
>from trying to use RM since they aren't the start/end-points for the
overall
>message... IMO.
>
>jim
>
>
>
>> -----Original Message-----
>> From: Arvola Chan [mailto:arvola@tibco.com]
>> Sent: Sunday, August 12, 2001 9:30 PM
>> To: David Fischer; Burdett David
>> Cc: ebXML Messaging (E-mail)
>> Subject: Re: T2, Proposed solution for ... Re: SyncReply and
>> ReliableMessaging Method in QualityOfServiceInfo
>>
>>
>> David:
>>
>> My comments are bracketed by <ac> and </ac>.
>>
>> Cheers,
>> -Arvola
>>
>> ----- Original Message -----
>> From: "David Fischer" <david@drummondgroup.com>
>> To: "Arvola Chan" <arvola@tibco.com>; "Burdett David"
>> <david.burdett@commerceone.com>
>> Cc: "ebXML Messaging (E-mail)" <ebxml-msg@lists.oasis-open.org>
>> Sent: Sunday, August 12, 2001 2:33 PM
>> Subject: RE: T2, Proposed solution for ... Re: SyncReply and
>> ReliableMessaging Method in QualityOfServiceInfo
>>
>>
>> > Arvola,
>> >
>> > What if I am sending to you and you are using an IM for
>> some reason, e.g.
>> no
>> > persistent connection?  I might not even know and since I have no
>> agreement with
>> > that IM (my agreement is only with you), I cannot be responsible for
>> putting the
>> > CPAid in the Via -- there is no CPAid.  What I can do is
>> fill in the Via
>> fields
>> > as much as I am able in case there is an IM I am not aware
>> of.  This, IMO
>> will
>> > be a very common use case.
>> >
>> > This exact same situation would arise if you used multiple
>> MSHs where one
>> was a
>> > mailroom.
>> >
>>
>> <ac>
>> I must admit that your use case is a very valid one and I
>> have not made
>> provision for
>> it.
>>
>> Come to think of it, when I suggested that the sender MSH
>> should dictate if
>> all intermediaries
>> should use reliable message or not at all, it is not strictly
>> necessary for
>> the sender MSH to
>> know that intermediaries are involved, all it is choosing is between
>> reliable message with
>> intermediate Acks vs reliable messaging without intermediate Acks.
>>
>> As you have indicated earlier, "Even though the ends don't
>> need to know
>> about the IMs,
>>  it is critical that the IMs realize their role." There, the
>> IMs should be
>> able to respect the
>> directive from the sender MSH to use intermediate Acks or not.
>> </ac>
>>
>> > You are correct, I need to be more clear.  I believe the
>> sender MSH would
>> > construct the Via.  This Via would pass to the first IM MSH
>> who would
>> construct
>> > a new Via (possibly very similar to the original) and pass
>> this new Via to
>> the
>> > next hop's MSH.
>> >
>> > NEW PROBLEM WITH MULTI-HOP?
>> > This brings up a good point.  I (the From Party MSH) know
>> how to send to
>> you
>> > (the To Party MSH) because I can look up your connection
>> info in the CPA
>> > Database based upon a CPAid and a ChannelID.  This info
>> might not reside
>> in the
>> > To PartyID element.  If my message goes through an IM, how
>> does the IM
>> know
>> > where to send?  I don't send to you, I send to my IM.  If I
>> am using an
>> IM, does
>> > that mean any time I make an entry in my database I also
>> have to duplicate
>> that
>> > info to my IM (and they to each of their IMs etc.)?  This
>> would not be
>> > acceptable.  Maybe this connection info MUST reside in the
>> To PartyID?
>> This
>> > would not be a problem for single-hop.  Maybe the Receiver
>> connection info
>> needs
>> > to be put in the Via?
>> >
>>
>> <ac>
>> I agree with you this is a problem. The intermediary needs to
>> be configured
>> with the
>> Endpoint and various characteristics for the To Party (or the
>> Endpoint for
>> yet another
>> intermediary who can route messages to the To Party directly
>> or indirectly
>> and its
>> characteristics). My understanding is that CPPs and CPAs
>> currently deal only
>> with
>> the point to point case. Therefore, there is no automated way
>> to configure
>> intermediaries
>> using CPAs. This is something the CPP/A TC will have to
>> address in its 2.0
>> spec.
>> </ac>
>>
>> > Regards,
>> >
>> > David Fischer
>> > Drummond Group.
>> >
>
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