Re: T2, Proposed solution for ... Re: SyncReply and ReliableMessagingMethod in QualityOfServiceInfo

[Arvola Chan <arvola@tibco.com>]

David and David:

In general, the proposal looks very reasonable to me. My comments are inline
bracketed by <ac> and </ac>.

-Arvola

----- Original Message -----
From: "David Fischer" <david@drummondgroup.com>
To: "Burdett, David" <david.burdett@commerceone.com>; "ebXML CPPA (E-mail)"
<ebxml-cppa@lists.oasis-open.org>
Cc: "ebXML Messaging (E-mail)" <ebxml-msg@lists.oasis-open.org>
Sent: Friday, August 10, 2001 4:38 PM
Subject: RE: T2, Proposed solution for ... Re: SyncReply and
ReliableMessaging Method in QualityOfServiceInfo


> Very good!
>
> I have a couple of questions (no surprise) <df>in-line</df>.
>
> Regards,
>
> David Fischer
> Drummond Group.
>
> -----Original Message-----
> From: Burdett, David [mailto:david.burdett@commerceone.com]
> Sent: Friday, August 10, 2001 5:25 PM
> To: ebXML CPPA (E-mail)
> Cc: ebXML Messaging (E-mail)
> Subject: FW: T2, Proposed solution for ... Re: SyncReply and
> ReliableMessa ging Method in QualityOfServiceInfo
>
>
> I'm forwarding this email to the CPPA list as it contains some suggested
> changes for thinking about intermediaries which are relevant to the CPPA
> discussion.
>
> I'm also reposting to the ebXML Messaging list as I omitted two
attachments
> from the original post.
>
> David
>
>
> -----Original Message-----
> From: Burdett, David
> Sent: Friday, August 10, 2001 3:18 PM
> To: 'Arvola Chan'; Fischer, John
> Cc: ebXML Messaging (E-mail)
> Subject: T2, Proposed solution for ... Re: SyncReply and
> ReliableMessaging Method in QualityOfServiceInfo
>
>
> Arvola/David F
>
> I have some ideas for a few changes that might solve the problems raised
in
> this thread so the rest of this email contains:
> 1. Extracts from a number of recent emails from you both and analysis of
the
> issues/requirements they raise
> 2. Some additional further analysis of the issues to identify a few more
> requirements
> 3. A proposed solution to meeting the identified requirements which
> hopefully will solve the problem ... and who knows perhaps bring this
email
> thread to an end :-)
>
> So please let me know if:
> a) I've missed a requirement
> b) You (or anyone else) think the proposed solutiuon is wrong or could be
> improved ... but then I know you will anyway ;)
>
> Details below
>
> David
> ******************************
> EMAIL THREAD and ISSUES/REQUIREMENTS
> ====================================
>
> Arvola Chan: Thu 8/9/2001 3:28 PM
> ---------------------------------
> >>I am of the opinion that the DeliveryReceipt element should be used by
the
> ToParty MSH to inform the FromParty MSH that a reliable message has been
> received. ... It is the non-arrival of a DeliveryReceipt that requries the
> MSH to notify the application. In this case, it must rely on persistent
> information to determine the application service that must be notified.<<
>
> >>I think end to end acknowledgement is always needed to support reliable
> messaging, so it is unnecessary to explicitly set deliveryReceiptRequested
> to true, it should always be implied by deliverySemantics of
> OnceAndOnlyOnce. On the other hand, if intermediary acks are optional,
then
> ackRequested needs to be an explicit attribute at the QOS level and it
> should apply to all intermediaries.<<
>
> [DavidB]This highlights a number of issues/requirements:
> Req 1. A positive Ack sent back to the sender of a message by the ultimate
> destination is the only sure way the sender can be certain the message was
> delivered. If no Delivery Receipt is sent, then the sender cannot be so
> certain.
> Req 2. If end-to-end Delivery Receipts are always required for the sender
to
> be certain, then it would be simpler if there was a rule that
> deliverySemantics of OnceAndOnlyOnce implies a Delivery Receipt is sent.
The
> only remaining issue is whether or not the Delivery Receipt should be
> signed.
>
> David Fischer: Thu 8/9/2001 7:31 PM
> -----------------------------------
> >>Question 1 ... the end-to-end MUST be able to do RM as if it does not
know
> (which it probably doesn't) what the IM(s) are doing.  The end-to-end
> probably doesn't care if the IM(s) are doing RM at all (even though each
IM
> might care very much)<<
>
> >>On the issue of Sender time outs and retries, their are two kinds:  1) a
> timeout to the first IM and 2) a timeout getting to the end.  The first is
> easy and obvious so we don't need to discuss it.  The second is a
timeframe
> that is usually contractually guaranteed ...<<
>
> >>While the Sender/Receiver may not have any idea what path or IM
transport
> the message is taking (and they really don't need to) they must have an
idea
> about delivery times to the end.  We MUST generate some kind of an
> end-to-end Ack allowing the ends to do RM.<<
>
> >>Proposal:
> 1) We need to update section 10 with end-to-end RM (deliveryReceipt or
> something new that is similar to Acknowledgement).
> 2) We need to put in the spec somewhere that ALL MessageHeaders (including
> Via) MUST be passed to the next hop, including the end.<<
>
> >>Question 2 ... I agree that it doesn't matter if ackRequested gets
changed
> because an Ack gets sent based upon DeliverySemantics (This was my second
> solution to Question 2).  Why then do we have ackRequested?  The only way
it
> would change is if there was some kind of local CPA overriding
ackRequested.
> If RM is requested and an IM can do RM then it MUST, right?  Then why have
> this parameter?  (I see from your comments that you are considering this.)
> <<
>
> [DavidB]This highlights a number of issues/requirements:
> Req 3. The sender should not know nor care if an IM is being used and
> whether or not they are doing RM with the next IM.

<ac>
The sender application may not care if an IM is being used. The sender MSH
certainly has to know if it has to construct the Via element in order to
route
the message to an IM.

I think it may be a little simpler if the sender MSH dictates in the QOS
whether all
intermediaries use reliable messaging or not at all. If reliable messaging
is used in
every hop, then the sender MSH only needs to retry if it does not receive an
ack from
the next MSH. Once such an ack is received, it can wait for the delivery
receipt
from the to party MSH. If this is not received in time, it can simply notify
the
sender application of the delivery failure.

If none of the intermediaries use reliable messaging, and the receiver MSH
does
not return a delivery receipt in time, then it is the responsibility of the
sender MSH
to retry.

This is the approach described in the 0.93 version of the TRP spec. I think
it
is simpler because only a single set of retry related parameters is needed.
It also
make logical sense to have the sender specify the quality of service
desired, i.e.,
reliable messaging with or without intermediate acknowledgements.
</ac>

> Req 4. There are two different types of "acks" that are useful:
>   a) It's been accepted by the postal system (i.e. the next MSH has
> received, this is the Acknowledgement Message)
>   b) It's been received by the final destination (i.e. the To Party has
> received it, this is the Delivery Receipt)
> Req 5. Even if the initial Ack (i.e. Acknowledgment Message) is received
> there needs to be some method of automated retry if the Delivery Receipt
is
> not received within the expected timeframe.

<ac>
My recommendation is to retry on time out waiting for the Delivery Receipt
only
in the case of not using intermediate acknowledgements.
</ac>

> Req 6. If you a doing reliable messaging between two hops, then you do not
> need ackReqeusted as an acknowledgment must be sent if the ebXML RM
protocol
> is being sent and not needed if it isn't.
>
> David Fischer: Thu 8/9/2001 8:02 PM
> -----------------------------------
> >>I am concerned that end-to-end RM is taking a back seat to IM RM.  This
is
> the opposite of how it should be.  Most transactions will be single-hop.
> Many other cases will be single IM where the sender or receiver may not
even
> know there is an IM so it still appears to be single-hop.  The ends should
> not even have to know about the IMs.  Ends will always do automatic
retries.
> RM should work for the ends in exactly the same manner whether or not
there
> are IMs.<<
>
> [DavidB]This really just provides further support for issues/requirements
> numbered 3 and 5 above.
>
> Arvola Chan: Fri 8/10/2001 12:23 AM
> -----------------------------------
> >>Even if you have a channel that calls for the use of synchronous reply
> mode, the syncReply attribute still has to be set. In other words, it is
> still necessary to use the Via element if the syncReply attribute is
present
> only there, but this constradicts the assumption that the Via element is
> only used when intermediaries are involved.<<
>
> [DavidB]This highlights a number of issues/requirements:
> Req 7. The syncReply needs to be set at the message level whether or not
an
> intermediary is being used
> Req 8. There is a contradiction in the spec (which therefore needs to be
> removed) that the Via element is only for intermediaries when it is
actually
> also needed for non-intermediaries.
>
> DAVID BURDETT's COMMENTS
> ========================
> Before proposing a resolution to all these requirements I'd like to make a
> few comments and identify an additional couple of requirements.
>
> Firstly on Requirement 6 above (you don't need ackRequested). There could
be
> benefit in gettingan acknowledgement element back even if you are using a
> reliable messaging protocol such as MQ Series as you then have evidence
> (especially if it is signed) that the next MSH has received the message.
I'm
> not convinced though that this is a huge benefit.
>
> Secondly if we put syncReply at the message level then there is an
> additional requirement ...
> Req 9. The next recipient of a message needs to know whether or not to
> return an acknowledgement message synchronously or not.
>
> Now for the proposed solution.
>
> PROPOSED SOLUTION
> =================
> The solution dsecribed below refers to the requirements identified above
...
>
> Change 1
> --------
> Summary: Rename the Via element as "Next Actor Data" or similar
>
> Rationale: There can always be "intermediaries" in a message transfer even
> if you are going point-to-point. For example consider the two example
> message flows that I recently posted (also posted here) that cover the
> following use cases:
> 1. A genuine intermediary who is a third party that is running a MSH and
> forwards messages to the final destination.
> 2. A Party which has a MSH that acts as a "mailroom" that forwards the
> message internally using ebXML RM to another MSH that then forwards it to
> the application. The "mailroom" MSH ia an intermediary.
>
> I think we need to support both use cases. By renaming the Via element as
> "Next Actor Data" we are simply saying that the data contained within the
> element is for the Next Actor **only** and does not need to be forwarded.
> The Next Actor recreates the data as they need to. If we think of the data
> in the Via as being for the "Next Actor" then we are more closely aligned
> with SOAP. It also removes the problem of treating intermediaries as
> "something special" and allows an internal MSH to forward the message to
> another MSH without the original sender needing to know and without having
> to re-create the complete message.
>
> This change addresses Req 3 and 8.
> <df> agreed </df>
>

<ac>
I also agree.
</ac>

> Change 2
> --------
> Summary: Data in the Next Actor Data (Via) element is for the Next Actor
> only
>
> Rationale: What Change 1 means is that we must carefully review the
existing
> elements in the header and check to see whether they are needed by the
> ultimate destination/endpoint or the next actor. I think that this will
> require the following changes:
> 1. CPAId. The CPAId in the Message Header identifies parameters that apply
> "end-to-end", e.g. business process level stuff, whereas the CPAId in the
> NAD/Via element applies to the transport over a single hop, e.g. transport
> level stuff. I realise this will require changes to the CPP/A ... and
> probably more discussion.
> 2. Acknowledgment Element. This should be part of the NAD/Via element as
> acknowledgments are between two MSHs and are not propogated to the
original
> sending party.
>
> This change addresses Req 3, 4a
> <df> agreed, does the first IM send an Ack back to the From Party MSH?
does the
> To Party MSH send an ack back to the last IM MSH? The first IM would send
an Ack
> back to the From Party without being asked so the From Party needs to
understand
> this was an Ack not a DR.

<ac>
Since Acknowledgement and DeliveryReceipt are separate elements, there
should
not be any confusion.
</ac>

> The To Party would send a DR based on the presence of
> deliverySemantics=1&o1 and then if there was a Via (NAD) it would also
send an
> Ack (could be in the same message).

<ac>
If no intermediary is involved, the To Party MSH only needs to return a
DeliveryReceipt. There is no need to return an (intermediate)
Acknowledgement.
The Via element can be present even if no intermediary is involved. See Req
8
above.
</ac>

> Why isn't TraceHeaderList a sub of Via?
> Never mind -- too late. </df>
>
> Change 3
> --------
> Summary: Make the return of a Delivery Receipt required if
> deliverySemantics=OnceAndOnlyOnce
> <df> agreed </df>
>

<ac>
I also agree.
</ac>

> Change 4
> --------
> Summary: Replace deliveryReceiptRequested by deliverReceiptSigned=true or
> false(the default)
>
> Rationale: As the return of a Delivery Receipt is the only sure way that
you
> know a message was delivered suggests that it will be a simpler solution
if
> we make this always the case. Therefore we can make the return of a
delivery
> required if the deliverySemantics are OnceAndOnlyOnce. However you still
> need to know if the receipt must be signed.
>
> These changes address Reqs 1, 2, 4b
> <df> agreed  What about the requirement that
reliableMessagingMethod=ebxml?  Can
> we drop that?  What would it mean if deliverySemantics=BestEffort and
> DeliveryReceiptSigned=signed|unsigned? </df>
>

<ac>
I think it would be inconsistent to specify BestEffort delivery and yet ask
for
a delivery receipt. Perhaps the receiving MSH should return an error.
</ac>

> Change 5
> --------
> Summary: Make the return of an Acknowledgment element in a message
required
> if the ebXML RM protocol is being used

<ac>
I agree. I would also prefer to rename this as IntermediateAck, and use it
only
when intermediaries are involved.
</ac>

> Change 6
> --------
> Summary: Replace ackRequested by ackSigned=true or false(the default)
>
> Rationale: The rationale for doing this is similar to changes 3 and 4. It
> simply gives the rule that if you are doing ebXML RM then you must include
> an Acknowledgment element in the response. The response can be synchronous
> or asynchronous (see change 9 below).
> <df> agreed.  Same comments as DeliveryReceiptSigned </df>
>

<ac>
I agree. I would also prefer to rename this as IntermediateAckSigned.
</ac>

> Change 7
> --------
> Summary: Include automated retry by the original sender (From Party) if no
> Delivery Receipt is returned
> <df> agreed.  Need to be careful since the retryInterval specified in the
CPA is
> end-to-end and there is no IM retryInterval (probably need one). </df>
>

</ac>
Please see my earlier comments about Req 3. I think retry is called for only
in
case intermediate acks are not used.
</ac>

> Change 8
> --------
> Summary: Include "ResendOfMessageId" element in the Message Header
>
> Rationale: There is a need for automated retry by the original sender
(from
> party) if a Delivery Receipt is not received. However, the original sender
> cannot send the **identical** message as it will be treated as a duplicate
> and therefore ignored by any intermediate MSH that has previously received
> it. To solve this problem the from party needs to use a different
MessageId.
> However there is now a need to stop the message being treated as a
> completely new message. To solve this problem we could add a
> "ResendOfMessageId" element that identifies which message the new message
is
> a resend of. In this case even if the resend is received first and the
> original appears some time later, the ToParty will be able to recognize
that
> the message has already been processed and therefore the original should
be
> ignored. This logic needs to be included in section 10 and probably needs
a
> bit more thinking through.
>
> These changes addresses Req 5
> <df> How does the Sender know to use this?  The sender may not know there
is an
> IM.  I understand the problem, I'm just not sure this is the right
solution.  I
> think the Sender must be allowed to send the **identical** message.  A
duplicate
> at the IM is not the same as a duplicate at the To Party MSH.  The
presence of a
> duplicate at the IM should signal a problem, not necessarily stop the
message.
> Have to think about this more.  What about always including a retry
number?
> </df>
>

<ac>
This change would not be necessary if the sender MSH dictates whether
intermediate
acks are used by all intermediaries or not at all.
</ac>

> Change 9
> --------
> Summary: Include syncReply at both the Message Header and the NAD/Via
> elements
>
> The To Party needs to know whether the From Party wants the Delivery
Receipt
> and Business Payload assembled into one message.The next MSH needs to know
> whether to send back an Acknowledgment synchronously or wait for the
> Business Payload before sending it. The Delivery Receipt and Business
> Payload can be sent asynchronously and the Acknowledgment sent
synchronously
> and vice versa as they are independent of each other.
> As you can't easily cover both requirements in a single element, they need
> to be included separately in the header and in the via.
>
> This change adresses Reqs 7 and 9.
> <df> agreed.  Might have an Ack in there too.  I still like changing
> Acknowledgement to Ack.
>
> Good Plan.</df>
>

<ac>
I also agree.
</ac>

> Product Manager, xCBL, XML Standards
> Solution Strategy, Commerce One
> 4400 Rosewood Drive, Pleasanton, CA 94588, USA
> Tel/VMail: +1 (925) 520 4422; Cell: +1 (925) 216 7704
> mailto:david.burdett@commerceone.com; Web: http://www.commerceone.com
>
>
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