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Subject: RE: T2: ackRequested attribute in Via element

Be careful.  If the goal is to reliably deliver a message from the From
party to a To party through one or more intermediaries, the only ACK that
matters is the one from the To party's MSH when that MSH has placed the
message in a persistent store. ACKs from the intermediaries, when they
receive the message, do not accomplish anything useful because the message
may be lost at or upstream of any intermediary.



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

David Fischer <david@drummondgroup.com> on 08/07/2001 01:01:45 AM

To:   "Burdett, David" <david.burdett@commerceone.com>, "'Arvola Chan'"
      <arvola@tibco.com>, ebXML Msg <ebxml-msg@lists.oasis-open.org>
cc:   mwang@tibco.com
Subject:  RE: T2: ackRequested attribute in Via element


In your example about an intermediate hop  being different, how would the
AckRequested be passed through?  Each  intermediary must recreate the Via
for the next hop based upon values it  receives.  Let's say we have 6 hops
and the middle hop (3-4) is  MQseries so it doesn't need AckRequested.  Hop
1 sends to Hop 2 with the  Via element including AckRequested=signed
(sign/unsigned doesn't matter here)  and actor=next.  Hop 2 consumes the
Via header and recreates a Via  with AckRequested=signed and actor=next
because that's what came to it and sends  to Hop 3.  Hop 3 creates a Via
with AckRequested=none and actor=next  because its hop doesn't need it and
sends to Hop 4.  How does Hop 4 know to  reset AckRequested=signed before
it sends to Hop 5?  Am I missing something  here?

I don't think this works.  I  understand the desire to have things change
on a per hop basis but I don't think  it works the way we have it now.  We
always have to leave AckRequested to  the same value even if we don't need
it for some hop -- so, it doesn't need to  go in Via.  This  goes back to
the question of what is the difference between an Ack and a
DeliveryReceipt for single-hop?  IMO the answer is Via should not be passed
to the end and DeliveryReceipt should be the end-to-end Ack.

Why do we need AckRequested at all?  All we  have to do is have
intermediate hops send back an Ack to the previous hop based  on the value
of DeliveryReceiptRequested.

1.  Get rid of AckRequested.
2.  Intermediate hop sends an Ack to the previous  hop based upon the value
of DeliveryReceiptRequested unless overridden by a  local CPA.
3.  End node sends a DeliveryReceipt, which acts  the same as an Ack, to
the sender based upon the value of  DeliveryReceiptRequested.

On the problem with unlimited messages, IMO the  observation is correct.
We should not allow an Ack to an Error.   We should also not allow an Ack
to an Ack or an Error to an Error.  We  should still allow an Error to an
Ack(we can  only allow one or the other).

-----Original Message-----
From: Burdett, David  [mailto:david.burdett@commerceone.com]
Sent: Monday, August 06, 2001  8:59 PM
To: 'Arvola Chan'; ebXML Msg
Cc:  mwang@tibco.com
Subject: RE: T2: ackRequested attribute in Via  element

See  comments inline

-----Original Message-----
From: Arvola Chan  [mailto:arvola@tibco.com]
Sent: Monday, July 30, 2001 2:08  PM
To: Burdett, David; ebXML Msg
Cc:  mwang@tibco.com
Subject: Re: T2: ackRequested attribute in Via  element


Please see my comments inline.

----- Original Message -----
From:  Burdett, David
To: 'Arvola Chan' ; ebXML Msg
Cc: mwang@tibco.com
Sent: Monday, July 30, 2001 12:11  PM
Subject: RE: T2: ackRequested  attribute in Via element


Setting the ackRequested to Signed or Unsigned is  a decision that the
designer (and/or implementer) of the business process  makes when they
design or build a business process collaboration or  business process
transaction. Factors that need to be considere include  (IMO):

   The natuure of the business process/transaction  - e.g. payments
   probably need to be secure
   The requirements of the individual trading  partners

This brings up a Messaging Service Interface  question. Does the
application (i.e., whatever software is above the MSI  layer) instruct the
MSH to send a message reliably, and/or to specify the  use of MSH level
acknowledgement, or is it the responsibility of the MSH  to infer from the
CPA and such message header elements as Service, Action,  CPAId, etc. the
quality of service that should be used for sending a  message, and then set
the QualityOfServiceInfo and Via elements  accordingly?
[David  B] I think there are several use cases which are all equally
1. The MSH looks up the  CPA
2. The Application tells the MSH to send the  data reliably
3. The MSH infers what to do by looking at the  service and action (or
other data) in the header and looking up what to do  in some type of rules

Once the CPA knows what to do it should set the  QualityOfService and Via
elements accordingly.

I have always thought that the ackRequested  attribute should be set if
reliable messaging is being used. Is it  allowable to set deliverySemantics
to OnceAndOnlyOnce and to either omit  the Via element or to include a Via
element but set ackRequested to  None?
[David  B] As currently specified I think that you have to use the Via
element if you are doing reliable messaging as you need ackRequest to  be
set even if you are doing a single hop. The reason that ackRequested is  in
the Via element is because the need for ackRequested is removed if  you are
doing multiple hops and one of the hops is using a proprietary  "reliable
messaging protocol" e.g IBM MQ Series. This really indicates  thatr the Via
element is wrongly named IMO. What are your thoughts about  changing it ...

The concept of an Acknowledgement message to  support reliable messaging
seems muddled with the concept of the  Acknowledgement element which is
primarily used to provide non-repudiation  of receipt. My colleagues at
TIBCO have pointed out to me that it seems  possible to send an
Acknowledgement message that does not carry an  Acknowledgement element,
and that only the RefToMessageId is  required.  (See lines 1816 and 1817 in
Section 10.3.3.) Can you  please confirm that this indeed is the case?
[David B] I think that what you say is  correct.

I think what would be really useful is to have a  guide that describes how
to design a business process/transaction using  ebXML Messaging. Do you
agree? If so hould it be in the 1.1 spec or  something separate.

Either way is fine with me, as long as the guide  is available around the
time the 1.1 spec is published.
[David B] Any  volunteers?

I think that if an error is dicovered then  including the ackRequested set
to true on the error message runs the risk  of a never ending series of
messages. The only use cases to consider are  where a message is being sent
reliably in which case  ...

My question was whether the error message should  be sent reliably. I was
under the impression that the CPA determines the  role played by the
receiver and the delivery channel that it will use for  receiving messages.
If the delivery channel uses a doc exchange that calls  for the use of
reliable messaging, then shouldn't the error message be  sent reliably?
[David B] Yes if the messages are being  sent synchronously.

   If the message that was in error has  ackRequested set to
   Signed/Unsigned and the error message sent in return  is lost, then the
   sender of the original message will resend it which  will cause the
   error message to be resent - see example 1  below
   If the message that was in error has  ackRequested set to None (e.g. it
   is a synchronous resposne) then  sending the error message with Ack
   Requested set to Signed/Unsigned  makes sense otherwise the sender of
   the error message will not know if  the message was delivered - see
   example 2 below

Message (with  error)(AckRequested=S/U)---------------------->
<---------------ErrorMessage (Includes  Acknowledgment element)

If the message is in error, I doubt if the  responder is obligated to
include an Acknowledgement element in the error  message, even if
AckRequested has been asked for.
[David B] Perhaps. Even  if he did not then the rules say that any errors
in an error message  are not responded to so it would not make much


Message (no  errors)(AckRequested=S/U)------------------------>
<-------Message (with error) (Includes  Acknowledgment element)

Error Message  (AckRequested=S/U)----------------------------->

<---------------Message (Includes  Acknowledgment element only)

I still  don't see why in example 1 the sender of the error message does
not set  AckRequested to S/U while in example 2 the sender of the error
message  sets AckRequested to S/U.
[David B] In example 1, suppose the ErrorMessage was  lost, then, as the
original message was sent reliably, the sender would  resend it which would
cause the Error Message to be resent. This means  that the ErrorMessage
does not need to be sent reliably as the sender of  the Error Message knows
that they will receive the original message again  if the error message is
In example 2, the Error  Message needs to be sent reliably as the sender
wants to make sure that it  was received. If it is not sent reliably then
there will be no  acknowledgement.
 Perhaps the design guide you  suggested earlier should clearly define the
error scenarios when reliable  messaging and/or AckRequested are to be

A general  rule (it's somewhere in the spec but I can't immediately find
where) says  that if you find an error in an error message then you don't
respond with  another error message and sort out the problem by some other

-----Original Message-----
From: Arvola Chan  [mailto:arvola@tibco.com]
Sent: Friday, July 27, 2001 7:40  PM
To: ebXML Msg
Cc:  mwang@tibco.com
Subject: T2: ackRequested attribute in Via  element

Section 8.7 does not clearly indicate the  circumstances under which the
ackRequested attribute should be set (to  Signed or Unsigned). Is this
governed by the ReliableMessaging and  NonRepudiation element for the
DocExchange associated with the  DeliveryChannel that is being used?

In particular, when an error is encountered  in processing a message, what
should be the strategy for setting the  ackRequested attribute in the error
message? In other words, under what  circumstances, if any, are error
messages to be sent  reliably?


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