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Subject: Formal proposal for issue i020


All,

Here's a formal proposed resolution to issue i020 [1].

Rationale: 

The Delivery Assurance semantic applies to the "contract" between the 
logical RMD and AD,
and the RMS and AS roles. It does not apply to the protocol as seen "on 
the wire". 

For example, if the InOrder DA were to be manifested on the wire, it would 
mean that the RMS 
could transmit but a single message at a time. It must await receipt of a 
SequenceAcknowledgement 
from the RMD acknowledging  receipt of that transmitted message -- 
retransmitting that same message 
ad nauseum until such time as it has been acknowledged before proceeding 
to attempt transmission of the next
in-order message in the sequence. That would be pathetic. That was clearly 
not the intent of the 
specification authors.

The same applies to the AtMostOnce and ExactlyOnce DA. It is manifested 
between
the RMD and AD, and/or between the RMS and AS roles, not between the RMS 
and RMD.

The protocol itself is described as an "AtLeastOnce" protocol as 
manifested on the wire,
meaning that each message MUST be transmitted at least once, and that each 
message
MUST be acknowledged or retransmitted until such time as it has been 
acknowledged,
or the Sequence is prematurely terminated. However, the DA does not apply 
to the protocol.
Possibly, that is where the confusion lies. 

An RMD would effect an AtLeastOnce DA by passing received messages to the 
AD, possibly
without bothering to perform duplicate detection.

Proposed change/clarification:

At line 162 of the WS-ReliableMessaging spec, delete the following 
paragraph:

WS-ReliableMessaging provides an interoperable protocol that a Reliable 
Messaging
(RM) Source and Reliable Messaging (RM) Destination use to provide 
Application
Source and Destination a guarantee that a message that is sent will be 
delivered.
The guarantee is specified as a delivery assurance. The protocol supports 
the
endpoints in providing these delivery assurances. It is the responsibility 
of the RM
Source and RM Destination to fulfill the delivery assurances, or raise an 
error. The
protocol defined here allows endpoints to meet this guarantee for the 
delivery
assurances defined below.

and replace it with the following text:

The WS-ReliableMessaging specification defines an interoperable protocol
that enables a Reliable Messaging (RM) Source and Reliable Messaging (RM) 
Destination to ensure that each message transmitted by the RM Source is 
successfully received by an RM Destination, or barring successful receipt,
that an RM Source can, except in the most extreem circumstances, 
accurately 
determine the disposition of each message transmitted as perceived by the 
RM Destination, so as to resolve any in-doubt status.

The protocol allows the RM Source and RM Destination to provide their
respective Application Source and Application Destination a guarantee that 
a message 
that is sent by an Application Source will be delivered to the Application 
Destination. 
This guarantee is specified as a delivery assurance. It is the 
responsibility of the RM 
Source and RM Destination to fulfill the delivery assurances on behalf of 
their respective 
Application counterparts, or raise an error. The protocol defined here 
allows endpoints 
to meet this guarantee for the delivery assurances defined below. However, 
the means 
by which these delivery assurances are manifested by either the RM Source 
or RM 
Destination roles is an implementation concern, and is out of scope of 
this specification.

[1] 
http://www.oasis-open.org/committees/download.php/14329/ReliableMessagin#i020

Cheers,

Christopher Ferris
STSM, Emerging e-business Industry Architecture
email: chrisfer@us.ibm.com
blog: http://webpages.charter.net/chrisfer/blog.html
phone: +1 508 377 9295


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