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Subject: Re: [ws-rx] NEW ISSUE: semantics of "at most once" delivery assur ance

On Thu, 28 Jul 2005 13:06:50 -0700, Anish Karmarkar  
<Anish.Karmarkar@oracle.com> wrote:

> The protocol, as is defined today, is AtLeastOnce (as Chris keeps  
> reminding us), between the RMS and RMD.
> It seems to me that using this protocol for AtMostOnce is  
> wasteful/inappropriate/expensive. I.e., if AtMostOnce semantics is  
> desired why would one use WS-RM and pay for AtLeastOnce semantics (whose  
> costs can be significantly higher).
> The two sensible options that I see are either:
> 1) say that our protocol is AtLeastOnce and we don't say anything about  
> AtMostOnce at all. If someone wants to use AtLeastOnce at the protocol  
> level and implement AtMostOnce at the application level they can  
> certainly do it. We don't say that 'Unreliable' DA is supported, but  
> someone can use WS-RM to do unreliable messaging (and pay the higher  
> cost) -- although I don't know why someone would do that.

It makes the most sense to me to take this approach. Although more choice  
is usually good, it seems onerous to me to require support of AtMostOnce  
semantics on the wire. Unless I see something that proves otherwise, I  
feel we should say that our protocol is AtLeastOnce.

> or
> 2) say that AtMostOnce semantics are important in the world of reliable  
> messaging and Tom/Gil have cited use cases for it, and change our  
> protocol on the wire to accommodate this. I.e., the protocol on the wire  
> will not always be AtLeastOnce protocol. This would allow the  
> sender/receiver to pay the price for the QoS that is desired (and  
> nothing higher).
> Comments?
> -Anish
> --
> Dan Leshchiner wrote:
>> if AS makes RMS aware that AtMostOnce is used by AD/RMD, then RMS can  
>> assume that no retransmissions will be necessary and, consequently,  
>> does not need to take up its resources to make retransmissions  
>> available, right?
>>  Christopher B Ferris wrote:
>>> I think you meant AtMostOnce mode. I suppose you could do that, but  
>>> from the
>>> perspective of the RMS, it is still retransmitting until it receives  
>>> an ack.
>>> 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
>>> Dan Leshchiner <dleshc@tibco.com> wrote on 07/27/2005 06:36:24 PM:
>>>> Christopher B Ferris wrote:
>>>>> However, the protocol as specified would never be able to complete a  
>>>>> sequence
>>>>> if there are lost messages from the RMD perspective and the RMS is  
>>>>> not
>>>>> retransmitting them.
>>>> why so? as RMD, if i see a gap or AckRequested for a sequence number  
>>>> i have not received and i am operating in "at least once" mode with  
>>>> my AD,
>>>> why cant i just send an Ack? if i did so, wouldn't that enable us to  
>>>> complete the sequence?
>>>> thanks,
>>>> dan

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