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


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.

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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