[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [ws-rx] NEW ISSUE: semantics of "at most once" delivery assurance
Christopher B Ferris wrote: >Umit, > >I actually *do* see use cases for AtMostOnce DA observed between the RMD >and AD. It relates to >best effort with duplicate detection, really. Again, consider an endpoint >with constrained resources. >It will provide reliable delivery with ExactlyOnce semantics until or >unless the aggregate store of >unprocessed messages exceeds some threshold. > > Well if this was the grade of service I contracted for, I would feel free to just not buffer messages for retransmit, because they could get lost anyway. I do not think the current ws-rm protocol breaks if the sender does not retransmit non acked messages. The protocol, even in this at least once case, should continue to ack those messages which have been delivered, that way the sender knows and can decide to retransmit if it wishes in this "at least once" scenario. My point is, at least once, does allow different sender behaviour, in that it need not retransmit non acked messages. Tom Rutt >Would I want that level of assurance for deposits to my bank account? >Probably not. However, >I suspect that there are probably quite a few applications for which a >best effort with duplicate >detection (AtMostOnce) would be more than adequate to the task. > >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 > >"Yalcinalp, Umit" <umit.yalcinalp@sap.com> wrote on 07/25/2005 10:11:55 >PM: > > > >>It seems to me that the important use case to acknowledge as DA between >> >> >the RMD and AD is "exactly > > >>once" semantics. We are discussing what types of DAs need to be exposed >> >> >and be known by a client > > >>application, not the interaction between RMD and RMS. Therefore, it is >> >> >important to discuss what > > >>DAs need to be exposed as agreed between RMD and AD which will also >> >> >affect an application client's > > >>choice/behaviour. >> >>At most once esp. when the messages are permitted to be dropped on the >> >> >"floor" does not make sense > > >>as one would not bother with using RM. When one does not allow the >> >> >messages to be dropped but also > > >>required them tobe delivered only once, you end up with exactly once >> >> >semantics. I believe this is > > >>also Chris's point. >> >>From an application client's point of view, it is important to know that >> >> >the DA for exactly once > > >>is obeyed even if it is only as "observed" assurance. For example, one >> >> >may care that an endpoint > > >>is reliable and the RMD will deliver the messages exactly once to >> >> >accomodate a debit (or credit) > > >>message of a bank account. This type of DA may be used for choosing an >> >> >endpoint (As an example, I > > >>would not personally choose an endpoint for my bank which had >> >> >at-most-once DA for credit messages > > >>since my deposits may be gone to no man's land :-). As a matter of fact, >> >> >I would change my bank if > > >>the bank advertised reliable message delivery but could only advertise >> >> >at most once behaviour. For > > >>me, it is not reliable, period). >> >>Cheers, >> >>--umit >> >> >> >> >> >>From: Jacques Durand [mailto:JDurand@us.fujitsu.com] >>Sent: Monday, Jul 25, 2005 6:51 PM >>To: 'Christopher B Ferris'; wsrx >>Subject: RE: [ws-rx] NEW ISSUE: semantics of "at most once" delivery >> >> >assur ance > > > >>Let us wait for Ashok to clarify this (Ashok, have we put enough words >> >> >in your mouth yet :-) ? > > >>I think we agree that some aspect of the protocol would be useless for >> >> >just AtMostOnce, but I'd > > >>argue that the notion of sequence and seq number is quite important for >> >> >implementing an efficient > > >>duplicate check - so even if no Ack nor resending is needed, I'd say it >> >> >is valuable to use this > > >>part of the protocol (meaning the sequence creation and usage). >>-Jacques >>-----Original Message----- >>From: Christopher B Ferris [mailto:chrisfer@us.ibm.com] >>Sent: Monday, July 25, 2005 6:11 PM >>To: wsrx >>Subject: RE: [ws-rx] NEW ISSUE: semantics of "at most once" delivery >> >> >assur ance > > >>Jacques, >>That's not how I interpreted Ashok's note. I think he was suggesting >> >> >that > > >>it would be a waste to >>bother with ws-rm if you wanted AtMostOnce between RMS and RMD. >>Basically, I think he was saying: don't use rm for that. >>Of course, I could be completely wrong in that understanding. However, >> >> >if > > >>that's what he meant, then >>I concur. >>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 >>Jacques Durand <JDurand@us.fujitsu.com> wrote on 07/25/2005 08:35:14 PM: >> >> > > > >>>But Ashok seems to also make the point that when AtMostOnce alone is >>> >>> >>requested, then there is no >> >> >>>reason for the protocol (and for RMS / RMD) to incur the overhead of >>> >>> >>Acks and resending mechanism... >> >> >>>-JD >>>-----Original Message----- >>>From: Christopher B Ferris [mailto:chrisfer@us.ibm.com] >>>Sent: Monday, July 25, 2005 1:58 PM >>>To: ashok.malhotra@oracle.com >>>Cc: Anish Karmarkar; Doug Davis; Tom Rutt2; wsrx >>>Subject: RE: [ws-rx] NEW ISSUE: semantics of "at most once" delivery >>> >>> >>assurance >> >> >>>Ashok, >>>I gather that you don't think that the protocol itself should be used >>> >>> >to > > >>>provide an AtMostOnce >>>assurance between the RMS and RMD, and that the contract between the >>> >>> >RMD > > >>>and AD is >>>whatever the two have established between themselves (they can do >>> >>> >>whatever >> >> >>>they like). >>>I think that I pretty much agree on this point. >>>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 >>>Ashok Malhotra <ashok.malhotra@oracle.com> wrote on 07/25/2005 >>> >>> >04:30:27 > > >>>PM: >>> >>> >>>>>The WS-RM protocol itself is an AtLeastOnce protocol as >>>>>observed between the RMS and RMD. >>>>> >>>>> >>>>Let's make a note of this! If this is the case, then how is >>>> >>>> >>AtMostOnce >> >> >>>>an option as some messages may not be delivered. Sure RMD can throw >>>> >>>> > > > >>>messages >>> >>> >>>>away but then it can do whatever it wants with the messages. >>>> >>>>To my mind, AtMostOnce is not 'reliable' messaging. >>>> >>>>And if you want AtMostOnce why build the apparatus of a RMS and RMD >>>>and starting sequences etc. Why not just send messages and be done >>>> >>>> >>with >> >> >>>it. >>> >>> >>>>They may or may not get there, but that's the protocol. >>>> >>>>All the best, Ashok >>>> >>>> >>>> >>>> >>>>>-----Original Message----- >>>>>From: Christopher B Ferris [mailto:chrisfer@us.ibm.com] >>>>>Sent: Monday, July 25, 2005 1:08 PM >>>>>To: Doug Davis >>>>>Cc: Anish Karmarkar; tom@coastin.com; wsrx >>>>>Subject: Re: [ws-rx] NEW ISSUE: semantics of "at most once" >>>>>delivery assurance >>>>> >>>>>Doug is exactly right. I thought I had made this point clear >>>>>in my overview presentation at the F2F. >>>>> >>>>>The WS-RM protocol itself is an AtLeastOnce protocol as >>>>>observed between the RMS and RMD. >>>>>That means that the RMD must sucessfully receive each message >>>>>in the sequence at least once. >>>>>That means that the RMS is responsible to retransmit any >>>>>message that is unacknowledged (within the relevant intervals, >>>>> >>>>> >etc.) > > >>>>>The DA does not effect what goes on the wire. It is a >>>>>contract between the RMD and AD logical components. For >>>>>AtMostOnce, the RMD is permitted to "drop" messages (e.g. >>>>>in the case where the >>>>>RMS has a limited store for unprocessed messages and it wants >>>>>to effect a LIFO or FIFO algorithm to drop one or more of the >>>>>received (and acknowledged) messages on the floor. >>>>> >>>>>I have heard arguments that AtLeastOnce as a DA between RMD >>>>>and AD makes no sense as there is already a need for the RMD >>>>>to check for duplicates, etc. Whatever... >>>>> >>>>>I think that for the most part, the DA that will have the >>>>>most use will be ExactlyOnce, but there are valid use cases >>>>>where one could certainly envisage AtMostOnce being quite >>>>> >>>>> >relevant. > > >>>>>To Anish's point, The use and purpose of Nacks is to optimize >>>>>the protocol by taking an optimistic view of the inherent >>>>>reliability of the network. e.g. the frequency of acks could >>>>>be tuned way down and nacks used to compensate for when the >>>>>RMD knows it wants a particular message to be retransmitted. >>>>> >>>>>For the protocol to complete "correctly", a >>>>>SequenceAcknowledgement with AcknowledgementRange elements >>>>>covering the complete range of MessageNumbers for the >>>>>Sequence MUST be received by the RMS. >>>>> >>>>>A Nack is not an Ack. Just because the RMS receives a Nack >>>>>does not mean by any stretch of the imagination that the >>>>>resultant retransmission of the message will be successfully >>>>>received by the RMD. Of course the RMS is required to respond >>>>>to successive Nacks of the same message. >>>>> >>>>>In the case when the RMS does not have the message to be >>>>>retransmitted, then the Sequence must be terminated by the sender. >>>>> >>>>> > > > >>>>>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 >>>>> >>>>>Doug Davis/Raleigh/IBM@IBMUS wrote on 07/25/2005 03:09:17 PM: >>>>> >>>>> >>>>> >>>>>>Hi, >>>>>>No matter what the DA is, any unACK'd message needs to be >>>>>> >>>>>> >resent. > > >>>>>>DAs have no impact on the protocol itself. >>>>>>thanks, >>>>>>-Doug >>>>>> >>>>>> >>>>>> >>>>>> >>>>>>Anish Karmarkar <Anish.Karmarkar@oracle.com> >>>>>>07/25/2005 01:11 PM >>>>>> >>>>>>To >>>>>> >>>>>>tom@coastin.com >>>>>> >>>>>>cc >>>>>> >>>>>>wsrx <ws-rx@lists.oasis-open.org> >>>>>> >>>>>>Subject >>>>>> >>>>>>Re: [ws-rx] NEW ISSUE: semantics of "at most once" delivery >>>>>> >>>>>> >>>>>assurance >>>>> >>>>> >>>>>> >>>>>> >>>>>>Two related questions that need to be answered are: >>>>>>can a RM receiver send a NACK in case of AtMostOnce DA? If >>>>>> >>>>>> >>>>>yes, what is >>>>> >>>>> >>>>>>the RM sender supposed to do when it receives such a NACK and it >>>>>> >>>>>> > > > >>is >> >> >>>>>>never going to retransmit the message (as it has already >>>>>> >>>>>> >>>>>thrown away the >>>>> >>>>> >>>>> >>>>>>message) -- i.e. to prevent the RM receiver from NACKing >>>>>> >>>>>> >>>>>the message >>>>> >>>>> >>>>>>repeatedly, should the RM sender send a specific fault? >>>>>> >>>>>>-Anish >>>>>>-- >>>>>> >>>>>>Tom Rutt wrote: >>>>>> >>>>>> >>>>>>>*Title*: Semantics of "At most once" Delivery assurance. >>>>>>> >>>>>>>*Description*: >>>>>>>The semantics of the "at most once" delivery assurance >>>>>>> >>>>>>> >>>>>are not clear. >>>>> >>>>> >>>>>>>One interpretation is that at most once implies that the >>>>>>> >>>>>>> >>>>>sender is not >>>>> >>>>> >>>>> >>>>>>>required to retransmit mesages which are not acked. >>>>>>> >>>>>>>*Justification*: >>>>>>>It is important to clarify whether the sender must retransmit >>>>>>>unacknowledged messages when the "at most once" delivery >>>>>>> >>>>>>> >>>>>assurance is >>>>>in >>>>> >>>>> >>>>>>>use. >>>>>>> >>>>>>>*Target*: (core | soap | wsdl | policy | schema | all) >>>>>>>all >>>>>>> >>>>>>>*Type: *(design | editorial) >>>>>>>design >>>>>>> >>>>>>>*Proposal*: >>>>>>> >>>>>>>Clarify the semantics. There are at least three possible >>>>>>> >>>>>>> >>>>>semantics >>>>> >>>>> >>>>>>>associated with "at most once" >>>>>>> >>>>>>>proposal 1) at most once means that the sender will never >>>>>>> >>>>>>> >>>>>retransmit a >>>>> >>>>> >>>>> >>>>>>>message, regardless of whether it is acknolweged by the >>>>>>> >>>>>>> >>>>>destination. >>>>> >>>>> >>>>>>>Proposal 2) The sender may retransmis messages, but is >>>>>>> >>>>>>> >>>>>not required to >>>>> >>>>> >>>>> >>>>>>>to so, however the destination will not deliver duplicates >>>>>>> >>>>>>>Proposal 3) the sender must retransmit messages, however the >>>>>>> >>>>>>> >>>>>destination >>>>> >>>>> >>>>>>>may drop messages in times of resource saturation, but will >>>>>>> >>>>>>> >>never >> >> >>>>>>>deliver a duplicate. >>>>>>> >>>>>>>*Related issues*: >>>>>>>Issue 9 >>>>>>> >>>>>>> >>>>>>> >>>>> >>>>> >>>>> >>>> >>>> > > > -- ---------------------------------------------------- Tom Rutt email: tom@coastin.com; trutt@us.fujitsu.com Tel: +1 732 801 5744 Fax: +1 732 774 5133
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]