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Subject: Re: T2, Proposed solution for ... Re: SyncReplyandReliableMessagingMethod in QualityOfServiceInfo
If I have a processing intermediary, duplicate eleimination may be critical to its operation. Consider the use case where an intermediary is a marketplace that has matched a buyer and seller, that takes a "cut" as it were of the transactions between the buyer and seller. Basically, the marketplace wants to know when the parties transact the business It would be a bad thing if it counted each retry as a distinct transaction. It must therefore apply idempotency check on the messages it processes and then forwards to the next hop in the message path. I will add that I feel that in this case, the intermediary is actually a part of the overall process, while not technically a part of the buy/sell BP that the two end-node parties share in common. However, I have heard repeatedly from the likes of DavidB and DougB that they don't consider themselves as part of the process. I think that we need to be *really* careful about treating intermediaries as mere pass-through nodes that have no part in, nor any stake in the reliable messaging aspect. Cheers, Chris David Fischer wrote: > > This sounds interesting but I don't quite understand. How can we allow > intermediates to do duplicate elimination yet also allow the ends to retry? > Wouldn't this mean the retry would get stopped midstream since some Intermediate > might think it is a duplicate? The Intermediate needs to let the From Party > retry to go through even if it is a duplicate because the problem might be > downstream of that Intermediate. > > Please explain further, > > David Fischer > Drummond Group. > > -----Original Message----- > From: Dan Weinreb [mailto:dlw@exceloncorp.com] > Sent: Friday, August 17, 2001 9:32 AM > To: david@drummondgroup.com > Cc: ebxml-msg@lists.oasis-open.org > Subject: Re: T2, Proposed solution for ... Re: SyncReply and > ReliableMessagingMethod in QualityOfServiceInfo > > Date: Fri, 17 Aug 2001 09:04:29 -0500 > From: David Fischer <david@drummondgroup.com> > > Intermediate duplicate detection precludes retries by the From Party MSH. > > If we deal with the whole issue of intermediaries by using a layered > approach, we would not have this problem. > > Consider the analogy with the Internet protocol stack. TCP (at layer > 4) is defined to be once-and-only-once. It's built on IP, which is > built on link-level (layer 2) protocols. > > The link-level protocols do not promise (in their contract to the > higher layers) any kind of retransmission of data, but some of them do > retransmission anyway (going beyond what they promised to do), because > they are in a good position to retransmit efficiently and the net > effect is to reduce the amount of retransmission that the higher > layers have to do, thus increasing net performance. > > Analogously, In the layering of ebXML MS that I and others have been > suggesting, we should have end-to-end reliable messaging, with the > IM's not *promising* to be reliable; an IM could drop a message or > duplicate a message, without breaking its contract. An IM might do > duplicate elimination anyway (going beyond what it promised to do) for > the sake of improving overall performance, but that would be entirely > invisible to the higher-layer ebXML MS protocol. And so, intermediate > duplication detection would *not* preclude retries by the From Party MSH. > > -- Dan > > ---------------------------------------------------------------- > To subscribe or unsubscribe from this elist use the subscription > manager: <http://lists.oasis-open.org/ob/adm.pl>
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