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Subject: Re: Guaranteed duplicate elimination vs. upper bound on delays
Marty, persistDuration and time-to-live are orthogonal. A persistDuration may need to exceed time-to-live to address messages that are received after some delay related to their delivery. persistDuration is a function of the receiver, not the sender. Cheers, Chris Martin W Sachs wrote: > > Comments below. > > Regards, > Marty > > ************************************************************************************* > > Martin W. Sachs > IBM T. J. Watson Research Center > P. O. B. 704 > Yorktown Hts, NY 10598 > 914-784-7287; IBM tie line 863-7287 > Notes address: Martin W Sachs/Watson/IBM > Internet address: mwsachs @ us.ibm.com > ************************************************************************************* > > Dan Weinreb <dlw@exceloncorp.com> on 08/15/2001 01:28:24 AM > > Please respond to "Dan Weinreb" <dlw@exceloncorp.com> > > To: Martin W Sachs/Watson/IBM@IBMUS > cc: ebxml-msg@lists.oasis-open.org > Subject: Re: Guaranteed duplicate elimination vs. upper bound on delays > > Date: Mon, 13 Aug 2001 16:38:12 -0400 > From: Martin W Sachs <mwsachs@us.ibm.com> > > As I recall, there is a time to live associated with each IP packet, > which > helps TCP manage these things. I agree that a message service time to > live > would help by killing the really long-delayed messages. > > MWS: I agree with the paragraphs above and below. But the basic idea is > the > same. Get rid of the stuff that has been hanging around too long before it > causes trouble. > > Actually I think that in real life, the time-to-live field in the IP > packet isn't really used as a measure of realtime, but as a hop count, > decremented by each router, mainly in order to get rid of looping > packages that can arise during unusual circumstances such as when > network traffic is proceeding while the routers are changing their > configurations/tables/etc. > > The story on how TCP does this, unfortunately, appears to be > complicated. See http://www.lcg.org/sock-faq/detail.php3?id=13, and > also RFC 1337 and especially the the Appendix to RFC 1185 (search for > "The scheme finally adopted for TCP combines features of both these > proposals. TCP uses three mechanisms:"). > > The key thing seems to be the TIME_WAIT state. The following > quotation is from the sock-faq, from Richard Stevens, who, as they > say, "wrote the book" on TCP (several books actually): > > The reason that the duration of the TIME_WAIT state is 2*MSL is that > the maximum amount of time a packet can wander around a network is > assumed to be MSL seconds. The factor of 2 is for the round-trip. The > recommended value for MSL is 120 seconds, but Berkeley-derived > implementations normally use 30 seconds instead. This means a > TIME_WAIT delay between 1 and 4 minutes. Solaris 2.x does indeed use > the recommended MSL of 120 seconds. > > As far as I can tell the 120 seconds is arbitrary and has nothing to > do with the IP time-to-live feature. Unfortunately for us, we are not > dealing with IP routers but potentially with store-and-forward > mailers, which might accept and store a message, and then suffer a > head crash requiring spare parts that might not arrive for weeks, > especially if the poor high-tech company is on credit hold and the MIS > guy is on vacation, and then it might come back up and finally forward > the message a month later. > > MWS: That means that if the application cares, it also needs a time to > live. That should be a parameter of the BPSS spec if it isn't already. > Including time-to-live (persist duration) helps be allowing the MSH to > clear out the junk that arrive too late for MSH duplicate detection > earlier but I'm beginning to think that if that's its > main purpose, persistDuration must be supplied by the application > > -- Dan > > ---------------------------------------------------------------- > To subscribe or unsubscribe from this elist use the subscription > manager: <http://lists.oasis-open.org/ob/adm.pl>
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