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Subject: Re: Guaranteed duplicate elimination vs. upper bound on delays


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.



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
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