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From: rpw3@amdcad.AMD.COM (Rob Warnock)
Newsgroups: comp.os.research
Subject: Re: Ethernet: modsim article
Message-ID: <3896@sdcsvax.UCSD.EDU>
Date: Wed, 16-Sep-87 20:31:29 EDT
Article-I.D.: sdcsvax.3896
Posted: Wed Sep 16 20:31:29 1987
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In article <3819@sdcsvax.UCSD.EDU> pom@under.s1.gov (Peter) writes:
+---------------
| Anyway, all those with first name in [a...k] should now post a statement of
| their interest [ LANs, VANs, ...???  ??? ]
+---------------

Hmmm.... obviously an attempt to get us to use a version of the "Urn" algorithm,
often said to be near-optimal under mixed loads. Unfortunately, Urn algorithms
require universal acceptance of the rules, which I seem to have just violated...

;-}    ;-}

Fortunately, except for considerations of disk space, USENET is not a contention
protocol, but queued (assuming "inews" locks work correctly!)...


In a more serious vein, Urn algorithms *do* require universal knowledge of
the "state" of the algorithm (in this case, the state is that we are offering
permission to transmit only to "[a-k]*"), and for this reason have some
difficulty in cases such as packet radio when the packet loss rate is high.
You then have to have various heuristics to "guess" at the global state of
the algorithm, so you don't speak out of turn.


Rob Warnock
Systems Architecture Consultant

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