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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.mail
Subject: Re: Neighbor optimized away
Message-ID: <1268@umcp-cs.UUCP>
Date: Wed, 30-Apr-86 01:06:43 EDT
Article-I.D.: umcp-cs.1268
Posted: Wed Apr 30 01:06:43 1986
Date-Received: Sat, 3-May-86 01:47:42 EDT
References: <4509@dartvax.UUCP>
Organization: Computer Sci. Dept, U of Maryland, College Park, MD
Lines: 34
Keywords: uucp pathalias
Summary: bad cost metrics

In article <4509@dartvax.UUCP>, steve@dartvax.UUCP (Steve Campbell) writes:

> We run a version of uumail.  It optimizes uucp paths by starting
> with the last (rightmost) host and working backwards until it finds
> a host that our pathalias database knows how to reach.

Aside: this is not really the right way to do this; it assumes that
UUCP host names are unique, which is demonstratably false.  A complete
database (not that anyone will ever assemble one) would show what
neighbors are required to turn a non-unique host name into a unique one
(normally one suffices, of course).  But back to the main point:

> Among our uucp paths is [the pair {us!Z, us!A!B!C!Z}, where] the
> pathalias "cost" of our link to Z is greater than that of path
> A!B!C!Z, so the optimizer always chooses A!B!C!Z.  This effectively
> makes our link to Z useless, which somehow doesn't seem right.

But it is right!  Either that or the cost metrics you have are wrong.
It is difficult to come up with reasonable cost values.  Perhaps what
is required is a `fuzziness' parameter for each cost: A!B!C!Z is
usually 100, but sometimes as high as 1500 and sometimes as low as 10,
with some particular statistical distribution; etc.  Then the path
resolver could toss random numbers to pick the `best' path.  It might
also (or instead) make sense to have the resolver keep a history of
past resolutions, and/or be able to scan the mail queue(s), so that it
could distribute the traffic.

(Personally, I feel that we have already reached the so-called point of
diminishing returns.  But who knows---maybe someone else will feel it
is worth the effort.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1415)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu