Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ulysses.UUCP
Path: utzoo!decvax!ucbvax!ulysses!smb
From: smb@ulysses.UUCP (Steven Bellovin)
Newsgroups: net.news.config
Subject: Re: Abuse of ``DIRECT'' in Usenet maps
Message-ID: <1004@ulysses.UUCP>
Date: Wed, 10-Jul-85 19:12:40 EDT
Article-I.D.: ulysses.1004
Posted: Wed Jul 10 19:12:40 1985
Date-Received: Thu, 11-Jul-85 00:46:46 EDT
References: <1738@amdahl.UUCP> <313@phri.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 49

> gam@amdahl (Gordon A. Moffett) says:
> > [...] using the ``DIRECT'' cost value [...] not really DIRECT (or
> > DEDICATED) lines, but just ``very good'' DEMAND connections.
> 
> 	I take this to mean that other people are just as confused as I
> am about what the various costs mean.  To quote the pathalias man page:
> 
>           DIRECT    200       (local call)
>           DEMAND    300       (normal call)
>           HOURLY    500       (hourly poll)
>           EVENING   1800      (time restricted call)
>           DAILY     5000      (daily poll)
> 
> 	Can somebody who *really* knows what these are supposed to mean
> (i.e. one of the implementors) give some examples of situations that
> fall into the various catagories.

Back when I wrote pathalias, DIRECT was intended to refer to a direct cable
between the tty port on machine A that was connected to a tty port on machine B,
where machine B was running a getty.  That is, unless the target machine was
down or someone was cu'd over this direct wire, the connection should *always*
succeed.  I rated this as better than demand-dialed, which could fail if the
autodialer was busy, all ports on the target machine were busy, the phone
system was in some strange state, etc.  Given the rather strange phone
system in Chapel Hill at the time (a long story I'll tell some other time)
and the even stranger autodialer we were using (an even longer story I
probably won't tell), plus the fact that one of our primary correspondent
machines had only one dial-in line, all of these constraints were very real.
So that's the official word on what DIRECT meant *then* -- Peter's probably
right about using it for local calls today, though my original intention was
to use something like DEMAND+3*HIGH or some such.

I also agree with Peter that pathalias has never had a clearly-defined
goal it was optimizing towards.  The reason is quite simple:  no two people
could agree.  I decided that the primary goal was to get mail through
quickly and reliably, which in turn meant using observed frequencies of
calling and reliability as the best indicator of (a) the willingness of
someone to pay for forwarding mail and news; and (b) the willingness and
ability of the system administrator to hold uucp's hand(sic) enough.  I
made up the initial numbers by defining an important subnet that I knew
well (North Carolina plus major backbone sites plus a few hanging off of
them), and playing with the values till I got paths that matched what I
felt was optimal (given the definition cited above).  The net is far larger
now, with greater fanout but more sensitivity towards costs; my numbers
may no longer be optimal, but I do suggest caution in adjusting them -- the
output is very sensitive to minor perturbations in costs.


		--Steve Bellovin