Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!intercon!amanda@intercon.uu.net
From: amanda@intercon.uu.net (Amanda Walker)
Newsgroups: comp.dcom.lans
Subject: Re: What services does X.25 provide?
Message-ID: <1444@intercon.UUCP>
Date: 11 Sep 89 22:05:43 GMT
References: <796@maxim.erbe.se> <3279@wasatch.utah.edu> <522@wet.UUCP> <3290@wasatch.utah.edu>
Sender: news@intercon.UUCP
Reply-To: amanda@intercon.uu.net (Amanda Walker)
Organization: InterCon Systems Corporation
Lines: 45

In article <3290@wasatch.utah.edu>, haas@wasatch.utah.edu (Walt Haas) writes:
> Unfortunately the Internet's definition of "reliable" isn't reliable,
> since the TCP layer gives no notice at all when the route to the remote
> host goes down.

The only layer that should care or know about routing is the layer that
actually does it (IP, in this case).  A program that uses the services of
a given level should not know what's going on in different levels.  For example,
somthing that uses TCP should not *care* if the IP level has to switch routes,
or wait for a gateway to reboot, or whatever.  Virtual circuits are good
models of wires.  They are not good models of packet delivery.  "Reliable"
in the TCP sense means that (a) if it can get there, it'll get there, (b)
it'll only get there once, and (b) you'll know it got there, even if things
happen along the way.  I'd rather have my network cope with difficulty than
to throw up it's hands and give up :-)...  This is why, in a TCP/IP environment,
X.25 is only useful as a way to route unreliable datagrams to another point.

> Bear in mind that TCP is a military protocol designed
> primarily for an environment in which a hostile enemy is shooting holes
> in the network,

Or lightning strikes, power outages, momentary failures, congestion.  These
things do happen in the real world.

> In the world of commercial applications
> that most of us work in, the environment and requirements are far different
> from the military world.

This is only true in trivial cases.  Assuming the best, especially in a data
communication environment, is a strategic mistake.  Things go wrong, even
on the best of networks.  Life is like that.  Gateways can still crash.
Backhoes can still cut through fiber optic cables.  Lightning can still strike
satellite dishes.  Squirrels can chew through phone and power lines.

> The massive inefficiencies forced by using
> military protocols for everything regardless of the environment would
> preclude TCP/IP from civilian use if the government didn't heavily subsidize
> its use.

What's so inefficient about TCP/IP in civilan use?  I mean, especially compared
to, say, ISO OSI...  It works, it's fast, it has survived the test of time.

--
Amanda Walker
amanda@intercon.uu.net    |    ...!uunet!intercon!amanda