Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ig!arizona!jms@mis.arizona.edu
From: jms@mis.arizona.edu@arizona.edu (jms@mis.arizona.edu)
Newsgroups: comp.protocols.iso
Subject: Re: TCP/IP vs. OSI Performance
Message-ID: <9896@megaron.arizona.edu>
Date: 26 Mar 89 22:03:58 GMT
References: <529@skep2.ATT.COM> <9882@megaron.arizona.edu> <14957@bellcore.bellcore.com>
Reply-To: jms@mis.arizona.edu (Joel M. Snyder)
Organization: U of Arizona MIS Dep't
Lines: 33

Phil Karn suggests that knowing the length of an IP message ahead of
time is immaterial given that you have lots of memory to play with.
As difficult as it is to quibble with the author of a major IP implementation,
I think that it's important to point out that *the* major defect of
the TCP/IP protocol suite falls in IP---its routing (rather, lack of
thereunto) and congestion-control techniques.  Having the additional
information that a mongo huge packet is coming your way doesn't 
contribute to a nice stateless system, but it does allow you to begin
to gather the memory resources you will need early on, AND it allows
you to begin to make routing decisions based on that information.  For
example, an intelligent IP might well open a connection to a different
IP based on the MTU.

More importantly, Phil's second argument is what I consider the best
argument FOR ISO protocols.  The job of interpreting NSAP addresses
is difficult, yes, much more difficult than masking off the top two or
three bits of an RFC 791 address, but you get to address REAL end-systems
in REAL networks, not just one small Internet.  The parochial view that
a network should have no options, no room for expansion, no concept of
connection-oriented service works beautifully when you have 56K and
T1 lines floating around the place and you've got a rational addressing
authority, and you're trying to run a research network.  But the requirements
for commercial systems, and interworking between national networks, commercial
networks, and research systems, mean that expansion upon RFC 791
is really required.  Addressing and Routing in the Internet are a crock
---having an address imply a route means that IP uses up a lot of
bandwidth doing extra and unnecessary work.

I will be the last person to believe in ISO 8072/8073 (usually called TP4,
or ISO TP), but I think that 8473 contains well-reasoned and useful 
extensions to RFC 791 that can make the global Internet work.

Joel Snyder (U Arizona MIS Dep't)