Path: utzoo!utgpu!attcan!uunet!husc6!mailrus!ames!pasteur!ucbvax!LABS-N.BBN.COM!mckenzie
From: mckenzie@LABS-N.BBN.COM (Alex McKenzie)
Newsgroups: comp.protocols.tcp-ip
Subject: ST in gateways
Message-ID: <8809291545.AA12168@ucbvax.Berkeley.EDU>
Date: 29 Sep 88 14:46:43 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 39

In a message sent yesterday, C. Philip Wood asked Claudio Topolcic "Why
would you have to implement ST in a Gateway? Or, is IP on the way out?
Or, are we talking, implementing TOS?" Claudio is away for two weeks, so
I'll try a partial answer for him.  

ST is a protocol at the same level as IP, so a gateway can run them in
parallel; IP is not "on the way out".  

ST is a protocol which tries to provide a "guaranteed" amount of
bandwidth with low variance in delay to a user (the word is in quotes
because no guarantee is absolute); it was developed in the DARPA
Wideband Satellite network to match the characteristics of voice and
video conferencing better than IP did. ST deals not only with the
individual datagrams of a conference, but also with the "setup" when the
desired bandwidth is specified and the participants are identified.
With today's Internet topology including LANs, MANs and WANs with data
rates equal to or better than the WidebandNet, it is desirable to try to
extend the ability to participate in voice/video conferences to systems
not directly connected to WidebandNet but connected indirectly via
networks of appropriate capacity (especially LANs, today).  This
requires that ST protocol be implemented in the gateways interconnecting
the participating networks

It might be possible to implement similar functionality with TOS, but
probably not as efficiently.  The ST protocol makes use of the fact that
the datagrams of a conference are logically related and their timing is
somewhat predictable.  It allows feedback to the ST users when their
requests for bandwidth cannot be satisfied.  It provides for minimizing
the transmission of datagrams to multiple participants by carrying out
the dispersion/duplication as far down the pipe as possible.  All of
this is hard to do with stateless processing of IP, even with TOS.

Finally, ST has several years of experimental experience behind it and
is now serving as the basis for regular conferences.  Extension beyond
WidebandNet is an immediate need.  Nothing being done now will preclude
any type of TOS implementation, or even its possible use in the future
for conferencing.

Alex McKenzie