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