mckenzie@LABS-N.BBN.COM (Alex McKenzie) (09/29/88)
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
CERF@A.ISI.EDU (10/09/88)
For Dave Cheriton and Alex McKenzie: 1. ST was an experiment in real-time communication on the Internet. The ST protocol, which operates at the level of IP (adjacent to it), had special features to support multicasting for voice conferencing, for instance. 2. It seems to me that the more useful debate would be whether ST or Muilticast or perhaps something along the VMTP lines is the more suitable for carrying out the kinds of explorations that Claudio wants to pursue. ST has a lot of features that emerged from pracitcal voice conferencing experiments which included long-delay satellite channels as well as the terrestrial Internet and, if memory serves, at least one packet radio network. 3. Yes, Alex, you can claim to be one of the IP and TCP developers - it was and continues to be an effort engaging the ideas and skills of many people. Vint