Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site wucs.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!wucs!jst From: jst@wucs.UUCP (Jon Turner) Newsgroups: net.dcom Subject: General Purpose Communications Networks Message-ID: <1177@wucs.UUCP> Date: Sat, 21-Sep-85 12:43:50 EDT Article-I.D.: wucs.1177 Posted: Sat Sep 21 12:43:50 1985 Date-Received: Sun, 22-Sep-85 06:26:57 EDT Organization: Washington U. in St. Louis, CS Dept. Lines: 92 Keywords: communications, packet switching I've been interested for sometime in communications networks that are designed to handle a wide range of different applications and would like to start a discussion on this topic. I'm interested primarily in large public networks rather than local nets. Current networks tend to have a very strong application orientation --telephone networks and CATV networks exemplify this statement. Because the application is embedded so deeply in the network it's very difficult to adapt these networks to other purposes. Data communications networks are much more flexible, but the current crop has a fairly limited performance range which makes them unsuitable for many applications. Currently, we handle diverse communications needs by implementing multiple application-oriented networks. I feel that this approach stifles the development of new applications, because if we can't hack an existing network to do what we want (which is often the case) our only alternative is to implement yet another network. I think this approach is rapidly becoming unworkable--it's time to start thinking about networks that separate applications from communication in a way that makes it easy to develop new application. Such networks must (1) provide a rich set of generally useful communications capabilities and (2) do so at the highest possible performance level. My own work in this area started in 1981 when I was at Bell Labs. I worked with a group of people on what was called the Fast Packet Network project, which had as its goal the development of a high performance packet switching system suitable for both voice and data communication on a large scale. We designed a system using 1.5 Mbs links with fast hardware protocol processors. The switching was handled by a large binary routing network. We designed packet switches large enough to carry the traffic of a typical toll telephone switch and cost-competitive with circuit switching. Packet switching was chosen for two reasons (1) transmission economies and (2) the flexibility that it offers. The second reason is in my opinion the important one. Packet switching allows one to provide connections of arbitrary bandwidth which is difficult to do with circuit switching. I left Bell Labs about two years ago and am no longer up-to-date with the work on FPN although I understand it is continuing. Early this year I started looking into ways of extending the earlier work in order to handle higher speed applications such as video. It turns out that the speed-up required for video is not hard to obtain. Using a combination of techniques it's possible to build packet switching systems capable of handling 100 Mbs fiber optic communications links. Custom protocol processors can be implemented on two chips using 1 micron CMOS. The switching fabric becomes somewhat more complex, but the overall system complexity is still dominated by the protocol processors. The more interesting extension required by applications such as video is the need for multi-point connections. We want to be able to set up a connection that can be used to distribute a commercial television signal to possibly millions of receivers. The idea is that someone establishes a broadcast source and then other users send messages to the network asking to connect to that source. The network then hooks them into the connection at the nearest point. The switching systems take care of replicating the signal as needed. The connection induces a tree in the network spanning all the participating endpoints. The bandwidth of the source can be any speed from a few bits per second to 100 Mbs. We can generalize the simple broadcast connections to handle other applications such as teleconferencing. In this sort of application we have a multi-way broadcast or more appropriately, a broadcast in which the role of the broadcast source is passed back and forth among the different endpoints. Although we've yet to build a prototype, we've studied the problem in enough detail to be convinced that it can be practical (I'll be happy to send a paper to anyone who's interested). There are however a lot of research issues that we've only begun to address. For starters is the question of how one manages multi-point connections that can potentially contain any number of endpoints. We need efficient distributed algorithms that can establish and manage such connections using only local information. Routing is another interesting problem. In point-to-point networks, this can be treated as least-cost path problem. In a mulit-point network, we need to find the least-cost tree connecting a given set of endpoints. This is known in combinatorial optimization circles as the Steiner tree problem and is NP-complete. Congestion control is another issue that takes on added dimensions in multi-point networks. Well, this is already too long, so I'll stop. Reactions anyone? Do you think the notion of general purpose networks one that's worth pursuing? Does anyone out there have other ideas on how to build such a beast? -- Jon Turner Washington University in St. Louis 314-889-6193 UUCP: jst@wucs.UUCP or ..!{ihnp4,seismo}!wucs!jst ARPANET: wucs!jst@seismo.ARPA CSNET: wucs!jst@seismo.ARPA%csnet-relay Brought to you by Super Global Mega Corp .com