The Wideband (packet satellite) network is an experimental 3 Mbit/s communications system developed under sponsorship of the Defense Advanced Research Projects Agency and the Defense Communications Agency. This system is being used to evaluate the use of packet transmission for efficient voice communication, voice conferencing, and integration of voice and data over a satellite channel. Each station in the Wideband network consists of an earth terminal (dedicated 5 m antenna plus associated IF/RF equipment), a burst-modem and codec unit, and a station controller. Station controllers provide interfaces to host computers (including packet speech sources) and manage the allocation of the satellite channel on a TDMA demand-assigned basis. TDMA demand-assignment is implemented using a reservation-based packet-oriented protocol capableof handling traffic at multiple priority levels. The channel protocol provides a reservation-per-message mode of service (datagrams) to support transmission from bursty traffic sources and a reservation-per-call mode of service (streams) to support traffic with more regular arrival statisticS (e.g., vioce). A distributed scheduler running in every station controller eliminates the need for a central control station and minimizes network transit delay for datagram transmission as well as stream creation, modification, and deletion. In this paper we describe the protocols and mechanisms upon which the Wideband packet satellite network is based.

We present a framework for considering the impact of satellite communications on high level computer communication protocols. Within that framework, we present a model for analyzing these effects, and using that model, we derive some bounds on the amount of data that may be transferred over a communication channel which contains a satellite link. As our example, we use the flow control mechanism of an early version of a planned NBS transport protocol.

This paper presents a comprehensive review of the ARPANET routing algorithm, from its original implementation to our plans for future modifications. We hope that by collecting this information, and by providing considerable details, we can provide others with a useful reference document concerning some of the practical problems of network algorithm design. Much of the discussion below assumes a basic familiarity with the principles of packet switching, the ARPANET implementation, and some of the relevant terminology, information which can be found, for example, in [4]. Sections 1 and 2 give a brief summary of basic routing concepts and of the original routing algorithm, respectively. The following two sections describe in detail subsequent modifications and the actual implementation currently in use. Section 5 then discusses some problems that have developed over the past few years, as network usage has grown considerably. The final sections outline some explanations for these problems and some mechanisms for improving performance. We are in the process of implementing these and other changes to the routing algorithm.