A Low Earth Orbiting "Pacsat" has been described in the past as an orbiting bulletin board system. This is an over- simplification A PACSAT is a multi-channel, full duplex device, with short periodic access times dictated by orbital mechanics. These attributes mandate a different approach than the standard command-line interpreter style of BBS if the full potential of a PACSAT is to be realized The authors propose a new methodology for a PACSAT, and have developed several new protocols to implement more efficient ac cess. These protocols all use AX.25, either in connected mode or with UI frames. This paper provides a description of the access model, and an overview of the new protocols Background The authors have been struggling with the question "How can we make the best use of a bandwidth-limited low earth orbiting digital store-and forward system with a worldwide, unstructured, heterogeneous user base since an amateur Packet Radio satellite was first discussed in 1982. We began on air experimentation with the UoSAT-2 (UO-11) Digital Communications Experiment in December, 1984. In the following five and one half years, we've looked at where a resource like a PACSAT best fits in to the network as a whole. As a result of our study, we are proposing the use of a broadcast protocol as the basic downlink method, and a file server" rather than a BBS application as the basic service offered This document provides a brief overview of these conclusions, the companion specification documents provide the implementation details
