Broadcast file distribution protocols for satellite networks

Presents results of evaluations carried out at the University of Essex of broadcast file distribution protocols for packet satellite networks. Satellite networks are particularly suitable where a connection is required quickly or only occasionally, or where files are to be distributed over long distances or across difficult terrain. The inherent broadcast capability offered by a satellite transponder can be used to good effect in minimising the number of packets required to distribute a file to many recipients. However, there are special problems because of the propagation delay (about 250 ms for a satellite in geostationary orbit) suffered by data packets and acknowledgements travelling to the satellite and back, and this delay influences the acknowledgement strategies used. The authors first show how making use of the broadcast capability improves on the performance of repeated file transfer to each of the recipients in turn. Then they discuss a number of acknowledgement strategies. Finally, they show how the various strategies compare, and suggest improvements and discuss which are the most appropriate for a variety of scenarios