Command operation procedures (COPs) are protocols operating in the transfer layer of the telecommand and telemetry architectures designed by the International Consultative Committee for Space Data Systems. The authors present an evaluation of virtual frame transmission times, throughput efficiency, buffer occupancy, and waiting times for the COP-2. COP-2 represents an ARQ-type (automatic repeat request) protocol with checkpointing that is comparable to the checkpoint mode protocol. A discrete two-class priority service model with random server interruptions is considered. The analysis is based on the concepts of level crossing analysis as defined in J.W. Cohen (1977) and J.G. Shanthikumar (1981). The results of this work will be used by the European Space Agency as design guidelines for the European Data Network.>

The definition of a backchannel architecture for open systems interconnection over satellite links has been the subject of the SENS-project1 The new proposal is based on existent international standards and uses the options of the ISO-class 4 transport layer protocol in order to enclose in level 4 data link control functions for unidirectional satellite links following the rules of the IBM-checkpoint protocol. This paper provides performance values of the SENS architecture in comparison with those of common satellite communication systems. With means of elementary probability theoretical methods an approximate analysis of the IBM-checkpoint protocol is accomplished. The results show that for large amounts of data the new architecture proves to be best suited for cost efficient use of public satellite data links.