Performance analysis of Space Station communications protocols

The Space Station Freedom communications architecture, the Consultative Committee for Space Data Systems (CCSDS) advanced orbiting system (AOS) protocols, and the design of the protocol simulator prototype are discussed. The results from an initial performance analysis of the CCSDS AOS protocols based on processing time and throughput measurements from the protocol simulator are presented. These results illustrate how CCSDS AOS protocol processing is affected by packet size, CCSDS grades of service, and data type. It is demonstrated that neither procedure processing times nor throughput are noticeably affected by CCSDS grade of service. However, the inclusion of processing times for Reed-Solomon and CRC error coding and retransmission effects will change this result. It was found that the multiplexer procedure is the primary bottleneck point of the CCSDS procedures studied. Improved multiplexer performance can be achieved using packet sizes in which segmentation does not occur. It was also found that larger packet sizes provide a higher rate of throughput. However, when the effect of retransmission is considered, larger packet sizes may not provide the highest throughput