Channel Delay Impact on CCSDS File Delivery Protocol (CFDP) over Space Communications Links

A substantially long round trip time (RTT) in space channel hurts TCP interactions between the sending and receiving ends. The consultative committee for space data systems (CCSDS) file delivery protocol (CFDP) is a new international standard developed to meet a comprehensive set of deep space file transfer requirements. There is a need in NASA to have controlled, experimental evaluation of CFDP performance in space, especially on its effectiveness in coping with long channel delay. This paper presents an experimental evaluation of channel delay impact on throughput performance of CFDP over LEO-satellite link, GEO-satellite link, and cislunar communication link in comparison with the widely deployed TCP and a space transport protocol, SCPS-TP. The experimental results show that CFDP/TCP in the deferred NAK mode is much more effective than other two stacks in the simulated point-to- point space communication links, especially when operated with a long link delay, a high BER and channel-rate asymmetry. We have found that CFDP/TCP is less sensitive, and FTP/TCP and SCPS-FP/SCPS-TP are highly sensitive, to the increase of link delay.