Modeling the RTT of bundle protocol over asymmetric deep-space channels

Delay/disruption-tolerant networking communications rely heavily on BP(Bundle Protocol),which uses the well-known approach of store-and-forward with optional custody transfer to deal with stressed communication environments.The use of BP and its performance in deep-space communication has been the subject of debate.The accurate estimate of file delivery latency(i.e.,RTT(Round Trip Time))is essential for efficient transmission control,reliable delivery,and bandwidth usage optimization of a protocol.In this paper,we present a performance analysis of BP running over UDPCL/UDP over deep-space channels,focusing on the RTT estimate,in the presence of highly asymmetric channel rates.Analytical models are built for the RTT estimate of the BP/UDPCL transmissions considering the effect of delay caused by space channel-rate asymmetry,and,channel impairment.The models are validated by file transfer experiments using a PC-based testbed.It is found that a smaller bundle size(if smaller than a calculated threshold)results in a longer delay in custody acknowledgment transmission,and thus,a longer RTT.