Modeling Memory-Variation Dynamics for the Licklider Transmission Protocol in Deep-Space Communications

Delay/disruption-tolerant networking was developed to enable automated network communications despite the long link delay and frequent link disruptions that generally characterize deep-space communications. It uses the well-known approach of store-and-forward with optional custody transfer, in which a node agrees to hold a file in memory (or storage) until its successful reception is acknowledged by the next node. The performance and memory consumption of delay/disruption-tolerant networking's Licklider transmission protocol (LTP) and bundle protocol in deep space will bear on decisions to adopt this technology. There is currently an urgent need to evaluate the performance and memory dynamics for file transmission by LTP and bundle protocol. In this paper, we present a study of memory dynamics for LTP-based transmission in a typical relay-based deep-space communication system characterized by an extremely long signal-propagation delay, lossy data links, and asymmetric data rates. Analytical models are built to quantify the dynamics of memory occupancy/release and memory release latency imposed by the use of LTP for reliable and complete file delivery in deep-space missions. File-transfer experiments are conducted using a test bed to validate the models.