A Study On Licklider Transmission Protocol (LTP) For Space Communications

Delay/disruption tolerant networking (DTN) is considered a suitable technology to handle challenging communications in space environment. Channel-rate asymmetry is one of the main challenges in space communications. Little work has been done in investigating how to accommodate highly asymmetric channels for use of DTN in space. In this thesis, a study of DTN Licklider transmission protocol (LTP) in space communication environment characterized by asymmetric channel-rate is presented.A PC-based experimental Testbed was built in order to create a more realistic space communication environment for the proposed study. A DTN implementation named Interplanetary Overlay Network (ION), developed by the Jet Propulsion Laboratory (JPL) in US, was adopted to conduct the file transfer experiment for the proposed study. This work focuses on an investigation of aggregation of multiple bundle protocol (BP) bundles within a single LTP block for channel-asymmetric space communications. The intent is to find the number of bundles to be aggregated for the best goodput performance. A channel ratio threshold is derived considering the lengths of an aggregated data block and an ACK packet, and channel rates, and it must be maintained to avoid delay of ACK transmission of DTN LTP due to space channel asymmetry. In addition, a performance comparison between LTP and TCP is conducted to investigate which DTN CLA is more suitable for cislunar communications in presence of a long link delay, highly channel-rate asymmetry and high channel BER.