An Experimental Analysis of Checkpoint Timer of Licklider Transmission Protocol for Deep-Space Communications

As the main data transport protocol of delay-disruption-tolerant networking (DTN) targeting deep-space communications, Licklider transmission protocol (LTP) is developed to provide reliable and highly efficient data delivery over unreliable communication channels that are characterized by very long delay and/or frequent and random link interruptions. A checkpoint (CP) segment of LTP is sent, with a timer set (or simply, CP timer) to check the arrival status of the entire data block at the receiver, and it is retransmitted upon the expiration of the CP timer prior to reception of an acknowledgment. In the previous work, an analytical model is built for the CP timer setting in such a way that reliable file delivery in deep space is ensured with a minimum number of retransmission attempts taken for energy-efficient deep-space communications. However, the model was not validated. In this paper, a packet-level analysis based on realistic file transfer experiments using a PC-based testbed is presented to validate the built model for LTP in deep-space communications characterized by a long latency and highly asymmetric channel rate.