DS-TP: Deep-Space Transport Protocol

Abstract

We present deep-space transport protocol (DS- TP), a new reliable protocol for deep-space communication links. DS-TP's main advantage is its ability to complete file transfers faster than conventional TCP, SCPS-TP and Saratoga. Therefore, missions with small connectivity time are greatly favored. Deep space communication links are characterized by long propagation delays, high BERs, intermittent connectivity (i.e., blackouts) and bandwidth asymmetries. Common approaches to deal with the above unique characteristics are: rate-based, open-loop protocols to deal with huge propagation delays; regular retransmissions to deal with high BERs; transmission suspension to deal with blackouts; SNACKs to deal with bandwidth asymmetries. We adopt some of the above approaches, namely, the open-loop, rate-based transmission and the SNACKs and focus on the optimization of the rest, namely, the retransmission strategy of the transport protocol to deal either with high BERs or with blackouts. More precisely, DS-TP includes the Double Automatic Retransmission (DAR) technique. DAR sends each packet twice, importing some intentional delay (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) between the original transmission and the retransmission. Therefore, in the presence of communication gaps (i.e., errors or blackouts), corrupted packets will eventually be replaced by the same correct packets that arrive with delay R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> . R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> , however, is much smaller than the traditional TCP-RTO value. Our theoretical performance evaluation results reveal that DS-TP presents high potential for deploy ability. In particular, we show that for PER=50%, DS-TP completes a file transfer in half time of a conventional protocol.