Protocol Testing of SCPS-TP over NASA´s ACTS Asymmetric Links

As the transport layer protocol of the Space Communication Protocol Standard (SCPS) suite, SCPS-Transport Protocol (SCPS-TP) is actually transmission control protocol (TCP), with a set of extensions aimed at improving TCP performance in space communications. Some work has been done on the performance evaluation of SCPS-TP in comparison with TCP. However, those works have been done by testing SCPS-TP via emulation test-beds. We present the file transfer experimental work of testing the SCPS protocol stack over NASA´s geostationary orbit (GEO) Advanced Communications Technology Satellite (ACTS). Considering that space communication channels in practice are frequently asymmetric in terms of channel bandwidth, our work is concentrated on the evaluation of the effectiveness of SCPS-TP in coping with channel rate asymmetry. We conclude that SCPS-TP is better suited than TCP over long-delayed, asymmetric, satellite channels with a throughput advantage of over 30 Kbyte/s for the transmission of a 10 Mbyte file. A hybrid of the channel rate control and acknowledgment frequency reduction mechanisms makes significant contributions to the performance enhancement of SCPS-TP over asymmetric space channels.