SCPS-TP, TCP and Rate-Based Protocol Evaluation For High Delay, Error Prone Links

Abstract

This paper describes testing performed to validate operation of Space Communications Protocol Suite Transport Protocol (SCPS-TP) relative to the specification and perform a comprehensive comparison of SCPS-TP protocol options to IP based protocols. Tests were performed at Glenn Research Center to validate the operation of SCPS-TP relative to the Consultative Committee on Space Data Systems (CCSDS) specification, to perform a comprehensive comparison of SCPS-TP protocol options to IP based protocols, and to determine the implementation maturity level of these protocols – particularly for higher speeds. The testing was performed over reasonably high data rates of up to 100 Mbps with delays that are indicative of near planetary environments. The tests were run for a fixed packet size, but for various errored environments. The results indicated that SCPS-TP congestion-friendly options perform slightly better than TCP SACK protocols at moderate and high error-rates. The results also show that existing standard transport protocols and capabilities (drawn from a variety of communities) appear to satisfy all known mission needs. INTRODUCTION In the late 1980’s and throughout the 1990’s, the Internet has rapidly developed allowing vast improvements in communication and networking. These technologies utilize packet-based communications rather than circuit-based communications. The Consultative Committee on Space Data Systems (CCSDS) foresaw the need to take advantage of this new Internet technology and developed the Space Communications Protocol Suite (SCPS) to address some specific issue related to space systems. Thus, the TCP/IP protocol suite was investigated and modifications to the networking, security and transport protocols were specified. These specifications as know as the SCPS security protocol , network protocol, transport protocol and file transfer protocol (SCPS-SP, SCPS-NP, SCPS-TP and SCPS-FP) PURPOSE There have been numerous debates regarding the actual improvements that SCPS may provide over the ever-evolving TCP/IP protocol suite. In addition, much of the SCPS initially testing and demonstrations often did not provide what many consider to be a valid comparison relative to TCP as known improvements to TCP for long bandwidth-delay networks were often not implemented (i.e. large windows, selective acknowledgements) [1]. Other testing often was performed over simulated links where SCPS would provide little advantage due to the very low bandwidths []. Some well documented and thorough testing has been performed at lower rates. These results correlate well with our test results [ 3,4 ]. In order to get a better understanding of the actual improvements, if any, that SCPS could provide relative to TCP and to determine the maturity of the various protocols for higher-rate links, the NASA Space and Data Communications Systems (SCDS) Office requested Glenn Research Center to perform a comprehensive set of tests. This paper is a summary of the comprehensive set of tests that are currently being documented in a NASA Technical Report [5]. This testing