Design and specification of the Xpress transfer high-speed protocol

Abstract

The use of fiber optics in high-speed data networks has significantly increased throughput and reliability at the physical layer. Consequently, the transport layer has become a bottleneck to the data transfer potential of highspeed networks. This bottleneck has forced an investigation of transport protocols and standards to be used in future networks. The Xpress Transfer Protocol (XTP) is a transport layer protocol designed to perform efficiently in networks where high data rates, densely packed bit pipes and low bit error rates are normal operating conditions. However, XTP is a relatively new protocol which has not yet undergone extensive testing and analysis to verify its ability to resolve the transport layer bottleneck. In this thesis the specification and analysis of the XTP protocol, using the System of Communicating Machines (SCM) model is presented. A comparison is then made with an alternative high-speed protocol called SNR, originated at AT&T Bell Labs. Based on this study, it is concluded that the XTP protocol provides several mechanisms, such as rate control and extended sequence numbering, that should be included in developing high-speed transport protocols. Furthermore, it is concluded that XTPs flexible characteristics allow for multiple paradigm implementations at the cost of some complexity, making a more complete analysis of this protocol difficult. As work on high-speed transport protocols continues many of the XTP mechanisms should be considered for inclusion into evolving standards. It is also concluded that there are some critical features for high-speed protocols that are not in XTP.