TCP's protocol radius: the distance where timers prevent communication

Abstract

We examine how the design of the Transmission Control Protocol (TCP) implicitly presumes a limited range of path delays and distances between communicating endpoints. We show that TCP is less suited to larger delays due to the interaction of various timers present in TCP implementations that limit performance and, eventually, the ability to communicate at all as distances increase. The resulting performance and protocol radius metrics that we establish by simulation indicate how the TCP protocol performs with increasing distance radius between two communicating nodes, and show the boundaries where the protocol undergoes visible performance changes. This allows us to assess the suitability of TCP for long-delay communication, including for deep-space links.