Transport protocols for Internet-compatible satellite networks

摘要

We address the question of how well end-to-end transportnconnections perform in a satellite environment composed of one or morensatellites in geostationary orbit (GEO) or low-altitude Earth orbitn(LEO), in which the connection may traverse a portion of the wirednInternet. We first summarize the various ways in which latency andnasymmetry can impair the performance of the Internet's transmissionncontrol protocol (TCP), and discuss extensions to standard TCP thatnalleviate some of these performance problems. Through analysis,nsimulation, and experiments, we quantify the performance ofnstate-of-the-art TCP implementations in a satellite environment. A keynpart of the experimental method is the use of traffic models empiricallynderived from Internet traffic traces. We identify those TCPnimplementations that can be expected to perform reasonably well, andnthose that can suffer serious performance degradation. An importantnresult is that, even with the best satellite-optimized TCPnimplementations, moderate levels of congestion in the wide-area Internetncan seriously degrade performance for satellite connections. Fornscenarios in which TCP performance is poor, we investigate the potentialnimprovement of using a satellite gateway, proxy, or Web cache ton“split” transport connections in a manner transparent to endnusers. Finally, we describe a new transport protocol for use internallynwithin a satellite network or as part of a split connection. Thisnprotocol, which we call the satellite transport protocol (STP), isnoptimized for challenging network impairments such as high latency,nasymmetry, and high error rates. Among its chief benefits are up to annorder of magnitude reduction in the bandwidth used in the reverse path,nas compared to standard TCP, when conducting large file transfers. Thisnis a particularly important attribute for the kind of asymmetricnconnectivity likely to dominate satellite-based Internet access