A Simulation Study of QoS for TCP over LEO Satellite Networks with Differentiated Services

A number of satellite communication systems have been proposed using geosynchronous (GEO) satellites, medium earth orbit (MEO) and low earth orbit (LEO) constellations operating in the Ka-band and above. The next generation broadband satellite systems will use fast packet switching with onboard processing to provide full two-way services to and from earth stations. New services gaining momentum include mobile services and high data rate internet access carried over integrated satellite-fiber networks. Provisioning of quality of service (QoS) within the advanced satellite systems is the main requirement. Currently, Internet Protocol (IP) only has minimal traffic management capabilities and provides best effort services. In this paper, we present broadband LEO satellite network QoS model and simulated performance results. In particular, we discuss the TCP flow aggregates performance for their good behavior in the presence of competing UDP flow aggregates in the same assured forwarding. We identify several factors that affect the performance in the mixed environments and quantify their effects using a full factorial design of experiment methodology. INTRODUCTION The rapid globalization of the telecommunications industry and the exponential growth of the Internet is placing severe demands on global telecommunications. This demand is further increased by the convergence of computing and communications and by the increasing new applications such as Web surfing, desktop and video conferencing. Satisfying this requirement is one of the greatest challenges before telecommunications industry in the 21 century. Satellite communication networks can be an integral part of the newly emerging national and global information infrastructures (NII and GII). In the past three years, interest in Ka-band satellite systems has dramatically increased, with over 450 satellite applications filed with the ITU. In the U.S., there are currently 13 Geostationary Satellite Orbit (GSO) civilian Ka-band systems licensed by the Federal Communications Commission (FCC), comprising a total of 73 satellites. Two Non-Geostationary Orbit (NGSO) Ka-band systems, compromising another 351 satellites, have also been licensed. Eleven additional GSO, four NGSO, and one hybrid system Ka-band application for license and 16 Q/V-band applications have been filed with FCC [1]. However, satellite systems have several inherent constraints. The resources of the satellite communication network, especially the satellite and the Earth station, are expensive and typically have low redundancy; these must be robust and be used efficiently. The large delays in geostationary Earth orbit (GEO) systems and delay variations in low Earth orbit (LEO) systems affect both real-time and non-real-time applications. In an acknowledgementand timeout-based congestion control mechanism (like TCP), performance is inherently related to the delay-bandwidth product of the connection. Moreover, TCP round-trip time (RTT) measurements are sensitive to delay variations that may cause false timeouts and retransmissions. As a result, the congestion control issues for broadband satellite networks are somewhat different from those of lowlatency terrestrial networks. Both interoperability issues as well as performance issues need to be addressed before a transport-layer protocol like TCP can satisfactorily work over long-latency satellite IP ATM networks.