1 Priority-based Adaptive Shortest Path Routing for IP over LEO Satellite Networks Ömer Korçak * and Fatih Alagöz. † korcakom@cmpe.boun.edu.tr, alagoz@boun.edu.tr Boğaziçi University, Computer Engineering Department, P.K. 2 TR-34342 Bebek, Istanbul, Turkey Designing an efficient routing algorithm for LEO satellite constellations is crucial for optimizing IP over Satellite (IPoS) network resources. Since there could be many shortest paths between two satellites, an efficient routing algorithm should provide better utilization of these paths. For this purpose, we propose a Priority-based Adaptive Routing (PAR) technique, which distributedly sets the shortest path through a destination. In this technique, a direction decision is made at each hop by a priority mechanism, depending on the past utilization and buffering information about the links. We further make some enhancements on PAR, and propose ePAR algorithm that also accounts for the contentions between packets with different source-destination pairs. We explore the performances of PAR and ePAR algorithms based on an extensive set of simulations, and compared their performances with static and adaptive routing techniques as a reference. Obtained results show that while the proposed PAR algorithm is promising for use in LEO satellite networks, ePAR algorithm may be more suitable for MEO satellite networks. Nomenclature µ = priority metric α = coefficient of “link utilization ratio” in priority metric β = coefficient of “queue length” in priority metric δ = coefficient of “average dropped data” in priority metric u r = link utilization ratio u r sd = link utilization ratio of s-d traffic l q = average queue length d d = average drop ratio t = Length of the aging period Z x,y ,Z xy = zone representation u xy = user density of zone Z x,y h xy = host density of zone Z x,y C i = continent representation A = Aggregate traffic (packets per day) T(xy,tk) = traffic requirement from zone Z x,y to zone Z t,k a h = activity percentage in hour h I. Introduction LONG WITH the new trends in global telecommunications where the Internet traffic may hold a dominant share in the total network traffic, satellites may become more popular for IP networks. Especially for interactive internet applications, Low Earth Orbit (LEO) satellites may be utilized due to shorter round-trip delays and lower transmission power requirements as compared other satellite solutions; namely, Geostationary (GEO) and Medium Earth Orbit (MEO) satellite ones. Most of the LEO satellite constellations include direct inter-satellite links (ISLs) in order to provide communication paths among satellites. Routing is an important issue for efficient use of satellites and ISLs, increased throughput and decreased delay. There are several routing algorithms proposed for LEO satellite constellations. Ref. 1 deals with adaptive routing with a limited set of alternative routes. However, there may be many shortest paths in a mesh-like network which can be fully * Phd candidate and research assistant, Computer Engineering Dept., Computer Networks Research Laboratory. † Assoc. Prof, Computer Engineering Dept., Computer Networks Research Laboratory. A