On distributed, geographic-based packet routing for LEO satellite networks

Thomas R. Henderson Randy H. Katz Geo ast Network Systems, In . Ele tri al Engineering and Computer S ien e Dept. 190 Independen e Drive University of California, Berkeley Menlo Park, CA 94025 Berkeley, CA 94720 Abstra t|Advan es in satellite te hnology are enabling the deployment of large onstellations of Low-EarthOrbiting (LEO) satellites. Next-generation systems will be tailored for broadband, pa ket-swit hed servi es, and therefore require either distributed or entralized pa ket routing me hanisms. Some resear hers have hypothesized that the semi-regular mesh topology of a polar-orbiting onstellation admits a simple distributed routing proto ol based on using geographi information embedded in the node address. In this paper, we take a loser look at this hypothesis in the ontext of ommer ially-proposed onstellation designs. Using simulation, we study a distributed routing proto ol that sele ts the next hop based on a minimization of the remaining distan e to the destination. Our numeri al results indi ate that this routing strategy usually yields good routes, with an average laten y degradation of less than 10 ms when ompared with the optimal route. However, there are lo ations in the topology, most notably around the ounter-rotating seams, the polar regions, and lose to the destination of a pa ket, where the assumption of a regular mesh topology breaks down and it is diÆ ult to guarantee robustness without adding signi ant additional omplexity to the proto ol. I. Introdu tion Low-Earth-Orbiting (LEO) satellite onstellations have begun to be deployed for voi e and narrowband data servi es. Although more ompli ated to design and maintain than satellites positioned at geostationary (GEO) orbit, LEO satellite networks o er the potential for smaller earth terminals (requiring less transmit power and antenna gain), lower ommuni ations laten y, and frequen y reuse. Future LEO networks will likely migrate to o ering broadband data servi es based on pa ket-swit hing and offer global onne tivity based on a network of intersatellite ommuni ations links (ISLs). The LEO network an be viewed as a spe ial type of mobile network, one in whi h the nodes move with respe t to the xed users. Despite its time-varying nature, the semi-regular mesh topology of polar onstellation ongurations has led resear hers to investigate the potential for exploiting the topology to simplify pa ket routing. Namely, by using geographi -based addresses, the hypothesis put forward is that a simple distributed routing protool that dire ts satellites to route pa kets in the dire tion that most redu es the remaining distan e to the destination an yield routes that are lose to optimal in terms of end-to-end laten y. In this paper, we report on a simulation study that has attempted to on rm the above hypothesis. We found that, in general, su h a routing strategy does admit good performing routes, with average laten y degradations of less than 10 ms (although with some instan es no more than 60 ms worse) for ommer ially-proposed onstellations. However, we found onstru tion of a robust protool based on this strategy diÆ ult, be ause of the breakThis work was supported by DARPA ontra t DAAB07-95-CD154, by the State of California MICRO program, and by Hughes Air raft, Metri om, Fuji Xerox, Daimler-Benz, and IBM. Overlap of coverage at the poles Cross-plane intersatellite links (ISLs) are turned off causes rapid ISL handoff Counter-rotating seam