DTN LEO Satellite Communications through Ground Stations and GEO Relays.

LEO satellites are characterized by intermittent connectivity with their ground stations. Contacts are short and separated by long intervals, which with urgent data can become a critical factor. To solve this problem, the use of GEO satellites as relay has recently been suggested. This solution is appealing, but has some limits, especially with polar orbits, as the link between the LEO satellite and the GEO relay is affected by long disruptions over polar regions. Moreover, the bandwidth available may be limited and difficult to fully exploit. In this paper, we show that GEO relays are complementary rather than alternative to ground stations, and that the enabling technology for their combined use is DTN (Delay-/Disruption- Tolerant Networking) architecture and related protocols, including CGR (Contact Graph Routing). To demonstrate this, a series of experiments carried out on a testbed running ION, the NASA implementation of the DTN protocols and CGR, is discussed in the paper.