ColdSel: A selection algorithm to mitigate congestion situations over nanosatellite networks

Nanosatellites offer a solution to provide Internet access in areas where there is no ICT infrastructure, such as rural and remote areas, keeping low construction and maintenance costs. A nanosatellite constellation is composed of a certain number of nanosatellites distributed in one or more orbital planes. In most cases, this network cannot ensure an end-to-end connection between sources and destinations, because not all satellite links are up at the same time. The Delay and Disruption Tolerant Networking (DTN) paradigm is so necessary to deal with predictable disruptions and large delays, allowing nanosatellites, Internet gateways (also called hot spots), and rural gateways (also called cold spots) to keep data stored in their buffers also for tens of minutes waiting to be forwarded. We focused our attention on a possible selection strategy which indicates to all nanosatellites how many bundles (PDUs of the DTN protocol) they can upload from rural gateways during each contact. The decision is made by considering the maximum amount of data that nanosatellites and cold spots can exchange during each contact (quantity related to contact durations) and the possible presence of congestion situations in rural and remote areas or in nanosatellites. The proposed strategy is called ColdSel: it calculates the amount of bundles that each cold spot has to upload on the nanosatellite in contact with in order to mitigate congestion situations in rural areas and nanosatellites and to reduce the nanosatellite buffer occupancies so improving the performance in terms of data delivery time.