Routing in the Space Internet: A contact graph routing tutorial

A Space Internet is possible, as long the delay and disruption challenges imposed by space environment are properly tackled. Because these conditions not well addressed terrestrial Internet, more capable Delay-Tolerant Networking (DTN) protocols algorithms being developed. In particular, principles techniques for routing among ground elements spacecraft in near-Earth orbit deep-space enacted Contact Graph Routing (CGR) framework. CGR blends a set of non-trivial algorithm adaptations, operations concepts, time-dynamic scheduling, specific graph models. The complexity that framework suggests need focused discussion to facilitate its direct correct apprehension. To this end, we present an in-depth tutorial collects organizes first-hand experience on researching, developing, implementing, standardizing CGR. Content laid out structure considers planning, route search management, forwarding phases bridging domains. We rely intuitive graphical examples, supporting code material, references flight-grade implementations details where pertinent. hope will serve valuable resource engineers researchers can also apply insights presented here topics DTN research.