NASA's international network of ground tracking and communication stations for space probes. It is the largest scientific telecommunications system in the world. The network consists of three deep-space communications complexes (DSCCs) at roughly equidistant locations around the Earth for continuous tracking.

Each DSCC maintains the equipment of its deep-space station. DSN is managed and operated by the Telecommunications and Mission Operations Directorate (TMOD) of the Jet Propulsion Laboratory.

http://deepspace.jpl.nasa.gov/ Clearly explaining the workings of the deep-space network (DSN), this site has articles, fact sheets, video clips, and a pictorial history of the DSN.