A subspace relay network is a communications system used by many cultures for long-range data transfer.
The Federation operated such a network, stemming from the initial deployment of subspace amplifiers by the Earth Starfleet starship Enterprise. (ENT: "Silent Enemy", TNG: "Aquiel")
The Hirogen controlled a large network of similar stations, which stretched across the Delta Quadrant, and reached into Alpha and Beta Quadrants as well. (VOY: "Message in a Bottle", "Hunters")