Relay station
From Halopedia, the Halo wiki
Relay Stations are facilities built by the Forerunners on their Halo fortress worlds. These relay stations are part of a network that has kept Installation 05 functioning for untold centuries. The only one encountered so far consists of some sort of communication tower and what appears to be large Forerunner dish receiver. The multiplayer map Ascension is just one of many stations on the Halo.
Relay stations appear to be part of the highly complicated matrix of the systems on a Halo, being part of a network of stations that keep them running smoothly. They consist of one large spinning center section that may be the only part that does anything, but what it does is unknown, a tall structure with many floors, although the top can not be reached and there are many other smaller sections that lead off from the middle, usually taking you back to the position where you started.
