From Halopedia, the Halo wiki
Relay stations are communications relays part of a network capable of keeping a Halo installation functioning for many centuries. Relay stations are mostly automated, and can be abandoned and neglected for centuries without any impact to their operation.
All currently-observed relay stations share the same basic design and layout with only minor differences. Relay stations are built around rocky pillars, consisting of one large spinning center section which appears to be a some sort of dish receiver, a tall structure with many floors and an antenna-like structure on top, although the top can not be reached. Around the main structures, there are many other smaller structures and walkways that lead off from the middle, most of which lead back to the center. Relay stations are often built into rock pillars sticking out of the ocean, though the use of gravitic control systems allows them to be placed on floating platforms high above the surface of an installation. These elevated relays utilise slipspace translocation for safe and swift travel between the installation surface and the facility itself. At least one relay station was capable of, when activated, enabling a blue energy field around the central dish and emitting a beam towards the sky.
Relay stations were present on Installation 05 and likely the other Halo installations. When the High Prophet of Regret fled Earth, he was pursued by a number of UNSC vessels, including the corvette UNSC Coral Sea. To avoid discovery by the Covenant, the Coral Sea hid close to Delta Halo’s surface and devoted most of its time to scanning the ringworld. The crew discovered several communication relays across the installation’s surface and acquired information that is now used to reconstruct Delta Halo locations for research and War Games.
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