From Halopedia, the Halo wiki
Communications relays are UNSC planetary communications facilities. A single colony may have at least three local carrier hubs that connect to a primary communications facility responsible for interstellar communications. These relays also apparently manage connections to a planet's reconnaissance satellites. On Reach, the Visegrád Relay was one of the planet's three northern carrier hubs.
Due to their importance, communications hubs can be optimal targets for Insurrectionist attacks. In early 2552, rebels on Harmony disabled a relay and stole two dry-docked freighters. Similarly, it was assumed that the communications disruption at the Visegrad relay station on July 23, 2552 was caused by insurgents, before it was revealed to be the work of a Covenant advance party instead.
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