The repeater is a station facility that makes its station a relay in the Infonet, the network that carries orders and messages to ships. It covers its own system and the systems one jump away, and passes packets on across them, but it is not a command post: no order enters the Infonet there.
It is cheaper than an uplink, built from antennas and frames. Only a relay can hold one. It needs no power, and relays while its station is not disabled.