Different types of network cabling have their own maximum distance that they can move a data signal. In cases where a LAN must be extended beyond it maximum run for its particular cabling type, repeaters are used. Repeaters take the signal that it receives from the computers and other devices on the LAN and regenerates the signal in order for the signal to maintain its integrity while traveling along a longer media run that is normally possible.
Repeaters do not have any capability of directing network traffic or deciding what particular route that certain data should take, they are simply devices that sit on the network and boost the data signal that they receive. The problem with repeaters is that they amplify the entire signal that they receive, including any line noise. In the worst case scenario, they pass on data traffic that is barely discernable from the background noise on the line.