OSI Layer 1,2,3,4

Physical layer: transporting bits between two machines
Data link layer: MAC addresses and switching
Network layer:Packets, ip addresses and routing
Transport Layer: UDP segments and windowing

Repeaters

Repeaters are used to increase the signal's strength so it can be transmitted and received over a greater distance without a loss in quality. These devices are used with networks to help the lines running between network devices to reach greater distances. Repeaters operate at the first layer of the OSI model which is the physical layer.