Light and electricity travel about one foot in a nanosecond. Therefore, after the electric signal for the first bit has traveled about 100 feet down the wire, the station has begun to send the second bit. However, an Ethernet cable can run for hundreds of feet. While an Ethernet can be built using one common signal wire, such an arrangement is not flexible enough to wire most buildings. Unlike an ordinary telephone circuit, Ethernet wire cannot be just spliced together, connecting one copper wire to another.
Ethernet requires a repeater.
A repeater is a simple station that is connected to two wires. When collisions occur, it repeats the collision as well. In common practice, repeaters are used to convert the Ethernet signal from one type of wire to another. In particular, when the connection to the desktop uses ordinary telephone wire, the hub back in the telephone closet contains a repeater for every phone circuit. Any data coming down any phone line is copied onto the main Ethernet coax cable, and any data from the main cable is duplicated and transmitted down every phone line.