Editing Network topology (section)

===Repeaters and hubs===
A [[repeater]] is an [[Electronics|electronic]] device that receives a network [[signal]], cleans it of unnecessary noise and regenerates it.  The signal may be reformed or [[retransmission (data networks)|retransmitted]] at a higher power level, to the other side of an obstruction possibly using a different transmission medium<!-- technically bridge-to-bridge -->, so that the signal can cover longer distances without degradation. Commercial repeaters have extended [[RS-232]] segments from 15 meters to over a kilometer.<ref>U.S. Converters, [http://www.usconverters.com/rs232-repeater-extender RS232 Repeater]</ref> In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart.

Repeaters work within the physical layer of the OSI model, that is, there is no end-to-end change in the physical protocol across the repeater, or repeater pair, even if a different physical layer may be used between the ends of the repeater, or repeater pair. Repeaters require a small amount of time to regenerate the signal. This can cause a [[propagation delay]] that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters that can be used in a row, e.g., the Ethernet [[5-4-3 rule]].

A repeater with multiple ports is known as hub, an [[Ethernet hub]] in Ethernet networks, a [[USB hub]] in USB networks.
* [[USB]] networks use hubs to form tiered-star topologies.
* Ethernet hubs and repeaters in LANs have been mostly obsoleted by modern [[network switch|switches]].