Repeaters operate within the physical layer of the OSI reference model and regenerate the signal . Repeaters are used in LANs MAN and WANs. They may be used to provide more flexibility in design of a network or to extend the distance over which a signal may travel down a cable. One example of a repeater is an Ethernet Hub.
The 5-4-3 rule is important when considering using repeaters (or 10BT hubs) to build a larger LAN. This rule states that a single Ethernet LAN should not have more than:
5 No path between any two end systems (network interface cards or other equipment) may cross more than FIVE Ethernet segments.
4 No path between any two end systems may cross more than FOUR Ethernet hubs or repeaters.
3 No more than THREE of the five segments on the longest path may be active segments (i.e. segments with more than two nodes and/or repeater ports). The remaining two segments must be point-to-point links.
Network Equipment (including Hubs and Repeaters)