A repeater can connect Ethernet segments operating at the same transmission speed together to create a larger LAN. The repeater regenerates the signal as it passes from one segment to another. The 5-4-3 rule is important when considering using repeaters (or hubs) to build a larger Ethernet LAN:
5 - No path between any two end systems (NICs or other equipment) may traverse more than FIVE Ethernet segments.
4 - No path between any two NICs may traverse 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 passive point- to-point links.
The 5-4-3 rule applies to the furthest connection between NICs connected across the LAN. In practice, by choosing a suitable design, a large number of hubs and repeaters may be combined to produce a required network topology.
Connecting more segments or segments with different speed of operation requires the use of an Ethernet Bridge.
See also:
A page shows examples of various types of networking equipment, including Bridges and Switches for Ethernet.