Ethernet and IEEE 802.3 implement a rule, known as the 5-4-
3 rule is also known as the IEEE way, for the number of 
repeaters and segments on shared access Ethernet backbones 
in a tree topology. The 5-4-3 rule divides the network into 
two types of physical segments: populated (user) segments, 
and unpopulated (link) segments. The 5-4-3 rule is also 
known as the IEEE way and is sometimes compared to the 
Ethernet way which is having 2 repeaters on the single 
network without having any hosts connected to a repeater.

5 Segments
4 Repeaters
3 Populated Segments
2 Unpopulated Segments
1 Collision Domain