The 5-4-3 Rule of ETHERNET

When Ethernet was developed it was recognized that the use of repeaters to connect segments to form a larger network would result in pulse regeneration delays that could adversely affect the probability of collisions. Thus, a limit was required on the number of repeaters that could be used to connect segments together. This limit in turn limited the number of segments that could be interconnected. A further limitation involved the number of populated segments that could be joined together, because stations on populated segments generate traffic that can cause collisions, whe   reas non-populated segments are more suitable for extending the length of a network of interconnected segments. A result of the preceding was the ‘‘5-4-3 rule.’’ That rule specifies that a maximum of five Ethernet segments can be joined through the use of a maximum of four repeaters. In actuality, this part of the Ethernet rule really means that no two communicating Ethernet nodes can be more than two repeaters away from one another. Finally, the ‘‘three’’ in the rule denotes the maximum number of Ethernet segments that can be populated. Figure illustrates an example of the 5-4-3 rule for the original bus-based Ethernet.