Large Networks: 5-4-3 Rule

by Johannes Helmig [Published on 28 Oct. 1997 / Last Updated on 28 Oct. 1997]

A network is also limited in its maximum size, when Repeaters and/or hubs are used to extend a Thin Ethernet (10base2) or Twisted Pair Ethernet (10baseT/UTP) network, on large configurations, a Switch may become necessary to optimize network utilisation..

On Thin-Ethernet, the rules are:

- minimum 0.5 m between T-connectors
- maximum 185 m cable length
- maximum of 30 nodes (i.e. connections)

An cable can be extended by installing Repeaters, which amplify the signal:

A Repeater counts on each segment as a node and can be connected at ANY location in the Thin-Ethernet cable.
However, if a network needs more than 2 repeater:

the following limitations apply:
When an Ethernet signal travels from its source to destination station, it can travel through:
- maximum of 5 segments
- maximum of 4 Repeaters/hubs
- maximum of 3 populated segments
(Populated segments have more than 2 nodes connected, un-populated segments have only a node at each end, so a 10baseT-segments is a non-populated segment).

And for this discussion, a 10BaseT-Hub is like a repeater and a 10baseT cable can be treated as a cable 10base2-cable with just 2 systems on it.

There can be more repeaters/hubs in the complete network, and an Ethernet signal can pass-by more than 4 Repeaters/hubs, as long it does not have to go THROUGH more than 4 Repeaters/hubs.

If these rules are violated, the network becomes unreliable.

See Also

The Author — Johannes Helmig

Dr.Johannes Helmig is working as Director, Technical Knowledge Management in the Belgium office of Gerber Technology where he is involved in Customer Service and internal training, with special interest in Networking.


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