Hubs and topology

Ethernet hubs (multiport repeaters) change the topology, but not the fundamental constraints. Hubs enabled the model in which each station now had its own link to the wiring closet. Loops are still forbidden. The maximum diameter of an Ethernet consisting of multiple segments joined by hubs is still constrained by the round-trip-time, and the need to detect collisions before the sender has completed sending, as before. However, the network “diameter”, or maximum distance between two hosts, is no longer synonymous with “total length”. Because twisted-pair links are much shorter, about 100 meters, the diameter constraint is often immaterial.