In The Bus Topology, Two Nodes can not be permitted to transmit simultaneously due to interface. how Ethernet solve this problem?

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Last Post by rubberman

The internals of ethernet is a CSMA/CD (Carrier Sense Multiple Access w/ Collision Detection) protocol. Basically that is like where you have a door wide enough for 1 person, but more than one person wants to go through at a time - collision! So, everybody backs off for some random period of time and then they go though again. If another collision occurs, then they try again... When ethernet switches came into vogue, they could not change this protocol, but they could buffer and gate data between nodes over the switch so that collisions rarely, if ever, occur. In any case, ethernet itself does not change the underlying csma/cd protocol, but modern switches and NICs are smart enough to deal with it more efficiently. FWIW, this is why bus-based ethernet was never suitable for real-time factory controls, and most factory networks were either ARCnet or Token-Ring, which used collision avoidance and token passing, so deterministic behavior required for hard real-time networked systems was feasible. In fact, modern switches are so efficient that deterministic timing is now reasonable, allowing ethernet to pretty much take over the factory.

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