Later Ethernet moved away from CSMA/CD 1 and hubs towards point to point full duplex links and switches. This allowed networks to be made bigger than the limits imposed by CSMA/CD and also allowed multiple speeds to coexist. Bridges (later known as switches) were introduced allowing networks to be split into multiple collision domains. There was an isolation barrier to protect against issues caused by ground potential differences in long runs (twisted pair ethernet uses transformers, I belive coax ethernet used optoisolators and DC to DC converters)ĬSMA/CD worked fine on small 10Mbps LANs but it started to show the strain as speeds increased and networks got bigger. The physical layer was designed with far more careful termination to ensure signal integrity was maintained even over long runs. To ensure the collision detection worked properly they put restrictions on both minium packet size and the total size of the network. It was designed as a local area network standard, no one station was a master and they went for a carrier sense multiple access system with collision detection. USB gradually evolved to add higher speeds and full duplex but longer distance was never a design goal.Įthernet (in it's early form) had a different set of design criteria. On the hardware side they went for a non-isolated differential signaling system which took some shortcuts on termination. So on the protocol side they went for a simple half duplex "speak when you are spoken to" protocol with small packet sizes. Support for long cable lengths was not a priority.
The priorities included low cost, low power consumption and passing high priority traffic with low latency.
USB was designed to replace various PC perhiperal interfaces including things like keyboards and mice.
0 kommentar(er)
