IS USB a type of bus?

[Jasper Chow]

USB topology is a star-like pyramid. In my veiw, it has nothing to do with bus. Is it misnamed? Or for some other reason?

 

[srizbf]

usb is a bus.
star is bus topology.

 

[betwixt]

I too think it is 'poorly' named as you can't connect more than one physical device to the same port. You can however have several 'end points' on one physical device so perhaps that is why they call it a bus.

Brian.

 

[FvM]

It becomes a bus when active star points (hubs) are connected.

 

[Jasper Chow]

Thanks. FvM, another question. Both the ethernet and usb transmit data at a very high speed. The speed of Usb 3.0 is claimed up to be 4.8Gpbs, which is even higher than that of ethernet. why does usb transmit data via baseband digital signal, while ethernet has to carry data on modulated analogous signal?

 

[FvM]

why does usb transmit data via baseband digital signal, while ethernet has to carry data on modulated analogous signal?

I assume you are referring to 1000BASE-T ethernet standard, which is mostly used for wired 1 GBPS links.

It doesn't use modulation, but the workload is split over 4 twisted pairs, which are also operated in duplex mode through hybrids. But it's still using a ternary (RZ) analog base band signal similar to 10 and 100 MBit ethernet.



By reducing the rate per twisted pair to 250 MBPS, 1000BASE-T can span relative large distances with twisted pair cables. USB 3.0 "Superspeed" links are restricted to 3 m by specification.