100Mb/s ethernet on usb 1.1

Aug 24, 2004 1 Replies
M

Greetings:



(sorry for the cross post if not appropriate: similar queries were cross posted to these two groups)



I would appreciate info on the behavior of USB ethernet adapters which support 100 Mb/s ethernet when used on USB 1.1 hosts; manufacturers descriptions are lacking in specifics.



Some essential questions:


  1. Will these adapters negotiate 100 Mb/s when used on USB 1.1?
  2. If yes to (1) will there be a discernable speed improvement over 10 Mb/s (depending on available onboard buffers, etc?)
  3. Some mfgrs advertise full duplex only on 100baseT; are there USB adapters that will do full duplex on 10baseT?

All replies much appreciated.



Michael Grigoni Cybertheque Museum


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R

Why not? The process negotiates Ethernet capabilities for the devices, irrespective of abilities behind those interfaces. Of course, the developer could chose to have the product behave otherwise, but there's no benefit to doing so.

USB1.1 runs at 1.5MBytes/sec (12Mbps), so it's possible to see better performance with 100Mbps Ethernet. In practice, half-duplex 10Mbps Ethernet caps out just above 5Mbps (aggregate for both directions).

Full-duplex and auto-sensing are not part of the 10Mbps Ethernet spec. Some Ethernet chipsets support a configurable full-duplex mode for 10Mb, but it's prone to create tech support issues and only a fraction of the market would use / appreciate it. Far simpler to implement 10/100 into the product and let it auto-negotiate.

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