Mark Wendt wrote: > On 09/29/2010 09:12 PM, Jon Elson wrote: > >> Igor Chudov wrote: >> >> >>> Things may have somewhat improved. >>> >>> I checked on my unsophisticated home network. Ping time (roundtrip), >>> involving three switches (one in my basement office, then the main >>> switch at the main interconnect in the utility room, then the switch >>> in the family room), and two linux boxes, is 0.21-0.34 milliseconds. >>> >>> >>> >> My understanding of ping is that it does NOT report the total round trip >> time through >> all nodes and switches, just the last hop. I think you need traceroute >> to see the delay >> at each hop. Still, 300 uS is not such a great time if you need 3 >> messages to propagate >> within one millisecond. >> >> Jon >> > > True, but I would hope in our environment we are only one-hopping > the signal between the computer and the machine/controller. > OK, but I consider a 1 KHz servo update rate to be the absolute minimum, and would like to keep open the possibility of raising that to 5 or 10 KHz. A network connection that makes even 1 KHz iffy seems like a real problem. What if you had two motion control cards that each had their own ethernet jack, then you'd need a hub, at least. And, I don't think 10-base-T hubs exist, they are all switches.
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