On Wed, Sep 29, 2010 at 12:36 PM, Jon Elson <el...@pico-systems.com> wrote: > Igor Chudov wrote: >> I think that the trend in industrial machines, is to use Ethernet as >> much as possible inside industrial machines. On the surface, it >> appears to be a very attractive option, with all devices hooked up to >> the network switch and communicating seamlessly, without the mess of >> wires. What are the implications of this for EMC? >> > In must cases, Ethernet is not a low-latency communications scheme. If you > use a switch, as opposed to a hub, then there is an added delay as the > complete > packet needs to be read in by the switch before it can be sent out the > appropriate > port. > > If this is loose real-time, like for coordinating various systems in a > machining cell, > robot arms, parts handlers, pallet changers, etc. then a few > milliseconds delay here > and there are insignificant. If it is for the primary motion control, > then I think the > latencies are too high. I looked at a stripped-down ethernet for > communication with > my PPMC boards, and the general consensus among some people who worked with > RT ethernet was that the idea of > send request, get response, send > update < all in one > millisecond, was just not possible.
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. PING freedom.chudov.com (75.146.106.185) 56(84) bytes of data. 64 bytes from 75-146-106-185-Illinnois.hfc.comcastbusiness.net (75.146.106.185): icmp_seq=1 ttl=64 time=0.306 ms 64 bytes from 75-146-106-185-Illinnois.hfc.comcastbusiness.net (75.146.106.185): icmp_seq=2 ttl=64 time=0.341 ms 64 bytes from 75-146-106-185-Illinnois.hfc.comcastbusiness.net (75.146.106.185): icmp_seq=3 ttl=64 time=0.210 ms 64 bytes from 75-146-106-185-Illinnois.hfc.comcastbusiness.net (75.146.106.185): icmp_seq=4 ttl=64 time=0.303 ms ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
