All switches do at least store and forward today. Even the $20 cheap ones. We use ethernet for real time control in some of our products. Faster loop time than LinuxCNC. We use raw ethernet frames so that we don't even need the ethernet stack (no DNS/etc needed either.) We also run web services on the same products (ARM based) that run the IP stack and coexist peacefully.
Don't run ALL the computers in your office and the real-time network on the same switch. real time stuff on one switch, rest of office on another, and one cable between the switches. The real-time one will never see much traffic (except broadcasts.) We do it. It works. We actualy have the opposite problem. If we do even 1khz broadcast packets w/ real-time it drives office wifi *NUTS* and crashes. FWIW, There is no way to do an encrypted wifi broadcast. Everyone has different keys and this the access port has a ton of encryption to do (plus it never lets your phones go to sleep so the batteries die FAST.) VLAN tagging solves the broadcast/wifi issue but thats no longer a $20 switch. Watchdog timeouts solve too many missing packet problems. IEEE1588v2 solves most jitter problems if timing is critical. Embedded parts seem to all support it now. We implemented it but have not needed to use the actual correction factors yet as our control style is fairly robust against jitter (but its there if we ever need it.) Stephen On Tue, Oct 25, 2016 at 11:26 AM, Przemek Klosowski < przemek.klosow...@gmail.com> wrote: > On Mon, Oct 24, 2016 at 10:42 PM, Stephen Dubovsky <smdubov...@gmail.com> > wrote: > > Why would UDP need resends on a shared ethernet port? There are no > > collisions on a full-duplex port & switch (which is pretty much ALL of > them > > now-a-days.) Passive hubs went the way of the dodo. > > Of course, but you are assuming an ideal active switch, and that may > or may not be the case. All the switched ports are sitting on an > internal bus, whose bandwidth has to be better than N/2*individual > port bandwidth, because in principle, all port pairs could be active > at the same time; on a cheap switch that 'bisection' bandwidth may not > quite be there. Also, in general, two originators could be trying to > talk to the same receiving port and collide on it---switches of course > must implement some form of 'store and forward' to be able to decide > where to switch the packet to, but cheap switches do not have a deep > store queue---maybe they can handle one or two packets but not more > than that. So, in practice, the collisions and dropped packets are > possible. > > ------------------------------------------------------------ > ------------------ > The Command Line: Reinvented for Modern Developers > Did the resurgence of CLI tooling catch you by surprise? > Reconnect with the command line and become more productive. > Learn the new .NET and ASP.NET CLI. Get your free copy! > http://sdm.link/telerik > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ The Command Line: Reinvented for Modern Developers Did the resurgence of CLI tooling catch you by surprise? Reconnect with the command line and become more productive. Learn the new .NET and ASP.NET CLI. Get your free copy! http://sdm.link/telerik _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
