On 10/25/2016 12:16 PM, Nicklas Karlsson wrote: >> True dat. But why take the chance and not use a direct connection with >> a cross-over cable? Typical UDP traffic in a switched LAN is fairly >> fast but not necessarily totally reliable. And over the years I've seen >> plenty of collisions on a switched network for both TCP and UDP. The >> difference being TCP has error correction and will resend the packet. > The most usual in real time systems is packets are sent periodically and > receiver know it will receive packets. If bandwidth should be used to the > limit UDP is a better choice but with plenty of bandwidth left over TCP might > be a better choice. > > Then I do real time systems usually I tolerate some lost packets. Usually the > old value is not useful then new value is received but if there is enough > time request resend would be good. > > > I guess the answer is it depend on available bandwidth and delay. You also > need a mechanism to queue up old data no more needed. > > In real time systems a queue is usually not good because if there is not > enough time it will start grow. If newest available data is used perfomance > may degrade but software will continue to run. > > > Nicklas Karlsson Under UDP, the receiver will receive packets, however under the protocol it doesn't know if it receives "all" the packets. UDP is kind of a send and forget protocol. If you want to make sure that all packets are received, the only way to go is TCP. UDP uses less bandwidth than TCP, though in reality the difference is quite small.
A queue is not real time. Real time is *now* not when the queue decides to send. Losing packets in a critical environment is not a good thing. Let's suppose a limit is hit and the controller calls for a stop in one packet. Oops, that packet got dropped. And the machine bangs into the physical stops. Not a good thing. If you are going to use UDP for critical situations, you're best off using a direct connect, getting rid of the latency of the LAN and talking directly to the Mesa card. Mark ------------------------------------------------------------------------------ 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
