On 09/30/2010 11:39 AM, Jon Elson wrote: > Stephen Wille Padnos wrote: > >> Jon Elson wrote: >> >> >> That's true, but is also generally not needed. Since you don't care how >> long it takes to get from switch 1 to switch 2 (unless you're >> considering eliminating one or more of them), you don't need to see the >> intermediate times. The time ping reports is the cumulative time. >> There's a program called "mtr" which gives a very nice display of ping >> times, by the way. >> >> > Well, I get huge differences between ping and traceroute for remote > nodes. The ping > might be 68 ms, but when I do traceroute, I get several nodes showing > 100+ ms delay > EACH. Now, maybe it is traceroute that is giving the horribly inflated > numbers. > >>> Still, 300 uS is not such a great time if you need 3 >>> messages to propagate >>> within one millisecond. >>> >>> >>> >> Note that ping is one outbound and one reply packet. The pinging >> machine has to get a response back before it can know the delay time. I >> don't know how ping calculates the delay time though - start of send to >> end of receive, end of send to end of receive, compensation for the >> number of bytes, etc. >> >> > I would assume it times from when the packet is queued to when the > checked reply packet > is handed back to ping. But, this is very apropos to a real time > controller sending a > request to a device and waiting to get a response back. (Ask for > encoder position, > get the position back, then send velocity update.) > > Jon But again, it really doesn't matter. Controller card to controller card via a crossover cable is a single hop, with no switch, router, hub, or media convertor latency.
Mark ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
