On 9/29/2010 Jon Elson wrote: > ontent-Type: text/plain; charset=ISO-8859-1; format=flowed > > 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 > Jon:
Are you sure about that? I thought ping worked by sending an ICMP packet containing a time stamp and comparing that time stamp with its time of receipt of the returned packet. When I look at a test case I just did in my local network with ping and traceroute I see the same r/t times. Maybe my network just isn't complicated enough? In any case, ping and traceroute use ICMP packets and I don't believe they exercise the full protocol stack. Last year when I was so confidently saying I meant to try out RTnet with RTAI, I intended to be sure I tested the full time through the stacks, application to application. I started to sketch out minimal programs, one for the sender that, like ping, creates and sends a time-stamped packet and analyzes the packet returned, and a second for the client, that receives a packet and sends it back. A background program, like the EMC latency test, would track the reported times statistically. Unfortunately, I didn't have any boards with the requisite ethernet chips back then, and my attention wandered as my grandkids got older:-) Regards, Kent PS - thanks for setting me straight on the Windows/NT issue in the EMC project. I'd forgotten. I can salvage some of my dignity by noting the result adds to my argument that we have to demand functionality. ------------------------------------------------------------------------------ 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
