On 09/30/2010 08:48 AM, Kent A. Reed wrote: > 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. >
Looking at the man page for ping, the "old" behavior of ping was to report "user-to-user" time. The newer versions now report round-trip time. 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
