On Tue, Apr 1, 2008 at 11:17 PM, Matt Garman <matthew.garman@xxxxxxxxx> wrote: > On Tue, Apr 01, 2008 at 10:24:19PM +0200, H. Willstrand wrote: > > On Tue, Apr 1, 2008 at 6:05 PM, Matt Garman <matthew.garman@xxxxxxxxx> wrote: > > > We're using multicast basically for some inter-processs > > > communication. > > > > Which protocol(-s) are in use? (UDP, IGMP, ...) > > UDP. FWIW, we're using the ACE_SOCK_Dgram and ACE_SOCK_Dgram_Mcast > objects from the ACE libraries (which, as far as I can tell, at > least in this situation, are just wrappers around system calls). > > http://www.cs.wustl.edu/~schmidt/ACE.html > > > > > We timestamp (and log, in a separate thread) all of our sends > > > and receives, and do analysis on the logs. > > > > Are timestamps sent in the broadcast? If so, can the timestamps be > > out of sync generating the "delays"? > > No, the timestamps aren't sent in the broadcast. I just send a > sequence number. So in my logging thread, I basically log something > like this: "sequence number n sent/received at time t". > > I wrote a simple Perl script to compare the send and recv timestamps > logged for each sequence number. > > Note that when I perform this test across two different machines, > the machines are sync'ed via NTP; we actually monitor clock > synchronization, and I can say with confidence that the clocks are > never more than a couple milliseconds off. But also, I'm performing > these tests on the same machine (i.e. sender == receiver), so clock > sync issues don't apply. > > Thanks again! > Matt > > I see no reason why UDP packages can be delayed in a LAN with low or medium utilization for several seconds, they will simply be lost. Nor do I know if Java or other programming languages are in use, but if so, for an example, a Java garbage collector can easily generate this type of delays. Br H. Willstrand -- To unsubscribe from this list: send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
