On 2011-12-27, Danny Mayer <[email protected]> wrote: > On 12/27/2011 1:16 PM, unruh wrote: >> On 2011-12-27, Danny Mayer <[email protected]> wrote: >>> On 12/26/2011 11:17 PM, ben slimup wrote: >>>> Thanks Danny for your reply, >>>> >>>> but is it a big problem, if the client round-trip packet comes from a >>>> different servers each time? why? >>>> >>> >>> Because NTP uses multiple packets to gain data on the round-trip delay, >>> jitter, etc. of each server it gets responses from. The round-trip delay >> >> No it doesn't. It uses one outbound and one inbound packet to get the >> delay time. Ie, one packet arrives at the server, and one exits the >> server. Now if you are talking about statistics, that is different, and >> using many will increase the jitter. If the two machines are "good" then >> their times should agree within the jitter anyway. >> >>> is different if it comes from different systems. In addition each system >>> has its own idea of what the correct time is and at the point that it >>> receives and sends out the reply packet. The resulting data points will >> >> Not if they are all synchronised to UTC. >> > > What UTC is is not necessarily exactly identical. NIST has one idea of > it and NPL (UK) has a slightly different idea. However that is not what
The ns scale difference is irrelevant to the synchronization of computers. That is us, not sub ns. > I was referring to. Each server gets its information from different > sources whether it's a refclock, GPS, another server, etc.. As such > these sources differ somewhat from each other and while NTP tries to get > the best answer possible, each server will have a slight different > answer to the question. They may be only milliseconds apart but they > will be different. No. They will be perhaps usec apart if we are talking about computers. ns if we are talking about atomic clocks. And that will simply disappear into the jitter of the network connections. > > Danny _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
