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 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. Danny _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
