[ntp:questions] Re: This is tougher than I thought?

Richard B. Gilbert rgilbert88 at comcast.net
Tue Jan 24 15:39:05 UTC 2006

Axonn wrote:

>Thanks for answering, David, Danny, Maarten...
>David: I think you just saved my life since that code is really helpful
>and is pretty much exactly what I need. I can port it to VC++ or use it
>directly from VB. Thank you a lot!!!
>Danny: wasn't thinking at re-inventing the wheel anyway. But I didn't
>find any ready-to-use tools until David showed me that. I wouldn't have
>imagined NTP is such a big thing but I like it. I would study it more
>but I got a software to finish and priorities to set. I just wanted a
>piece of mind from you experts in this matters. And you really saved me
>of a lot of hours of dirt digging probably.
>Some more questions:
>1. I know this is a stupid question probably, but I'm still gonna ask
>it: synchronizing via SNTP should discard network latencies right? So
>if I got a lag of 5 seconds to a server, I should still get the time
>within a pretty accurate margin.
If you get a "lag" of five seconds, you are using the wrong server or an 
extremely poor network connection!  The potential error in transmitting 
time from server to client is equal to one half of the round trip 
delay!  Typical round trip delays, using a broadband internet connection 
(cable or ADSL), are in the range of ten to fifty milliseconds!

>2. Why do some servers have "stratum" = 1 and other = 2?
Stratum one servers get their time directly from an "atomic clock".   
Stratum two servers get their time from one or more stratum one 
servers.  Stratum two servers frequently provide better time than 
stratum one servers because the stratum two servers and their network 
connections are not a heavily loaded as the stratum one servers.  IOW, 
stratum is a measure of "distance" from the atomic clock, rather than a 
measure of the accuracy of the time you might obtain from a particular 

There are stratum three servers but these are seldom available to the 
public; usually they are operated by small businesses for their own 
internal use.
Any server with a stratum of four or greater is probably serving its own 
unsynchronized local clock although ten is the conventional stratum in 
this case.

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