[ntp:questions] NTP setup in time sensitive environment

NVAP nvap23 at gmail.com
Wed Apr 22 22:24:41 UTC 2015


All,
I asked the following questions earlier this month but the provided
response did not help overcome the reported observations. So, kindly excuse
me for the repost.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
We are trying to setup NTP in our subsystem in a LAN environment for
time-sensitive systems.
But, we are facing some challenging issues in terms of minimizing the time
offset from the NTP time server.

*Setup:*
PC_V syncs to an external NTP time server PC_NTP which could be within the
same network or could be an external time server listed on NTP.org
PC_A and PC_B sync to PC_V which are in the same isolated subnet since PC_A
and PC_B are not exposed to external network.
PC_A, PC_B, PC_V could restart atleast once a day and might even be
restarted few times a day.
All PCs have Windows 7 x64 bit installed, have gigabit network with no
network congestion and we are using ntp 4.2.8p1.

*NTP Commands used:*
*Sync: *ntpd.exe -g -N -q -c "Sync Config file"
*Drift:* ntpd.exe -g -N -c "Drift Config file"

*NTP Configuration:*
*Sync Config file includes:*
server xxxx iburst burst
*Drift Config file includes:*
server xxxx burst minpoll 3 maxpoll 6 prefer true
tinker step 0
tinker panic 0
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

*Requirements: *Requirement is to setup NTP on these PCs in such a way that:
1) Time Sync between PCs as accurate as possible,  lets say within +/-5ms.
2) Time Offset between PCs shall remain as low as possible for as long as
possible, lets say within +/- 5ms offset for 24 hours.
3) PC_V might be able to talk to only one NTP time server within network,
lets say at stratum level 5.
But, it is important to keep the time offset as low as possible, lets say
within +/- 5ms offset.

*Actuals:*
1) Time offset between PCs after Time sync could be within +/- 100ms.
2) The clocks could have an offset of +/- 60ms within few mins after sync.
Even on overnight runs using loopstats and peerstats, we see that the
offset of system time from NTP time could be +/-50ms.
3) As per the following link, we should be using atleast 4 time servers for
maintaining accuracy:
http://support.ntp.org/bin/view/Support/StartingNTP4
But how do we assure that the time offset is minimal.

*Questions:*
1) How can we assure that the sync will consistently result in +/- 5ms
offset?
2) This seems to defeat the whole purpose of synching if the offset cannot
be maintained!
Is there a way to force the system offset to remain within +/-5ms?
3) Can we live with just 1 time server PC_NTP and PC_V, PC_A and PC_B will
closely following that time no matter?
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Thank you all.
NVAP


More information about the questions mailing list