[chrony-dev] Issue with version 1.25 and GPRS/GSM connections

[Harald Krammer <Harald.Krammer@xxxxxx>]

Hello,
I am using Chrony 1.25 and got a strange problem in the field. 
So it can happen that the time synchronisations stops after few 
hours. A restart of Chrony helps to get the synchronisations working 
again, but the reason for that behaviour isn't clear to me. I can not 
reproduce it, but I'm assuming this issue exists only on  
GPRS/GSM connections (->high jitter).

Wireshark-Capture in case of the problem:
http://hkr.at/ntp.pcap

- packet number 1-21: Chrony session seems "OK" to me
  I saw a high network jitter (from GPRS connection)
- packet number 21: Chrony starts asking of NTP request. 
- Packet number 29: Chrony gets to state synchronised 
- Packet number 35: Chrony send out Ref-ID from NTP Server
  Root delay is 1,47 s and Root dispersion 2,95 s
  slightly high
- Packet number 35: Chrony send out Ref-ID from NTP Server
  Root delay is 1,47 s and Root dispersion 6,07 s
  high
- Packet number 45: Chrony send out Ref-ID from NTP Server
  Root delay is 1,47 s and Root dispersion 82 s
- Packet number 45: Chrony send out Ref-ID from NTP Server
  Root delay is 1,47 s and Root dispersion 216 s
- Packet number 51: Chrony send out Ref-ID from NTP Server
  Root delay is 0 s and Root dispersion 0 s
  -> Local clock: 127.127.1.1 
  -> status remains in this state

Configuration:
server 10.62.22.106 iburst minpoll 6 maxpoll 8 prefered
driftfile /var/run/ntpd.drift
maxupdateskew 100
driftfile /var/lib/chrony/chrony.drift
keyfile /etc/chrony/chrony.keys
commandkey 1
pidfile /var/run/chronyd.pid
initstepslew 0.001 10.62.22.106  
local stratum 10
logchange 0.5
cmdallow 127.0.0.1

Tracking in case of the problem:
Reference ID    : 127.127.1.1 ()
Stratum         : 10
Ref time (UTC)  : Mon Aug  1 13:11:07 2011
System time     : 0.000000378 seconds fast of NTP time
Frequency       : 0.000 ppm fast
Residual freq   : 0.000 ppm
Skew            : 0.000 ppm
Root delay      : 0.000000 seconds
Root dispersion : 0.000003 seconds

Sources in case if the problem:
210 Number of sources = 1
MS Name/IP address           Stratum Poll LastRx Last sample
============================================================================
^? 10.62.22.106                  3    8   378m   -357ms[ -468ms] +/- 
765ms

Why is the time source marked as  unreachable? Request are still running. 


I played around with maxdelay, maxdelayratio and maxdelayratio but I got
also
an unsynchronised state and it remained. (e.g. maxdelay 5,...)
Any suggestion are welcome.

Nice greetings,
Harald



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