[ntp:questions] Comparison between ntpd and TSCclock

Unruh unruh-spam at physics.ubc.ca
Wed May 14 18:53:52 UTC 2008


eugenemil at sbcglobal.net writes:

>Developers at the University of Melbourne have produced a time-sync
>client called "TSCclock" which exchanges standard NTP packets with a
>NTP server.  They assert that TSCclock, which runs on FreeBSD and at
>least two flavors of Linux (Ubuntu and Fedora), provides substantially
>better synchronization than ntpd both on a LAN and over the Internet.

>The following info is some of what is available:

>1. The TSCclock page at the University of Melbourne:
>http://www.cubinlab.ee.unimelb.edu.au/tscclock/

>2. A paper titled "Ten Microseconds Over LAN, for Free", originally
>presented at the 2007 International IEEE Symposium on Precision Clock
>Synchronization for Measurement, Control and Communication.  This is
>available at
>http://www.cubinlab.ee.unimelb.edu.au/~darryl/Publications/ISPCS07_camera.pdf
>It includes a general description of their approach and results for
>both ntpd and TSCclock obtained in their testbed.

The paper suffers from talking nonesense. NTP is certainly better than 1ms
on a lan, and their data shows that the jitter is around .1-.2 ms.
Exagerating the difference does not do them any favours. 

Note that chrony ( a 10 year old system) already gives 10usec for free on
the lan. 

Futhermore their poll interval for their system is much higher than that of
ntp. I get about .05 msec jitter for ntp  on a lan, at least on my testbed. 
The ideas are interesting ( certainly their attempt to compensate for
network jitter, their chief difference from ntp, is far superior to the
clock filter approach of ntp, and I suspect superiour to the "weighting"
approach of chrony ( the data is weighted by the inverse of the delay)




>3. A one-hour Google Tech Talk: http://www.youtube.com/watch?v=o3nXgeh7v_U

>All of the info on TSCclock that I have run across has originated with
>the group at the University of Melbourne.  Does anyone know of an
>independent comparison between ntpd and TSCclock?

>Thanks,
>Gene




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