[ntp:questions] Re: tinker step 0 (always slew) and kernel time discipline

Joseph Gwinn JoeGwinn at comcast.net
Sun Sep 24 17:04:54 UTC 2006

In article <IJSdnV6hOrl5cYjYnZ2dnUVZ_uWdnZ2d at megapath.net>,
 hmurray at suespammers.org (Hal Murray) wrote:

> >> The telephone companies tend to be very aware of time and timing.  The 
> >> time division multiplexing of T1 and T3 lines requires splitting the 
> >> second very precisely.  Cellular phones also require very precise 
> >
> >That can be true of the public network, although even then it may
> >be more so for the more engineering oriented layers, like bearer
> >synchronisation, than the more commercial oriented layers, like
> >call detail recording.
> >
> >However, it is very definitely not true of most PABX systems, which
> >typically have wristwatch and eyeball set times and run in local
> >time, with no automatic daylight saving switch, and have no high quality
> >frequency standard.
> There are two separate issues: time and frequency.
> Anybody know if I can get a good frequency off a DSL line?
> Assume I'm willing to hack a wire into my modem/router.
> If so, it might be a nice/cheap way to get a stable clock
> to use with a NTP box.  (Handwave, PLLs and such.  Not a hard
> problem.)

I assume that DSL follows a public standard, and that this standard will 
specify how good the clocks must be.

For comparison, broadband cable modems follow DOCSIS 2.0, available from 

My understanding is that both are timed protocols of some kind, but I 
don't know the details.

Joe Gwinn

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