[ntp:questions] Win7: ntpd adjusting time backwards

Rick Jones rick.jones2 at hp.com
Tue Dec 11 21:23:11 UTC 2012


David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> On 11/12/2012 19:35, Rick Jones wrote:
> > Handwaving a bit... The query and the response seem to be
> > something like 90 bytes (including an Ethernet header). That then
> > is 720 bits.  At 3 Mbits/s that would be 0.24 milliseconds of
> > transmit time.  It would then be 0.024 milliseconds on the
> > downlink.  I suspect that asymmetry is dwarfed by either queueing
> > delays (bufferbloat) when either/both are active and/or the rest
> > of the delays from your system to the server(s).

> Yes, I see what you mean, but I was thinking of the whole network,
> and not simply the up and down speeds.  That we have a 10:1 ratio
> may suggest how the rest of that ISP's network is configured.  The
> delays in the cable modem, Samknows box, router and 1 Gb/s switch
> are likely to be far in excess of the 0.024 ms and even the 0.24 ms!

Well, I have zero direct knowledge of the internals of an ISP these
days, but my understanding of the/a rational behind the asymmetry to
the home has to do with allocating limited
bandwidth/frequency/spectrum on the physical plant from the ISP's end
to the home.

If the ISP's internal network (beyond the "head end" or what ever it
would be called) is built on more standard ethernet-ish things, I
would expect there to be equivalent bandwidth in each direction since
to my knowledge those things have symmetric bandwidth.  Of course that
doesn't guarantee symmetric routing...

rick jones
-- 
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
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