[ntp:questions] Win7: ntpd adjusting time backwards

Jan Ceuleers jan.ceuleers at computer.org
Sat Dec 22 14:36:21 UTC 2012


On 12/11/2012 12:49 PM, David Taylor wrote:

Sorry: catching up.

> What happens if the link to the Internet is rather asymmetrical?  For
> example, here I am stuck with 30 Mb/s down, but only 3 Mb/s up.

The actual bitrate is not so important. True: it determines the time a
packet spends on the wire. But more important is (or can be) the amount
of time a packet spends in various queues before actually being sent.
This time varies with instantaneous network load, and with the size of
the queue. Google for "bufferbloat", and apologies if everyone here
already knows all of this.

Having said that: there can indeed be asymmetrical transmission delays
that are linked to the technology being used. My VDSL2 modem tells me
that the downstream delay is 14.1ms and the upstream delay is 4.4ms. The
ratio of these numbers is not equal to the ratio of the downstream and
upstream bitrates (which are 16544 kbit/s and 2056 kbit/s respectively).
So note also that the downstream delay is greater than the upstream
delay, although the downstream bitrate is higher.

HTH, Jan



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