[ntp:questions] Win7: ntpd adjusting time backwards
david-taylor at blueyonder.co.uk.invalid
Sat Dec 22 14:57:17 UTC 2012
On 22/12/2012 14:36, Jan Ceuleers wrote:
> 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
Jan, yes, I appreciate that it's not the rate as such, I was really
trying to show how asymmetrical (10:1) the connection provided by my ISP
was. If they are trying to pack in as many customers as possible, who
knows what the actual backbone might be like? This is a cable modem
connection, by the way, and not ADSL.
I wonder how I could get the delay figures for my own modem? The only
data I can extract is: Latency: ~20 milliseconds, RTP jitter - up: 4
milliseconds, down: ~0.12 milliseconds.
Fascinating to see you have less delay on the slower upstream!
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