[ntp:questions] Win7: ntpd adjusting time backwards
snews at lordynet.org
Sat Dec 22 17:49:31 UTC 2012
David Taylor wrote:
> 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!
My own usage is more like 15:1 down:up so my 13:1.2 Mbps down:up
data rates seem to fit quite well.
When on 2 Mbps I had problems with very high latency on uploads
and implemented altq traffic shaping which increased my maximum
upload speed from around 150 kbps to around 250 kbps. There is
also higher priority for icmp, dns and ntp.
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