Le 26 mars 2014 à 14:52, Brian Utterback a écrit :
> On 3/26/2014 8:00 AM, mike cook wrote:
>> Le 26 mars 2014 à 12:09, Coiso22 a écrit :
>>
>>> Hi all,
>>>
>>> I am trying to synchronise the time of an Android device with a local
>>> machine, for test purposes, using ntp. However, the difference between the
>>> time of the device and the ntp server is always around 5 milliseconds.
<snip>
>> electron:~ mike$ ntpq -pn
>> remote refid st t when poll reach delay offset
>> jitter
>> ==============================================================================
>> *192.168.1.4 .PPS1. 1 u 20 64 377 1.600 0.131
>> 14.759
>>
>> As you can see the delay and jitter (which is very variable ) go up, but the
>> offset stays < 1ms. So it should be possible for you to do better.
>> If you have another non Android wifi client on your net, what do you see
>> with that as a client?
>
> Mike, what makes you think that this is any more accurate than it was before?
> It surely is the case that NTP thinks that it has less offset, but with a
> jitter value that high is it almost certainly wrong about that, but it has no
> way to know what the real value is, so it displays only what the latest
> calculated offset of the moment was. Essentially you went from an offset of
> -0.284+/-0.037 to an offset of 0.131+/-14.759 I don't think that is an
> improvement.
>
You are right of course. I just picked the last of my samples which happened to
be the worst. 10 mins later we were back at
electron:~ mike$ ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
*192.168.1.4 .PPS1. 1 u 50 64 377 1.586 0.031 1.226
with the jitter figures in the >1< 2ms bucket. I was just pointing out that <
5ms looks doable.
That said and in line with your comments, the variability of the jitter over
wifi does make sub-ms accuracy questionable.
> Brian Utterback
>
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