[ntp:questions] What level of timesynch error is typical on WinXP?

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sat Oct 23 08:09:40 UTC 2010


"Kevin Oberman" <oberman at es.net> wrote in message 
news:20101022203504.B5BA51CC3E at ptavv.es.net...
>> From: "David J Taylor" <david-taylor at blueyonder.co.uk.invalid>
>> Date: Fri, 22 Oct 2010 20:43:01 +0100
>> Sender: questions-bounces+oberman=es.net at lists.ntp.org
>>
>>
>> "Evandro Menezes" <evandro at mailinator.com> wrote in message
>> news:f13f950a-3168-4a11-ba09-f4d225e7b6b1 at t13g2000yqm.googlegroups.com...
>> > On Oct 22, 10:23 am, "David J Taylor" <david-
>> > tay... at blueyonder.co.uk.invalid> wrote:
>> >> That could explain why I see higher NTP jitter on a Windows system
>> >> running
>> >> a USB network source (digital video data stream) than receiving a
>> >> similar
>> >> data stream on a PCI card under either Windows XP or Windows-7.
>> >
>> > Possibly, but USB, as a polled, token-ring like protocol, will always
>> > add jitters in this case.
>>
>> Thanks.  I don't understand enough about USB - do you have good 
>> reference?
>
> For a good into, read the Wikipedia article:
> http://en.wikipedia.org/wiki/Universal_Serial_Bus
> -- 
> R. Kevin Oberman, Network Engineer

Thanks fir that pointer, Kevin.  It's one I've used before.

I had mis-understood your comment to mean that data transfers on USB were 
polled, and not interrupt driven, however I am not sure whether that was 
what you meant to imply.

With the particular PC in question, the issue appears to be that with the 
high-bandwidth (peaks of 20-25Mb/s, average 10Mb/s) USB device running and 
it support software operating, the NTP software shows much higher offset 
values than are typical for a LAN-synched Windows system.  It may be that 
the LAN packets are getting delayed by the DVB (digital video broadcast, 
actually data) stream.

Cheers,
David 




More information about the questions mailing list