[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.


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