"Kevin Oberman" <[email protected]> wrote in message
news:[email protected]...
From: "David J Taylor" <[email protected]>
Date: Fri, 22 Oct 2010 20:43:01 +0100
Sender: [email protected]
"Evandro Menezes" <[email protected]> wrote in message
news:f13f950a-3168-4a11-ba09-f4d225e7b...@t13g2000yqm.googlegroups.com...
> On Oct 22, 10:23 am, "David J Taylor" <david-
> [email protected]> 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
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