On Mon, Nov 17, 2008 at 1:10 AM, Song Haibin <melodysong(_at_)huawei(_dot_)com>
wrote:
Bruce,
-----Original Message-----
From: p2psip-bounces(_at_)ietf(_dot_)org
[mailto:p2psip-bounces(_at_)ietf(_dot_)org] On Behalf Of
Bruce Lowekamp
Sent: Friday, November 14, 2008 3:44 AM
To: Das, Saumitra
Cc: p2psip(_at_)ietf(_dot_)org; ietf(_at_)ietf(_dot_)org
Subject: Re: [P2PSIP] P2PSIP diagnostics: PING discussion
Neither XP nor Mac OS X can be relied on to have accurate time sync,
although they in theory come with time syncing enabled by default.
Unfortunately, you just can't rely on synchronized clocks in all but
the most controlled of circumstances (and I think it's almost always a
poor idea, even then).
But one way delay (OWD) measurement is useful according to the motivations
in section 2.1 of RFC2679. It is also useful in P2P networks, e.g. when the
p2p network is used as a tunnel for data transfer. Clock synchronization is
hard for ordinary host, but that depends on what precision you want to
achieve.
Song,
No dispute that it's useful, it's just that what you need to do
anything useful with OWD is an order of magnitude beyond what you can
expect on any p2p overlay not specifically designed for measuring it.
In 2679, Section 3.5, 2nd bullet the requirement is described as
having a GPS receiver on each host or maybe each host being
synchronized directly with multiple gps-provided NTP servers, though
they didn't test whether that was good enough.
Bruce
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