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Re: [ntpwg] I-D Action: draft-ietf-ntp-checksum-trailer-02.txt

Miroslav Lichvar <mlichvar@redhat.com> Mon, 07 September 2015 13:53 UTC

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Date: Mon, 07 Sep 2015 15:14:50 +0200
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Martin Burnicki <martin.burnicki@meinberg.de>
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Subject: Re: [ntpwg] I-D Action: draft-ietf-ntp-checksum-trailer-02.txt
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On Mon, Sep 07, 2015 at 10:23:41AM +0200, Martin Burnicki wrote:
> Greg Dowd wrote:
> >Probably moving further offtopic but why would you need 2?  And why
> >the counters?  The correction field in PTP was originally designed
> >because the hardware couldn't update the timestamps on the fly.  It
> >would post-process and then send a follow-up with the precise
> >timestamp.   NTP supports that  with the interleave mode.
> 
> IMO the interleave mode is just a hack.
> 
> "Interleaved mode can be used only in NTP symmetric and broadcast modes",
> quoted from
> https://www.eecis.udel.edu/~mills/ntp/html/xleave.html

Yeah, it would be nice if there was a proper "follow-up" extension
that an ordinary client could request from the server. There might be
a problem with traffic amplification, however. If the server is not
required to save the tx timestamp for a later query, there will have
to be two server packets per one client packet. Maybe a larger padding
in the client packet could be required to offset that.

-- 
Miroslav Lichvar
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