[time-nuts] NTP stratum 0

Magnus Danielson cfmd at bredband.net
Sat Jan 14 20:47:00 EST 2006

From: Bill Janssen <billj at ieee.org>
Subject: Re: [time-nuts] NTP stratum 0
Date: Sat, 14 Jan 2006 16:35:55 -0800
Message-ID: <43C998EB.2030605 at ieee.org>


> >>In Telecom Sync, Stratum 1, 2, 3 et al are internationally defined levels of
> >>frequency accuracy.
> >
> >Um, no. They are nationally specified in the USA. You find them in ANSI T1.101.
> >For their international variants you have to go to ETSI EN 300 462 series, as
> >well as the ITU-T Rec. G.810 to G.813. Neither the ETSI or ITU-T standards uses
> >Stratum indications, instead they use designations such as PRC, SSU and SEC.
> >
> Yes the T1.101 is a USA standard, but when it was finalized there was 
> international contributions and every
> attempt was made to harmonize the international standards and the USA 
> T1.101. I was active in the T1X3
> meetings.

I think you are missing the point. No question about from where the material
came, but I was commenting on the outcome and if you read the resulting
documents you will find that these terms did not make it into the international
standard, which was my point.

ETSI changes the specs for Stratum-3/SEC clocks and Stratum-2/SSU clocks to
match the needs for the European PDH and SDH needs. That is the "2048 kHz
based" networks also known as "Option I SDH" where as the ANSI specs for the
clocks is in the "1544 kHz based" networks also known as "Option II SDH" (There
is also an "Option III SDH" but lets just leave that in obscurity shall we?
It's 64 kHz based.). The ITU-T Rec. G.781 only uses the Stratum 2, 3 and 3E
terms to reference to SONET clocks but their specs is refered to as G.812
Type II, III and IV. After the introduction, they are only refered to as
QL-ST2, QL-ST3E and QL-ST3 (in falling quality order). Thus, they are refered
to but not the primary term.

The Stratum 3E (Stratum 3 Enhanced) and Stratum 4E (Stratum 4 Enhanced)
indicates that it is not good to try to assign a strict number series of
integers since you might need to insert something into the series and they did.
Ah well.

So, the use of Stratum for clock quality is something out of the Bellcore (now
Telcordia) and ANSI specs. Also, in these they not only use Stratum. The SMC
(SONET Minimum Clock) is added in ANSI T1.105.09 and the TNC (Transit Node
Clock) is added in ANSI T1.101 (Annex A).

So, trying to get a common picture by combing the Stratum numbers from T1.101
and from RFC 1305 will just result in computation error.

We are thankfull for the T1X3 committe and the work done there, but what popped
out on the other end of ETSI and ITU-T is a bit different, that is all I'm


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