Subject: Re: [ippm] Synchonization state: consistency among owdp and ippm mib

From: stanislav shalunov <[email-masked]>
Date: 02 Aug 2002 03:47:09 -0400

"Henk Uijterwaal (RIPE-NCC)" <[email-masked]> writes:

> [...] I'd put a flag in the packet when it is sent indicating the
> status of the clock at the sender.  The packet is then received by
> the receiver, the receiver looks at its clock and tags the packet
> accordingly: both clock synchronized so a valid (delay) measurement,
> one or two clocks unsynchronized and a non-valid (delay)
> measurement.

There's a `synchronized' flag in each packet now and what you describe
is one way of using it.  (The receiver is supposed to store its own
timestamp with its own `synchronized' flag and the data user --
whoever it happens to be -- may choose to discard packets such that at
least one of the `synchronized' flags isn't set or it might treat
these packets differently or ignore the issue altogether.)

The question is -- I suppose -- about the following language in
draft-ietf-ippm-owdp-04.txt:

# if there is no notion of external synchronization for the time source
# (e.g., a cesium oscillator is used directly), the bit SHOULD be set.

Should this language be changed, in your opinion?  If so, how?

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/

A fool's brain digests philosophy into folly, science into superstition,
and art into pedantry.  Hence University education.       -- G. B. Shaw
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From: "Henk Uijterwaal (RIPE-NCC)" <[email-masked]>
Date: Fri, 2 Aug 2002 11:47:14 +0200 (CEST)

Stas,

> Should this language be changed, in your opinion?  If so, how?

I'd say "SHOULD NOT" and remove the "(e.g. a cesium ... directly)" as it
will be very confusing.

The issue is if 2 time-stamps from different devices can be be directly
compared.  That is not the case without some sort of synchronization to a
common source known to both devices.

It would perhaps be easier to call this bit "Synchronized to UTC".  While
you can do measurements without being sync'd to UTC, I'd think that one
will only do this in a lab environment, not in a network of distributed
measurement devices.

Henk

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That problem that we weren't having yesterday, is it better? (Big ISP NOC)

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---

From: stanislav shalunov <[email-masked]>
Date: 02 Aug 2002 10:20:36 -0400

> I'd say "SHOULD NOT" and remove the "(e.g. a cesium ... directly)" as it

Henk,

I agree.  Thanks for the text suggestion.  Is this what you wanted to
see?  It works for me.

diff -u -r1.39 draft-ietf-ippm-owdp.nroff
--- draft-ietf-ippm-owdp.nroff  24 Jul 2002 15:50:26 -0000      1.39
+++ draft-ietf-ippm-owdp.nroff  2 Aug 2002 14:17:21 -0000
@@ -979,13 +979,13 @@
 bits of the timestamp would be the same as the corresponding bits of
 NTP v3 timestamp).  The remaining octet specifies synchronization and
 precision.  The first bit is set if the party generating the timestamp has
-a clock that is synchronized to an external source (e.g., the
+a clock that is synchronized to UTC using an external source (e.g., the
 bit should be set if GPS hardware is used and it indicates that it has
 acquired current position and time or if NTP is used and it indicates
 that it has synchronized to an external source, which includes stratum
 0 source, etc.); if there is no notion of external synchronization for
-the time source (e.g., a cesium oscillator is used directly),
-the bit SHOULD be set.  The next bit is currently unused and may be
+the time source,
+the bit SHOULD NOT be set.  The next bit is currently unused and may be
 set to an arbitrary value.  The remaining six bits form an unsigned
 integer, which is the number of bits in the time-specifying main part
 of the timestamp that the party generating timestamp believes to be

Sex is the mathematics urge sublimated.                 -- M. C. Reed.
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From: "Henk Uijterwaal (RIPE-NCC)" <[email-masked]>
Date: Tue, 6 Aug 2002 11:22:03 +0200 (CEST)

> I agree.  Thanks for the text suggestion.  Is this what you wanted to

I think so, but can you send me the whole text.  I'm having trouble
applying this diff to the text ;-(

Henk