RE: SJTP: Minutes from 08-May meeting
Piers-
At 05:59 PM 5/10/01 +0200, DAWE,PIERS (A-England,ex1) wrote:
Ben,
Your slide set says "Motivations - Why not use the 1+x28+x31
PRBS?". This
was useful because it helped clarify the issue of what we are trying to
do.
The question I have been trying to bring before the group is not that,
but
"Why wouldn't we measure (a DUT) in its normal mode of
operation?" And the
arguments I have heard are basically for convenience, not for
interoperability.
I looked at SONET (GR-235) and didn't find anything relevant about
test
patterns. ITU-T's policy, I believe, is to restrict itself to
specifying
the behaviour of the normal mode of operation at the available
(optical)
ports only; a "black box" specification. Presumably SONET
systems are
tested with SONET frames running: loaded with what?
empty?
There is a radically different concept in the telcom
world."Circuits" are installed, debugged and then "turned
up" (presumably by technicians at each end who are talking to each
other other over the Order Wire). this includes setting the transmission
contents to a known state. That is, there is a specific maintenance mode
which is intended for testing in place. Ethernet has never had any such
notion. The current discussion of a mode for bench testing is still a
long way away.
Another one of the underlying assumption in that tradition that I don't
think we can take for granted is that a single owner has physical access
to the PHY at each end of the media. Ergo the requests that we have heard
for OA&M.
Geoff
doesn't matter?
I guess it may be "can't matter", so that networks can be
tested remote from
the terminal concerned (which may be owned by a different
operator). It's a
feature of our line code, even more than SONET carrying speech, that
traffic
and idle/LF/RF all appear on the wire like random data with very
predictable
statistics, so testing with any of these will give the same results,
with
very predictable statistics or error bars.
More comments on slide 2:
"Use existing logic (1+x39+x58 scrambler)" and "One that
is easy to
generate" should be grouped together.
"Find a robust test pattern" Does this mean
anything?
Slide 3:
Tests requiring the Jitter Pattern
Not "requiring". We decided that eye mask didn't and we
are debating the
others. Could you say "Tests with mixed frequency
pattern"? Then
elsewhere, when presenting "two seeds" say that one seed is to
emphasise the
unlikely, the other is to represent the typical.
Rise/Fall Time measurement is in OFSTP-4A: "Unless otherwise
specified in
any product-specific documentation, a 2^23-1 PRBS pattern is
recommended."
This is the same standard as defines eye measurement. As we
discussed in
that context, a pattern which does not emphasise the unlikely would
give
fewer rogue measurements.
Return loss can be done with the optics switched off: no pattern.
RIN is a two part measurement: modulated and not. We haven't
specified any
pattern, probably "Either way" is the right category for
now.
Slide 7:
Second thoughts on "Ability to generate and check the pattern in the
same
device at the same time". This wouldn't apply to a jitter
measurement which
is either tester -> DUT or DUT -> tester, and probably not to a
sensitivity
measurement for the same reason. It might be nice for a field test
of link
margin, but you could do that with test packets and CRC checks
anyway. When
else would you be looking at DUT -> DUT, whether loopback or between
two
modules?
I am looking through D3.0 to see what we have written down, after
several
discussions and reviews, for each of the optical tests. It's quite
varied
and I hope to report more later, but you wanted feedback today.
Thank you,
Piers
> -----Original Message-----
> From: Ben Brown
[mailto:bbrown@xxxxxxxx]
> Sent: 08 May 2001 21:19
> To: serialpmd
> Subject: SJTP: Minutes from 08-May meeting
>
>
> All,
>
> Thanks for your participation. Attached are the minutes from
> today's conference call. Also, attached is an updated copy of
> the presentation. Please review before Thursday evening as I
> intend to make it available to the task force at that time.
>
> Thanks,
> Ben
>
> --
> -----------------------------------------
> Benjamin Brown
> AMCC
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> Suite 104
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>