RE: SJTP: Minutes from 08-May meeting
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? 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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