AW: Test patterns ?
Hi,
The most recent text for Extinction ration measurement is contained in G.691
as last SDH/ Sonet standard and in the same wayG.959.1.
Please note that no particular pattern is defined. What means the
measurement should be possible at any signal compliant:
The text reads:
Extinction ratio
The minimum admitted value of the extinction ratio (EX) is defined as:
EX=10*Log10(A/B)
In the above definition of EX, A is the average optical power level at the
centre of a logical "1" and B is the average optical power level at the
centre of a logical "0". The convention adopted for optical logic levels is:
emission of light for a logical "1"
no emission for a logical "0"
Note that you can synchronize to some bits due to the unscrambled first row
of Sonet OH (Frame sync is done there) Here however the measurement has to
use the average of the bit centers what means also bits not located in this
part of the frame.
It should be noted that any method employing particular patterns would first
require to manage the test pattern generation and secondly generate results
different to real life traffic.
So I am in favor of the ITU approach.
Regards Juergen
----------
Von: DAWE,PIERS (A-England,ex1) [SMTP:piers_dawe@xxxxxxxxxxx]
Gesendet: Dienstag, 2. Januar 2001 16:35
An: 'Serial PMD Ad Hoc Reflector'
Betreff: RE: Test patterns ?
The pattern for extinction ratio and OMA measurements should have
the
following characteristics:
Convenient to generate, e.g.:
Real traffic
Idling
Something synchronous to the ICs:
66 bit word oriented?
Byte oriented?
Convenient to measure
Static pattern?
Gives sufficient accuracy
Depends what we want to measure...
Acceptable measurement time
There are at least three competing philosophies on what we want to
measure:
1. We are trying to find the "1" and "0" levels well away from
the
transients (as in GigE)
2. We may as well measure the average "1" and "0" levels. Then
we can
measure in or near service. This is ITU-T's approach.
3. It is of little interest to the customer that some bits are
better
than others. Just measure the eye opening, including the isolated
bits.
While the GigE is 10 bit word oriented, 5x"1" + 5x"0" makes sense in
that
scenario; criterion easy to generate. Not for either 10GE serial
line code.
The amplitude measurements under philosophy 1 are not intended to
stress
anything to do with long run lengths. 3,4,8,or even 66 x"1" then
x"0" would
probably work for this test, even though the transition densities
are far or
very far from normal. I doubt if there is need for a hard "shall"
to define
the pattern.
Piers
> -----Original Message-----
> From: Rich Taborek [mailto:rtaborek@xxxxxxxxxxxxx]
> Sent: 27 December 2000 08:55
> To: 'Serial PMD Ad Hoc Reflector'
> Subject: Re: Test patterns ?
>
> Peter,
>
> Just some "food for thought comments":
>
> Öhlén Peter wrote:
> >
> > We need a few test patterns for serial PMDs, and I think it
> would be good to
> > start listing the different measurements which need
> specific patterns, and
> > what kind of patterns that would be good to use. In 1GbE 5
> different test
> > patterns seem to be defined, and a few of them are based on
> 8b/10b code
> > groups which I don't think is a good idea for 10G serial PMDs.
>
> > 1. For extinction ratio and OMA measurements I think a
> repeating "11110000"
> > pattern (4x"1" + 4x"0") would be a good idea. (Better than
> 5x"1" + 5x"0" as
> > in 1G.)
>
> For 8B/10B, the extreme maximum run length is 5 and the
> typical maximum
> run length is 4. For 64B/66B, the extreme maximum run length is 66
and
> the typical maximum run length is >>4. Since 64B/66B is
> employed for all
> 10G serial PMDs, why would a repeating "11110000" pattern,
> equivalent to
> a 1.25 GHz square wave, be "a good idea" for extinction ratio and
OMA
> measurements? Why would it be any better than a "1111100000"
> pattern? Is
> it representative in any way of the very wide dynamic range of
64B/66B
> signaling (relative to the narrow dynamic range of 8B/10B)?
>