AW: PMD data available
Dear all,
we also know this statistics of fiber PMD values. However, for us it is
unklear how representative these measurements are. I assume that with the
deployment of new fibers within the last few years the staistics shift to
lower PMD coefficients (ps/sqrt(km)).
Furthermore, our investigtions as well as the results of other groups show,
that the PMD limit of 10 percent of the bit period (corresponding to an
outage probability of well below 10^-6) only holds for tranmitterbandwidth
which are determined by the modulation. This means externally modulated
sources. In the case of directly modulated lasers with chirp so called
higher-order PMD distortions show up and reduce this limit (see references
in my New Orleans talk).
Regards
Henning
Henning Bülow (Buelow)
Alcatel Research Center
Alcatel SEL AG
Dept. ZFZ/ON
D-70430 Stuttgart
Germany
Tel.:+49 711 821-32283
Fax: -32457
-----Ursprüngliche Nachricht-----
Von: owner-stds-802-3-hssg-equal@xxxxxxxx
[mailto:owner-stds-802-3-hssg-equal@xxxxxxxx]Im Auftrag von Kolesar,
Paul F (Paul)
Gesendet am: Montag, 23. Oktober 2000 21:29
An: Equalization Ad-Hoc Reflector; 'Vipul Bhatt'
Betreff: PMD data available
A Bellcore paper by J. Peters, A. Dori, and F. Kapron from NFOEC'97 entitled
"BELLCORE'S FIBER MEASUREMENT AUDIT OF EXISTING CABLE PLANT FOR USE WITH
HIGH BANDWIDTH SYSTEMS" provides some field data about the PMD
characteristics.
I found a number of points relevant to the IEEE, which I will summarize here
rather than distribute the document. I am not sure that I can distribute it
to a wide audience due to possible copyright issues.
1. The data shows all of Bellcore's field data measured on the cable
plants of Bellcore's owners and other clients, both domestic and
international. Measurements began in 1995.
2. The data was gathered at 1550 nm using a commercially available
interferometric test set, principally on fiber paths in loop-back (a patch
cord connecting two fibers in the CO) so that the test set transmitter and
receiver could be placed from one end. At least 10 measurements were made on
each path over days of time to get changes over time. I gather that the
value of PMD Coefficient (ps/km^1/2) assigned to a path was the average of
these measurements.
3. The data is sorted by cable type, manufacturer, plant type (i.e.
aerial, buried, underground), and cable vintage. Although each shows
differentiation of PMD by the sorting parameter, the only sort that is
specifically defined is cable vintage. All others are anonymous so you can't
tell the actual cable type, manufacturer, or plant type.
4. About 35% of pre-1991 vintage cables show PMD > 1 ps/km^1/2. About
5% of post-1990 vintage cables show PMD > 1 ps/km^1/2.
5. A few interesting points on the cumulative distribution plot are:
50% of all fibers have PMD < 0.5 ps/km^1/2
80% of all fibers have PMD < 1.0 ps/km^1/2
90% of all fibers have PMD < 1.6 ps/km^1/2
6. The authors state that some organizations and standards bodies have
established 1/10 of the bit period is the maximum PMD that a system can
tolerate without experiencing a performance impairment. This statement
depends on several assumptions (not stated), but if it holds for 10GbE, then
40 km support should be possible on 90% of the existing plant using average
PMD measurements. Using worst-case PMD (defined as 3 x average), 40 km
support should be possible on 60% of the existing plant. These numbers are
over simplifications, and could change up or down depending on other factors
like cable type, manufacturer, vintage and plant type. These percentages
should have improved since the time of this report, as a greater percentage
of the installed plant would now be low-PMD.
7. Bellcore recommends considering PMD testing in the following
situations:
Deployment of 10 Gb/s on pre-1992 vintage plant (note the 1992 date
rather than the 1991 date implied by the data above),
Service upgrades scheduled for optical amplification,
Service upgrades that will eventually become 40 Gb/s systems.
I hope this information is helpful.
Regards,
Paul Kolesar
Lucent Technologies