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RE: IEEE 802.3 Requirements


The 62.5 um fibers have been used for over 15 or 20 years.  However, we just
started paying attention to the DMD fibers two years ago.  Because of the
small DMD population, industry did not paying attention to it.  In fact, the
DMD fibers have been with us since the graded index fibers were introduced.
DMD fibers are defected parts like any other products having defected parts.

In the past, the MM fibers, particularly 62.5 fibers, were only used with
LED sources over-filing the fibers, which is hardly capable of creating a
DMD results except low bandwidth.  It was until GbE requiring laser over
62.5 um fiber, the DMD has not been identified as a detrimental problem.   

The fiber vendors do not characterize "DMD" as one of the parameters in
their commercial specification due to its very small, negligible population.
As a result, no one really pays attention to verify it, unless an
experienced engineer is purposely looking for DMD fibers.  Some time, just
to identify DMD fibers from the waveforms is not a simple job. 

Ed Chang
Unisys Corporation

----Original Message-----
From: Bruce_Tolley@xxxxxxxx [mailto:Bruce_Tolley@xxxxxxxx]
Sent: Friday, May 14, 1999 5:29 PM
To: Chang, Edward S
Cc: Thomas Dineen; stds-802-3-hssg@xxxxxxxxxxxxxxxxxx
Subject: RE: IEEE 802.3 Requirements

As far as I know, hardly any "DMD fibers" have been identified to date.