🚀 go-pugleaf

In article <1992Jul29.161817.2757@ncar.ucar.edu>, hyder@niwot.scd.ucar.edu (Paul Hyder) writes:
|>After three months tracking down a problem with a fiber based Ethernet
|>that ended up being overdriven fiber connections I'd like to get some
|>feedback from anyone out there that has or is planning configurations
|>similar to ours.
|>
|>This new network used fiber as the major interconnect in preparation for
|>full scale FDDI and beyond implementation.  Details on request (were
|>posted in comp.dcom.lans.ethernet), in short we used short fiber runs
|>(3 to 300ft) to connect between close buildings, between floors, and to
|>in-room hardware.  We have been seriously impacted by the lack of
|>published minimum loss/length requriements.  (Overdriven fiber is truly
|>a nasty debugging chore.)
|>
|>QUESTIONS:
|>	1.  Has anyone seen overdriven FDDI?  Is there a minimum
|>	    loss/length requirement?
|>
|>	2.  If you have short fiber optic runs that had overdrive noise
|>	    how did you solve the problems?  Where did you get
|>	    attenuators? What did your solution cost?
|>
|>As always TIA.  Email to me please.
|>	Paul Hyder
|>	NCAR
|>	Boulder, CO

The transmitter, receiver, and fiber specs are spelled out in detail in
the two FDDI PMD standards (multimode and singlemode).

In the multimode case, the max transmit power is within the receiver specs,
so there is  no minimum loss when using standard (62.5 micrometer) fiber.
I've been told that there MAY be problems (depending on transceiver) if you
use 100 micrometer fiber.  See the appendix on alternate fiber sizes in the
multimode PMD standard for more detail, but you might want to use a power
meter to check such configurations.  Better yet, use conventional size
fiber.

In the singlemode case, there are two classes of transceivers.  One is intended
for moderate distances, the other for long distances.  The long distance
version definitely DOES have a minimum loss requirement (on the order of 10 dB,
but check the individual product since there may be some small variations
among transceivers from different suppliers).  If you plan single mode
installations with significant cable lengths, you should do the appropriate
planning and measurement to get signal levels right.  Given the cost of
such installations, the additional cost of doing a thorough job is trivial.

	paul