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Patch cord for 1300 WWDM


There seems to have been some confusion at the La Jolla
meeting over the necessity for an offset patch cord for
1300 nm WWDM.  Because of this, and additional comments  
made on the reflector since the meeting, I am writing
this email to clarify the situation.

Fact 1. An offset patch cord is NOT required for 1300 nm
WWDM in order to meet the current MMF objectives of 802.3ae.
That is to say, it is NOT required in order to achieve a 100       
meter link length on the installed base (this includes both
62.5 and 50 um standard MMF, which both have a 500 MHz-km OFL
bandwidth length product at 1300 nm), NOR is it requred to
achieve a 300 meter link length on the new enhanced BW 
MMF, which also has a 500 MHz-km OFL bandwidth at 1300 nm.

Needless to say (but I will for the sake of completeness)
1300 nm WWDM also supports single mode fiber up to 10 km,
again without a patch cord.

Fact 2.  The ONLY time you need to use a patch cord with
1300 nm WWDM is if:

1. You want to extend the link length of the MMF installed base
to 300 meters


2. The fiber in question is "DMD challenged".

Please note that if you are in this particular situation, none
of the 850 nm based PMDs will satisfy your need, patch cord or
not (but see Note below).  Your only alternative in this situation,
with an 850 nm PMD, is to install new fiber, either the enhanced BW
multimode fiber or single mode fiber.  Therefore, the notion that
the patch cord is some sort of "penalty" you pay for using 1300 nm
WWDM is really the wrong way to think about it.  Rather than a
shortcoming, it is actually a benefit, since it gives you the (rel-
atively speaking) low cost option of using a patch cord in a sit-
uation where your only other alternative is to pull new fiber.

Note: The 850 nm 4 channel CWDM PMD will allow you a 300 meter link
length, without a patch cord, on the installed base of 50 um fiber
ONLY.  However, this is a small benefit, since the great majority
of the MMF installed base is 62.5 um fiber, on which 850 nm CWDM 
will only support a 100 meter link length (due to the fact that 
62.5 um fiber has an OFL bandwidth length product of only 160 
MHz-km at 850 nm). 

David Dolfi
Agilent Technologies