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Re: Advice/Experience with small sized DDWM gear
From: "N. Richard Solis" <nrsolis () aol net>
Date: Thu, 7 Aug 2003 17:14:58 -0400


My primary responsibility here is engineering exactly these kinds of 

The biggest difference between CWDM systems and DWDM systems is system 
reach.  Most CWDM systems are designed for short haul applications like 
yours (approx 20km and under.  Most DWDM systems are designed for much 
more expansive requirements (50-600km).  The primary reason for this is 
amplification and laser power.  CWDM systems use low power uncooled 
lasers that can drift in frequency making it hard for them to pack many 
channels into the limited transmission window provided by available 
fiber.  Amplifiers will raise the system cost.  DWDM systems use higher 
power lasers that are actively cooled to make them stable in frequency 
and consequently, you can fit more into the transmission window.  They 
get system reach by using optical amplifiers.

I've had great experience with several vendors but ultimately your 
choice depends on your particular situation and requirements.  CWDM will 
be much lower cost.  Look at the ONLINE 2500 series from Ciena or the 
CWDM options from Movaz Networks.  But don't stop there.  There are MANY 
other CWDM vendors that can help you.

Don't forget to check what kinds of channel bandwidths are supported. 
Some can provide actual BER information for each muxed channel.

If you have further questions, don't hesitate to contact me.

fkittred () gwi net wrote:

On Fri, 20 Jun 2003 14:56:41 -0400  "Deepak Jain" wrote:

We are looking for advice/experience from folks who has used small
Wavelength DDWM.

Also what are the pros and cons of CDWM and DDWM?

Application;  5 Mile Dark Fiber between two carrier neutral hotels
in SF.

All help is appreciated and results will be shared if requested.


      I think the biggest difference between small DWDM and CWDM is
how much
growth room you need.

      If you need 8 wavelengths (possibly 16 is still called CWDM
but I doubt
you can stay on the CWDM side. The lasers and the gear is generally

      With DWDM gear everything seems to be more expensive, but you
get a lot
more control as the electronics governing the chassis' tend to be
much more
advanced. On a short run like that, many advanced features like
amplification and such are not necessary. I am not aware of any
CWDM amplifiers yet. (for example).

      If you are planning more than just 1 DF run, you could buy the
expensive solution and just swap it out when you need something more
and use
the CWDM solution somewhere else.

      If you have decent/modern fiber, you should be able to
comfortable sign
8 waves x 1G or 8 x 2.5G (full duplex). Some DWDM gear will let you
that on just 8 colors by going full duplex on each fiber (each thread).

      So its a question of how much BW you need and how much you
want to pay
for right now.

      (If I am wrong, someone please correct me).

Hope this helps, let me know what you decide.

I would be interested in recommendations for specific hardware.  We
are looking at longer runs and the units must be NEBS compliant as the
nodes are in telco COs.


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