Deepak Jain writes: [a response with excellent pieces of advice on CWDM vs. DWDM.]

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

Yes. What we often do is buy a single pair of fiber (which happens to be the smallest amount you can get) and use a bi-directional optical system (CWDM or DWDM). So we have one of the two fibers free for a later upgrade (or another useful purpose). [...]

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

An excellent management summary of CWDM vs. DWDM :-) -- Simon.

Fletcher, My primary responsibility here is engineering exactly these kinds of systems. 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:

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Nanogers,

We are looking for advice/experience from folks who has used small 6-8 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.

Arman,

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 it) you can stay on the CWDM side. The lasers and the gear is generally cheaper.

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 all-optical amplification and such are not necessary. I am not aware of any all-optical CWDM amplifiers yet. (for example).

If you are planning more than just 1 DF run, you could buy the less 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 al 8 waves x 1G or 8 x 2.5G (full duplex). Some DWDM gear will let you double 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.

thanks, fletcher