Dark Fiber: CWDM vs. DWDM

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August 17th, 2012 at 13:26
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As we talked about recently, using Dark Fiber can be a very affordable way to get cheap, scalable network transport capacity. When ‘lighting’ a dark fiber network, there a few primary design considerations to consider. In particular, is the kind of WDM system to use is very important, as it drives your cost and scalability.


CWDM: Scales to 18 distinct channels. Until recently, CWDM optics only scaled to 2.5Gbps per wave length, but some manufacturers have released 10Gbps SFP+/XFP optics. The primary advantage to using CWDM is that 1Gbps optics are very inexpensive — under $150 per optic for a range up to 80km. 120km optics are available, but carry a higher price premium. 10Gbps optics are available, but limited to 40km and can be purchased for under$2,000 per optic.

DWDM: Scales up to 80 channels (or more), allowing for vastly more expansion than a CWDM system. 1Gbps optics are expensive, however, costing about $1,000 for a 80km optic. 10Gbp optics generally cost the same as CWDM optics or about $2,000/ea. Additionally, some manufacturers offer tunable DWDM optics. Tunable optics are fairly costly at $6,000/ea, but offer the advantage of being able to deploy the same SKU and use it on any DWDM channel.

Hybrid CWDM/DWDM: It is also possible to run a hybrid CWDM/DWDM system.  By not utilizing the 1530 and 1550 nm CWDM channels, you can insert DWDM waves into your existing CWDM network.  Thus, you can start with a cheaper CWDM network and then add DWDM on at a later date.

Ultimately, the choice to use CWDM or DWDM is going to be driven by the number of wavelegnths needed, the speeds needed and the future growth projections.  If you only need a handful of waves and are using 1Gbps optics, CWDM is the way to go.  If you need dozens of waves, 10Gbps speeds, DWDM is the only option.