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How to choose the right 40G/100G+ coherent systems to maximize CAPEX savings

Selecting the right dispersion compensation level on coherent links is not an option, not in a competitive landscape where services keep multiplying and expectations for quality of experience keep soaring towards new heights. Paradoxically, the budgets earmarked for capital expenditures (CAPEX) remain just as tight. Your field teams installing, monitoring and troubleshooting high-speed networks have to deal with this given. But what if you were overspending without knowing it?

What if you could trim your expenses without compromising performance? Our recent observations in the field suggest that service providers are sometimes overspending when it comes to coherent detection systems. Why? Simply put, because they are paying for a level of performance that is occasionally unnecessary for dispersion compensation in coherent networks with transmission rates of 40G or 100G and above.

The reason this is happening is because network equipment manufacturers (NEMs) or network solution vendors (NSVs) currently offer different models for their coherent detectors, and they come with different dispersion compensation levels for chromatic dispersion (CD) and polarization mode dispersion (PMD):

  1. Low dispersion compensation performance at a lower cost, mainly for metro networks
  2. High CD/PMD compensation for a higher cost, mainly for long-haul or ultra-long-haul networks

In between these lower and upper ends, other dispersion compensation levels exist.

Though NEMs and NSVs are very secretive about their dispersion compensation performance, some generic data is available on the market: 

Dispersion compensation performance

As we can see from the table above, the performance varies greatly between models – sometimes even by a factor of 10 for CD.

As a service provider, if you are unaware of the link’s fiber dispersion properties, you run the risk of overspending when acquiring a coherent system, if you choose the high-end model to have a cushion while the mid-range or low-end model might have worked instead.

How to avoid spending more than you should? Simply follow these steps:

  1. Measure the fiber properties (CD and PMD) of the link(s) with a dispersion tester.
  2. Ask your system vendor for the various dispersion compensation levels offered in their portfolio.
  3. Pick the coherent system offering the right dispersion compensation capacity, thus saving CAPEX.

By buying just the performance you need, it is possible to score valuable CAPEX savings, because you will use a low-end or mid-range coherent system for the fibers with high dispersion, and select a high-end, more expensive coherent system only for the fibers that truly need that higher level of dispersion compensation.

Would you like more detailed information on this topic? Talk to an expert today on how to optimize your CAPEX savings when it comes to dispersion testing.