Merits of low-density WDM line systems for long-haul networks

Conventional wisdom claims that the higher the number of wavelengths supported by a dense wavelength-division multiplexing transmission system´s line system the better, since the high costs of amplifiers are split among more revenue-generating entities. For example, a 20λ link must cost less than 25% of the cost of an 80λ link to compete at full (80λ) fill, assuming four 20λ links need to be deployed in parallel. We show that this is not necessarily the case if network considerations and technology evolution are taken into account. In particular, we show that a 20λ link can cost as high as 64-79% of the cost of an 80λ link and still be competitive at full fill, while providing much lower initial cost. This is because of the cost reduction of technology over time, economic considerations (net present value), nonuniform capacity needs in real networks, and how network maintenance can be achieved. We also reason why such lower end systems can indeed achieve the required cost reduction.