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Abstract-Upgrading telecommunications access networks requires large investments in deploying new optical infrastructure, especially in terms of construction works and costs to reach the end-user, which seem only affordable in densely populated areas. By evaluating a cost-benefit analysis for the deployment of a Point-to-Point dark fiber infrastructure, this paper investigates how the economic risk of dark fiber deployment can be estimated and/or reduced in different settings. By applying the model on specific scenarios, which differ in area type, demand uptake and revenue scheme, it is concluded that the business case is only viable in a dense urban area with an aggressive takeup. In the other scenarios, the paper investigates possibilities and opportunities to improve the business case and hence decrease the investment risk. Examples of this improvement include prolonging the planning horizon, ensuring revenue from the start of the project by performing demand aggregation or examining where public funds might help.

Flexible optical networking can now be installed to increase network capacity in light of future traffic demands. This paper researches the different migration paths using a real option analysis, showing the impact of uncertainty.OCIS codes: (060.0060) Fiber optics and optical communications; (060.4250) Networks Future evolutions in telecom core networksWith estimated exponential core network traffic growths due to increasing access network traffic, future core networks will need to increase their capacity. The channel capacity will need to be increased beyond 100G per channel or higher, together with an increase of spectral efficiency. Additionally, the dynamic functionality of networks should be increased, allowing for dynamic re-optimization.To achieve the goals stated above, spectral flexibility -or flexgrid -has been identified as the key type of expected flexibility within dense wavelength division multiplexing (DWDM) systems. Present day DWDM systems operate under the Fixed Grid -or ITU grid. Multiplexers, optical network nodes and transponders are all tuned to this grid. The core network is based on IP offloading, transponders with fixed bit rate and modulation format. But traffic growth would require the use of several 10G or 40G channels between adjacent IP routers.Flexgrid, making the wavelength switched optical network (WSON) elastic by moving away from the ITU grid, can accommodate both sub-and super wavelength traffic. It allows an adjustable use of optical spectrum within a certain granularity. This granularity is the minimum bandwidth slot that can be switched in the optical spectrum (6.25 and 12.5 GHz are possible) [1]. This technology is slowly coming available, and operators have to decide whether or not to install this flexgrid capable equipment in their network. However, since this technology is still in its infancy, an installation today will be expensive or risk poor reliability. Additionally, the performance of this equipment might still be lacking the full functionality that may appear later.In order to make the correct investment decision, a techno-economic analysis is conducted for the future installations in the UK core network, as described in [2]. Additionally, it is indicated how uncertainty surrounding the future conditions, e.g. traffic growth and equipment prices, influences the optimal migration path. Since the operator has the opportunity to alter this path according to the future conditions, this analysis is well suited for a real option analysis (ROA) [3]. First, the different migration paths will be introduced and a standard techno-economic analysis will be performed. Secondly, the ROA will be conducted to indicate the importance of flexibility and how it influences the investment decision. Different future migration optionsThe need for flexgrid installations in the future core (and metro) networks will be mainly driven by the future traffic growth evolutions. Three different possible migration scenarios are described in Figure 1. In case of low traffic growth, th...