This paper presents a global methodology and optimization options for dimensioning the WDM optical layer in future transport networks. Several optimization processes are discussed and compared with results on the same study case, the European Optical Network. In particular, the results show the significant benefits of wavelength conversion and the advantages of "least number of hops" path routing among the various path routing strategies for wavelength channels. The connection rerouting optimization process, which requires a more algorithmic approach, is described along with the different criteria used to choose the optimized parameters (load on the link, fiber utilization ratio, etc.). The results on the European Optical Network case study illustrate that a global point of view should be adopted when optimizing these parameters as some processes can lead to worse dimensioning results.

The objective of this paper is to give an overview of the different studies we have performed at the research level regarding the design and implementation of a photonic wavelength division multiplexing (WDM) layer providing transparent transport services to client layers (SONET/SDH, ATM, etc.). Such a network requires a number of enabling factors to be assessed in order to become a reality. Among these factors are the availability of high-capacity WDM transmission systems and efficient optical routing nodes based on mature technology, the design of robust networks optimizing the utilization of resources, and the development of a management system in accordance with presently applied standards for transport networks. We review our achievements in these different fields.

Future optical networks will be operated with wavelength division multiplexing (WDM). Three different routing strategies for optical paths are presented here to perform allocation of resources (wavelengths) in WDM optical networks. Resource allocation has been studied with two different approaches, based respectively on wavelength routing and wavelength translation schemes. The implications of these routing strategies on WDM network dimensioning are explained and the results are illustrated on a European Optical Network test-case showing a major reduction of the number of needed fibres and pointing out the interest of wavelength translation.