This paper deals with the topological design of a next generation optical network that provides fully meshed connectivity between electronic edge nodes. Such an architecture, nicknamed "PetaWeb", is simple to manage and offers a total capacity of several petabits per second. From the topology standpoint, the PetaWeb presents a very unusual structure as the backbone nodes are totally disconnected. In this paper, we present for the first time a formal mathematical formulation of the network design problem involved in a PetaWeb deployment. We also want to assess the different design parameters of interest in the design of the PetaWeb. Computational results will be presented and discussed.