portance for carriers. For a general comparison as that we are targeting now, using computationally heavy algorithms specific for a particular technology would not be the right choice. Different algorithms can introduce different levels of errors in the final solution and comparing results coming from network simulations adopting different algorithms is always com- plex requiring a preliminary assessment of the algorithms performance working on cases whose solution is known. Telecommunication Networks Thus, we will base our analysis on a single simulator sufficiently rich to simulate with a good accuracy complex multilayer networks. The principles of the multilayer simulator working are detailed in Ref. [70]. The algorithm is based on the bare definition of a multilayer network, which is on the client server relationship between adjacent layers. In particular, the highest layer is assumed to receive a traffic demand from its client, the algorithm determines the resources that this layer needs to carry out to satisfy these requests in terms of needed switching/routing hardware and transmission capacity. Since the traffic request will be accompanied by a QoS requirement, it has to be taken into account in dimensioning the layer. Moreover, every layer specific equipment has to be represented by a detailed physical model that, among other things, represents the scal- ability of the equipment via the addition of new cards or similar procedures. While switching/routing requests drive the design of the specific layer equipment, the traffic requests are passed at the lower layer that see them as client requests and start again the dimensioning. The iterative procedure stops at the bottom layer, where transmission resources drive the design of the transmission WDM systems. In order to design the adjacent layer, the layer topology has to be known (nodes cannot be added or subtracted during simulation). When the physical layer is SDH/SONET or OTN, it can be designed either as a mesh or as a multiring network. In the mesh ca