ode 3. This operation is called grooming and consists essentially of using the switching capa- bility at a higher layer (in this case the MPLS layer) in order to exploit at best the transmis- sion capacity installed in the field. In this case, exploiting the grooming capability of the LSR in node 4 allows a wavelength to be spared on the link from 4 to 3, at the cost of eight LSR ports in node 4. Naturally, more complex network algorithms can be devised to decide if grooming has to be performed in a certain node or not SO to achieve a global network optimization. The equation providing the network cost if this second design criterion used is (8.2) As anticipated, this is again a linear expression of the design parameters and Eh,k if the integer part is neglected. 8.4.1.1.3 Design with a Routing Hub Looking at the topology, it is possible to note that two nodes, namely nodes 2 and 4, are connected with all the other nodes. This characteristic can be exploited for a particular type of design where all the nodes originating an GLSP create a connection with the hub and then the hub distributes the GLSPs to the destinations. This design neither achieves minimum cost of nodes nor minimum cost of links, but it can be useful in cases in which the overall cost is almost equally shared between links and nodes. Moreover, several times, there are also other design objectives besides the cost minimi- zation. For example, in the case of the presence of a hub, since all the GLSPs pass there, authentication and QoS are easier to manage. In our example, let us set the hub in node 4. Thus all the GLSPs are sent to node 4 with a single hop connection and node 4 distributes the GLSPs to the destinations. Grooming generally is required at the hub to save wavelength at the hub exit. In our case, MPLS LSPs that from nodes 1, 4, and 2 are directed toward node 3 can be statistically multiplexed together in a single wavelength between nodes 4 and 3. The overall number of LSR ports is in our case is , = 48, the number of OXC ports is , = 1