modular when adding at its input a new fiber, with its whole WDM comb, it can be scaled to accept the new input simply adding other parts, without the need of changing sometimes what is already deployed. The same OXC fabric is wavelength modular if, adding a wavelength to a set of input WDM combs (from one to all), it can be scaled to accept the new input simply adding other parts, without the need of changing sometimes what is already deployed. Telecommunication Networks On the contrary, since an OXC switch fabric performs essentially an OCh layer func- tion, asking if it is label switched path (LSP) modular has no meaning since LSPs are not discriminated by the OXC. Requiring the LSP modularity is correct for the switch fabric of an IP router in the case that it works as a label switched router (LSR). A last element that determines the performances of a switch fabric is its robustness in front of an internal failure [12]. Naturally, the possibility of rerouting connections affected by an internal failure is based on the availability of alternative disjoined routes, and it is well possible that the needed rearrangement of a switch fabric due to a failure will transform it from strictly nonblock- ing to blocking, for example. To summarize, the main qualitative elements allowing the evaluation of the perfor- mance of a switch fabric are as follows: Blocking characteristics with unicast traffic Blocking characteristics with multicast traffic Static applications Ability to switch correctly after a long inactive period Ability to remain in a status without power feed Dynamic application Power consumption Real estate Modularity at every lower layer Capability to preserve connections in front of internal failures Besides these qualitative elements, a switch fabric can be characterized by its throughput characteristics. When a traffic level is offered at the switch fabric ports, for example, a cer- tain input packets process characterized by its mean number of packets per second, the output traffic follows the input one