 the idea of the MOXC was born in consequence of the bubble traffic forecasts, envisioning a high traffic in the backbone to require stratification of the optical cross connect to avoid huge and expensive OXCs. These forecasts are not realized in practice and the idea of the MOXC is almost aban- doned since currently there is no commercial MOXC. A particular discussion has to be done regarding the OADM. As a matter of fact, OADMs are the only wavelength routing equipment that are realized with pure optical techniques. While ADMs are a sort of small DXCs this is not true for OADM versus the OXC. Even if OADMs are mainly OCh layer elements, generally they are not realized by demultiplexing the WDM channels and switching them individually, but exploit specific optical technologies to extract/reinsert one or more channels without demultiplexing the whole comb. The OADMs can be divided into categories depending on the flexibility they have in choosing the channel to extract/reinsert. These categories are Fixed OADM: In this case the set of add/dropped channels is fixed and cannot be changed. Switchable OADMs: In this case the OADM has a certain number of Add/Drop ports, each of which is associated to one wavelength channel; the OADM can be configured to Add/Drop or to pass-through any of these wavelength channels while the channels that are not associated to one Add/Drop port can be only passed through. Tunable OADM: In this case the OADM has a certain number of Add/Drop ports and any wavelength channel can be Add/Dropped from any of the Add/Drop ports if the OADM is suitably configured. Any further discussion on OADMs cannot ignore the technology used to build them. Thus, we delay it to Chapter 7, in which the architecture and performances of network ele- ments devoted to route and switch information bearing frames or packets will be explicitly dealt with. Due to the fact that OTN is built on concepts similar to those applied for SDH/SONET, it is not surprising that automatic protection is embedded in OTN. Much like 