 components. On the other hand, the transparent network architecture has all the problems of a com- pletely analog layer. This problem was clear since the beginning of the use of optics for transmission, and from that moment, a revolutionary solution was proposed: let us devise digital optics. The idea is to completely change the network architecture by eliminating the time divi- sion multiplexing (TDM) physical layer based on circuit switching substituting it with a packet switched optical network based on packet switching optical machines. These optical routers have to deal directly with some sort of optical burst or packet at a very high speed, performing all the operations that are needed to store and forward them. Such a deep revolution in the network could use a suitable form of GMPLS, due to the flexibility of this control plane, and could also incorporate into the optical routers higher layer electronics functions depending on the definition of the relation between the optical bursts or packets and the traditional IP and Ethernet protocol stacks. At the state of the art, however, the key point of this solution is not the network architec- ture, but the optical technology allowing digital functions like storing, header recognition Next Generation Networking: Enabling Technologies, Architectures, and Performances and elaboration, and SO on, to be performed. A huge amount of research has been devoted to this solution, both from technology and networking points of view. Naturally, several variations have been proposed for all the alternatives we have listed, and even among the proposers of one of the three solutions, there is no complete consen- sus on how it should be implemented. In this chapter, we will review the basics of the three network architectures we have introduced, both from technology and networking points of view. It will be naturally impossible to detail all the different variations in which a particular idea has been proposed, but we will try to make clear the advantages and disadvantages of 