I Introduction
The concept of optical networking has undergone a deep revision in past years, modifying and extending the basic layout which is simply based on the presence of fibers in the physical transmission layers. The bandwidth of a single-mode fiber exceeds by orders of magnitude the requirements of the most demanding peer-to-peer producer/consumer pair. In order to avoid wasting fiber resources and to fully utilize the costly electronics that drives them, the physical channel can be shared among many tributary streams.