 the ITU-T automatically switched optical network (ASON) standard, where the mechanisms of wavelength aggregation needed to accommodate the use of PICs in the network are similarly not completely foreseen. In the case of ASON, that is not a complete protocol suite, but quite a detailed network architecture, probably the needed work is easier and could be included in the ITU-T con- tinuous work for the update of the standards. 10.2.2.2 ODN Physical Layer Sub-Layering From a physical layer point of view, both an SDH/SONET frame and an optical transport network (OTN) frame can be adopted, SO as to leverage on the widely diffused circuitry built on these standards. From a layering point of view, even if it uses largely Optical/Electrical/Optical con- version, the ODN lacks the partitioning of the physical layer into two distinct and autonomous sub-layers typical of synchronous digital hierarchy (SDH) over WDM networks. This simplification is useful to maintain a simple control plane and to avoid redundant signaling due to the need of synchronization between the physical sub-layers. Due to the concept of bandwidth virtualization, the ODN would be equipped with a complex and flexible adaptation layer for the interface with the client layers. The adaptation function has the role of receiving a bandwidth allocation request from the suitable upper layer protocol together with the indication of the quality of service (QoS) class required for the physical connection to be set up. Once the request is received, it is matched with a channel at the physical layer equipped with the survivability mechanism most suited to assure the required QoS level among those available at physical layer. Telecommunication Networks If multilayer survivability is possible, it is the adaptation function that receives the coor- dination protocol from the client layer and transforms it into a physical layer protocol to be elaborated by the relevant physical layer entities. When the physical layer network ele- ments produce a feedback to be passed t