rst ODN networks are built with concatenated rings. If from a technological point of view an ODN OADM is quite an innovative machine, from Channel Add/drop switch channels High speed Deserializer signal after regeneration Deserializer Wavelength switch Synchronization Tests and clock generation reallignement Clock period Original and scaled clock scaling distribution FIGURE 10.6 Possible architecture of an ODN OXC. Telecommunication Networks a functional point of view it sums up all the functionalities of a next generation SDH/ SONET ADM and of a tunable OADM. Due to the possibility of managing whole wavelengths at a wavelength layer or single channels at the channel layer, the ODN OADM, can manage two types of rings: wave- length rings (WRings) and channel rings (CRings). As far as WRings are concerned, they are similar to OTN self-healing rings. The elemen- tary unit transmitted and managed at the nodes is a wavelength, even if two elements make ODN WRings superior to OTN Rings. The first property consists in the fact that since wavelengths are regenerated at each node, the logical wavelength path that is set up along the ring does not require physical wavelength continuity: wavelength conversion can be operated even at each node. The fact that the wavelength can change even at every node along the path is really beneficial in the exploitation of the backup capacity if shared protection is used. Moreover, optimum use of all the wavelengths can be done along the ring. The second property is the ability to perform grooming at the channel layer that com- pletely lack to OTN OADM. Considering CRings, these are a structure completely new: under certain points of view they are similar to SDH/SONET path layer rings. Differently from SDH/SONET, however, a single machine, the ODN OADM, manages several superimposed rings together, being able to change the channel routing from one ring to the other in order to better exploit the available transmission capacity. In a CRing, channels can be moved from one wavelength to the 