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Chapter 8 Control and Management > 8.3 Layers within the Optical Layer - Pg. 478

478 Control and Management Electronic layer OTU OCh Optical layer OMS OTS OTS OMS ODU OTU OCh OMS OTS OTS OLT OADM Amplifier Transponders/regenerators Figure 8.2 Layers within OTN. The optical layers are the optical channel layer (OCh), optical multiplex section (OMS) layer, and the optical transmission section (OTS) layer. The electronic layers are the optical channel data unit (ODU) layer and the optical channel transport unit (OTU). layer, and also if there is a need to set up and take down connections rapidly as we discussed above. We will discuss this issue further in Section 8.6. 8.3 Layers within the Optical Layer The optical layer is a complicated entity performing several functions, such as mul- tiplexing wavelengths, switching and routing wavelengths, and monitoring network performance at various levels in the network. In order to help delineate management functions and in order to provide suitable boundaries between different equipment types, it is useful to further subdivide the optical layer into several sublayers. We will use the Optical Transport Network (OTN) architecture introduced in Section 6.2 as a model of a layered optical network, as shown in Figure 8.2. In Section 6.2, we primarily discussed the electronic layer of OTN. Now we turn our attention to the optical layer. At the top is the optical channel (OCh) layer. This layer takes care of end-to- end routing of the lightpaths. We have been using the term lightpath to denote an optical connection. More precisely, a lightpath is an optical channel trail between two nodes that carries an entire wavelength's worth of traffic. A lightpath traverses many links in the network, wherein it is multiplexed with many other wavelengths carrying other lightpaths. It may also get regenerated along the way. Note that we do not include any electronic time division multiplexing functions in the optical layer.