llows the control plane to identify the functionality of an equipment from the labeling of its ports. In particular, the ports of routing equipments are classified in several classes that are as follows: Fiber switching capable ports (FSC): These are the ports of equipment that can switch the entire fiber signal as a whole. Wavelength switching capable ports (WSC): These are ports of equipment that can switch the single wavelength signal as a whole; since generally the port is occu- pied by a WDM system, a demultiplexer is expected SO to divide at least a certain number of wavelengths (see the OADM structure in Chapter 6) SO to be able to deal with each wavelength independently. Time division multiplexing switching capable ports (TSC): These are the ports of equipment that can switch the single TDM frame; since generally the port is occu- pied by a complete TDM frame, a TDM demultiplexer is expected after the TSC. Layer 2 frames switching capable ports (L2SC): These are essentially the ports of Ethernet equipments. Packet switching capable ports (PSC): These are the ports of LSR and IP routers. Every type of port has a different kind of generalized label SO that the control plane can identify the type of port and SO understand the equipment capability. An example of dif- ferent types of ports is reported in Figure 8.9, where a core node hosting the overlay of an OXC and an LSP router is schematically shown. A few of the wavelength GLSPs transit- ing through the OXC are also sent to the LSR both for local dropping and for grooming, while other wavelength GLSP directly transit through the OXC. This is a typical overlay node configuration, where the OXC ports are wavelength capable ports, while the LSR ports are packet capable ports. Finally ports with multiple switching capability can be defined, for example both PSC and WSC. When a GLSP requires the use of the port it also requires the functionality he needs among those available. 8.3.1 GMPLS Data Paths and Generalized Labels Hierarchy A data path between two GLSR