ored") sub-networks rather than just leased lines, and is proving valuable for mobile backhaul. When ASON is applied, "optical switching" replaces the former name "cross-connection" for the action of high capacity circuit switches based on SDH/OTN. This form of "optical switching" is misnamed and done electronically, not to be confused with true optical domain switching, done typically by WSS (wavelength selective switch- ing) mirrors in ROADMs. The combination of ASON, tunable lasers and advanced ROADM switches minimizes site visits and is sometimes called Zero Touch Photonics. 7.4.1.8.2 Advancement in Switching ROADM (Reconfigurable Optical Add-Drop Multiplexer) technology also allows traffic to pass through a network location transparently in the optical domain without OEO (optical-electrical-optical) conver- sions. ROADMs are used in both metro and long-haul systems with DWDM allowing carriers to move beyond static connections between network nodes to an infrastructure capable of adding or dropping any wavelength at any node (Figure 7.14). This ability redirects stranded optical capacity to match evolving bandwidth requirements without network re-engineering. Formerly, the network tuning pro- cess was performed manually and required considerable equipment, traffic management and personnel [19,21]. ROADM becomes more advantageous with WSS devices. WSS is a single input multiple output solution and supports GMPLS control plane. GMPLS offers a common control plane for TDM, packet and optical networks. WSS increases the number of DWDM ports per ROADM and allows connecting multiple rings without OEO conversion. Thus, ROADM enables adaptive optical infrastructure to cater for IPTV and next generation business solutions. 7.4.2 Data Link Layer Technologies Data Link or Layer 2 of the OSI model provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the physical layer. We will briefly discuss some key lay