l records of the connections between transponders and add/drop ports needs to be maintained and updated as changes are made. Advances in photonics, most notably the availability of high-density, cost-effective wavelength selective switches, have made it commercially viable to build a layer of photonic switching that allow the output of a transponder to be connected to any outgoing fiber on the ROADM. By doing this, the limitations that exist in today's ROADMs are removed. The industry uses the terms color- less, directionless, and contentionless to describe this new level of flexibility that has been incorpo- rated into ROADMs [6]. Figure 13.7 illustrates how wavelengths can be created and rerouted completely through software control. The green wavelength was initially built. The transponders supporting the green wave- length could later be repurposed to use a different color (purple) and path, without manual dispatch. Alternatively, the green wavelength could be removed and each transponder could be repurposed to create a new wavelength to any other transponder in the optical network. This flexibility can be exploited for many uses: Restoration: Consider a case where a fiber is cut or an OA fails. Today's networks rely purely on robust L3 network designs and over-provisioned capacity to restore around the failure until the cable can be respliced or the failed equipment replaced. This creates a compro- mised position during the failure and exposure to service outages if subsequent failures occur. With a flexible ROADM, the optical wavelengths can be rerouted around the failure point and service quickly restored. The failure can then be repaired on a scheduled basis. Network optimization: Networks grow over time. At one point in time, the best path to route a connection between offices A and Z may be to traverse intermediate offices B and C. If over time, sufficient demand existed directly between A and Z it might be more efficient to build an express fiber between those two offices. With a flexible ROADM, it is n