 layer 3 resources, including router ports, transponders, tails, regenerators, amplifiers, WDM reach table, etc. The layer 0 resource monitoring and maintenance could be very complicated and tightly coupled with the specific equipment. In practice, the specific control of layer 0 is performed by a vendor-provided controller, which provides an open interface to interact with the layer 3 or global SDN controller. This design greatly simplifies the design and operation of resource monitoring and maintenance. 16.4 SDN CONTROLLER MEASUREMENT FRAMEWORK There is a continued need to evolve measurement technologies as the network continues to trans- form. Just as with prior measurement implementations, the service provider needs to monitor compliance with service-Level agreements (SLAs), quickly identify network impairments that impact customer service or reduce network capacity, and isolate such impairments for repair. With the transformation, there is the added emphasis on the automation of detection of net- work impairments, requiring the SDN-related measurement solution to scale to enable such automation. The network transformation to incorporate NFV and SDN, coupled with the advances made in measurement technologies, offers us an opportunity to refresh and optimize the current measure- ment framework for use with SDN-controlled network elements, whether virtual or physical. We are now in a position to leverage these transformations to redesign SDN-related measurement solutions, reaping cost, and efficiency benefits. However, as we move forward, we need to be aware that many of the functional principles imple- mented in the past measurement designs still apply, with this transformation offering us the opportu- nity to optimize the measurement tool footprint that implements them. For example, measurements Network Measurements were traditionally organized into the following categories (and they continue to be relevant to an SDN measurement solution design): Service measurements Network measurements Component measurement