The digital era of 5G and the cloud triggers a new cycle of network investments and presents key opportunity for operators to reflect and reassess the present network and determine what improvements or changes are needed for the future. The evolution and interworking of IP routing and optical transport is a critical success factor for many operators because it greatly determines the quality, reliability and cost-efficiency of their network and the services it delivers. This white paper discusses Nokia’s approach for building smart and software defined network (SDN) fabrics that seamlessly blend IP and optical transport technologies to cost-efficiently meet the service delivery objectives for the digital era.