The emerging Software Defined Networking (SDN) paradigm separates the dataplane from the control plane and centralizes network control in an SDNcontroller. Applications interact with controllers to implement networkservices, such as network transport with Quality of Service (QoS). SDNfacilitates the virtualization of network functions so that multiple virtualnetworks can operate over a given installed physical network infrastructure.Due to the specific characteristics of optical (photonic) communicationcomponents and the high optical transmission capacities, SDN based opticalnetworking poses particular challenges, but holds also great potential. In thisarticle, we comprehensively survey studies that examine the SDN paradigm inoptical networks; in brief, we survey the area of Software Defined OpticalNetworks (SDONs). We mainly organize the SDON studies into studies focused onthe infrastructure layer, the control layer, and the application layer.Moreover, we cover SDON studies focused on network virtualization, as well asSDON studies focused on the orchestration of multilayer and multidomainnetworking. Based on the survey, we identify open challenges for SDONs andoutline future directions.
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