Modern IP/Optical transport networks are seldom jointly operated and optimized, and do not cater to the usually implicit requirements of applications, which ultimately drive network traffic. In this concept paper we propose a Software Defined Networking (SDN) based Network Orchestrator to manage multi-layer transport networks while taking explicit application requirements into account. We discuss its architecture and requirements, an interface to allow applications to explicitly specify their requirements in a network-agnostic manner, and possible strategies to optimize the network taking these requirements into account.