Northbound APIs (SDN northbound APIs) are typically RESTful APIs that are used to communicate between the SDN controller and the services and applications running over the network. Such northbound APIs can be used for the orchestration and automation of the network components to align with the needs of different applications via SDN network programmability1. The management solution is an example of an application that can use the northbound APIs to interact with the SDN controller and configure, monitor, and troubleshoot the network devices and services2. Therefore, the main function of northbound APIs in the SDN architecture is to enable communication between the SDN controller and the management solution. References: 1: What are SDN Northbound APIs (and SDN Rest APIs)? - SDxCentral 2: Software-Defined Networking Security and Network Programmability