Huawei Nokia Telefonica Telefonica Infinera China Unicom CTTC NEC There are scenarios, typically in a hierarchical SDN context, in which an orchestrator may not have detailed information to be able to perform an end-to-end path computation and would need to request lower layer/domain controllers to calculate some (partial) feasible paths. Multiple protocol solutions can be used for communication between different controller hierarchical levels. This document assumes that the controllers are communicating using YANG-based Application Programming Interface (APIs). This document describes some use cases for an Application Programming Interface for path computation. A related yang model will be proposed in a next version or in another document.