Huawei Technologies Huawei Technologies China Mobile CAICT Nokia Nokia Generalized Multi-Protocol Label Switching (GMPLS) control allows each network element (NE) to perform local resource discovery (e.g., LMP), routing (e.g., OSPF-TE) and signaling (e.g., RSVP-TE) in a distributed manner. On the other hand, with the development of software-defined transport networking technology, a set of NEs can be controlled via centralized controller hierarchies to address the issue from multi- domain, multi-vendor and multi-technology. An example of such centralized architecture is ACTN controller hierarchy [RFC8453]. Instead of competing with each other, both the distributed and the centralized control plane have their own advantage, and should be complementary in the system. This document describes how the GMPLS distributed control plane can interwork with a centralized controller system in a transport network.