The spectrum sliced Elastic Optical path Network (EON), which is able to allocate appropriate optical spectrum range and modulation format to an optical path according to the client (e.g. IP) traffic demand and path attributes (e.g., physical length or optical impairments), has been proposed to more efficiently utilize network resources. For a dynamic and intelligent end-to-end path provisioning and IP traffic offloading in an EON, a control plane is a key enabling technique. Therefore, a lot of studies have started to design a GMPLS-based control plane for flexible grid DWDM networks. Despite massive progress, it should be noted that such studies mainly focused on the control of the optical layer.