Electric power systems are immersed in a period of change where new agents are appearing (like the Electric Vehicle Service Provider), and new services are needed, with the Smart Grid concept in mind. These new services require advanced communication infrastructure to support information and data flows. Therefore, it is necessary to identify and specify communication interfaces between new and existing entities. This task entails the definition of message types and information exchanged within every Protocol Data Unit. In this paper, the communication interfaces of the Service Provider entity are identified, and a use case for Energy Planning Validation is described.