Network slicing is an important concept for telecom-munication companies for optimizing their infrastructure and providing customized services. In order to deploy them, it is necessary to fully understand the customer requirements. The Communication Service Management Function (CSMF) is an entity that has this task, acting as a gateway to translate these requirements towards the network slicing ecosystem. Even though we know the tasks for the CSMF, we find there is no complete definition of its internal elements and interactions. Our contribution is threefold: (i) we provide a comparison with current implementations and their weaknesses; (ii) we propose a complete model of the CSMF, its internal structure and its interaction with other elements of the network slicing infrastructure; and (iii) we demonstrate use case examples that show the functionality of the complete model.