To enable just-in-time operations, the various actors engaged in sea transport related actions need to contribute to the creation of common situational awareness. PortCDM (Port Collaborative Decision Making), as one of the concepts of Sea Traffic Management (STM), is a key enabler for reaching the full effects of STM as safe, efficient and sustainable transport from berth-to-berth. The purpose of PortCDM is to provide a basis for the collaboration between key actors within the port and towards its surroundings by enabling situational awareness. Such establishment of situational awareness and use of the information from different sources requires a standardized way of capturing the communication within the port and to port-related actors. In this paper the constituents of PortCDM are introduced followed by a proposed way to conceive Port Call Messages with its different facets.