This document defines the principles, methods and requirements for message exchanges between ships, ship representatives, and other shore parties via a peer-to-peer communication system. This document defines the message structure, including how the data content is assembled from other parts of the ISO 28005 series, and how digital signatures for authentication, integrity, and confidentiality of the message can be used. It also specifies a transport protocol, the basic message exchange patterns, and the protocol related roles of each party in the message exchange. Furthermore, it specifies how more specific message implementation guides (MIGs) are provided for each type of communication application.