This paper covers the first steps in creating a Software Defined Open Architecture Modem (SDOAM). Potentially useful operating environments, platforms and approaches are reviewed as well as relevant work on underwater digital communications at CMRE, including JANUS. A high-level architectural structure, based on a generalisation of the classic OSI communications stack, is proposed, identifying the modules that will make up the system and taking care to include all the features that the major stakeholders will want to see while minimising the investment that will need to be made to migrate from existing systems to SDOAMs. A key new element is the provision of policy engines that will negotiate the switching between different modules in the OSI-like layers. We also propose to formalise the cross-layer linking that is typically found in practical implementations by providing a fully-connected cross-layer framework for all processes to access. Finally, future developments and research directions are identified. The exact definitions of the interfaces between these modules remain to be specified, as is the software support environment on which they will operate.
