A Communications Viewpoint contains descriptions of the Physical Data Flows that pass between Sub-systems (and Modules) in the Physical Viewpoint. See also “What is a Physical Viewpoint?“.
A Communications Viewpoint will contain statements, or examples, of the data that flows between Sub-systems (and Modules) and from which communications specifications can be written. Some links may require the use of existing communications standards, others may require a new communication standard to be written. In the latter situation the corresponding part of the Communications Viewpoint can used as a starting point.