The statutory requirements regarding radio communications at sea are indeed talking about GMDSS requirements as follows.
GMDSS (Global Maritime Distress and Safety System) is required for most vessel types, as specified in the applicable IMO (International Maritime Organization) publications:
Chapter IV in IMO SOLAS requires all cargo ships above 300 gross tons, and all passenger ships, on international voyages to be provided with a GMDSS installation.
Chapter 14 in the IMO HSC Code requires all HSLC to be provided with a GMDSS installation, and
Chapter 11 in the IMO MODU Code requires MOUs to be provided with a GMDSS installation.
Additional regulations required by some flag states.
DNV approves the GMDSS installation based on the requirements as set out in the above mentioned codes and regulations, on behalf of the vessel’s flag administration.