They are divided into conventional and satellite communications

Conventional (terrestrial) communications:

They operate in the MF, HF, and VHF frequency areas. They use the digital selective-calling (DSC), radiotelephony, radioteletypy, NAVTEX and RADAR transmitters.

Satellite communications:

They are conducted via the satellite systems Inmarsat and Compass-Sarsat.

Inmarsat:

International satellite maritime organization that operates with four geostationary satellites that characterize the four oceanic regions of the system:

AOR- E: Atlantic Ocean Region East

AOR- W: Atlantic Ocean Region East

POR: Pacific Ocean Region

IOR: Indian Ocean Region

Cospas-Sarsat:

A polar- orbiting satellite system that receives and retransmits ‘EPIRB’ distress alerts.