What are the communication requirements for GMDSS?

The GMDSS is an internationally recognized distress and radio communication safety system that has been in place for several decades.  The GMDSS is an automated ship-to-shore and ship-to-ship system using satellites and/or terrestrial radio systems with digital selective calling technology.  These systems provide safety-of-life information and communication systems that inform vessels of navigation hazards and weather conditions, and enable distress calls with pertinent location and identification information with the push of a button.  The GMDSS is mandated for ships internationally by the International Maritime Organization (IMO) Safety of Life at Sea Convention (SOLAS), 1974, as amended in 1988, and carries the force of an international treaty.  The procedures governing use are contained in the International Telecommunication Union recommendations and in the International Radio Regulations, and also carry the force of an International Treaty.

Is there any equipment that is common to all GMDSS ships?

Generally, all GMDSS ships must carry a 406 MHz EPIRB, a VHF radio capable of transmitting and receiving DSC and radiotelephony, a NAVTEX receiver, a SART, backup power systems to enable emergency communications if primary power fails and two-way VHF portable radios.