In the past distress and safety relied primarily on the ship in distress alerting another ship for assistance. Now, emphasis is placed on the ability of a vessel to alert SAR authorities ashore as well as shipping in the vicinity to ensure a coordinated response. Shore based authorities now have the primary role of coordinating assistance and rescue operations.

In the GMDSS system the initial acknowledgement of a distress alert should be by the shore-based authorities. Subsequent actions and communications should be controlled by the rescue coordination centre.

GMDSS is based upon the concept of using 4 marine communications areas to determine the operational, maintenance and personnel requirements for maritime radio communication. The areas are designated, A1; A2; A3 and A4.

Global Maritime distress and safety system (GMDSS).