Every vessel during at sea has to be capable of performing the nine radio-communication functions of the GMDSS, viz:

– Transmission of ship-to-shore distress alerts by at least two separate and independent means, each using a different radio-communication service.

– Reception of shore-to-ship distress alerts.

– Transmission and reception of ship-to-ship distress alerts.

– Transmission and reception of search and rescue co- ordinating communications.

– Transmission and reception of on-scene communications.

– Transmission and reception of signals for locating.

– Transmission and reception of Maritime Safety Information (MSI).

– Transmission and reception of general radio-telecommunications to and from shore-based radio systems or networks.

– Transmission and Reception of bridge-to-bridge communications.