MSI is a broadcast of essential safety-related information such as navigational warnings, meteorological warnings and forecasts to ships. The shore authorities co-operate to structure this broadcast in such a way that receiving equipment can discriminate between information that is relevant to a particular ship and other information that is not relevant.
There are two systems a ship can use to receive MSI: NAVTEX and Enhanced Group Call (EGC):
• NAVTEX is a terrestrial MF system, used to make broadcasts up to around 450 miles from the transmitter. Broadcasts are co-ordinated in time, coverage and content so that ships can limit what they receive to only the specific information relevant to the waters in which they are operating. NAVTEX transmissions are provided for most of the highly populated coastal waters of the globe;
• EGC is used for the broadcast MSI via satellite to Sea Area A3.