In the UK, MMSIs are issued by Ofcom when they are requested to do so by ticking a box on the application form or renewal form for a Ship Radio Licence.
The first three digits of a ship’s MMSI are known as the Maritime Identification Digits (MID), and indicate the country which issued it.
All UK vessels have MMSIs which begin with the numbers 232; 233; 234; or 235 e.g. 232089001.
Coast radio stations also have nine-digit MMSIs, but to distinguish them from ships and boats, their MMSIs always begin with two zeros. This is followed by the three-digit MID, then by four more digits:
e.g. Milford Haven Coastguard 002320017.
DSC can also handle group calls, to a group of vessels which share some common interest, such as all vessels belonging to one company, or all the yachts taking part in a race. The Group MMSI is allocated by Ofcom on request, and consists of a single zero, followed by the MID, then by five more digits:
e.g. 023208591.
A DSC controller must have its MMSI stored in its memory before it can be used. Most Class D controllers allow individual owners to do this themselves... but only once. If you make a mistake, or if you move the controller onto a boat with a different MMSI, the controller will have to be returned to its supplier to have its memory erased.
Group MMSIs, however, are different: these can be saved and deleted as often as you like.
Types of call
The DSC code allows calls to be classified into six different types:
Distress,
All ships,
Individual — a call to a specific vessel or coast station;
Geographic area — to all stations within a designated area (not on class D controllers);
Group call — to all stations sharing a “common interest” and with the same Group MMSI;
Automatic or semi-automatic service call through a coast radio station to a public telephone system (not on class D controllers).
These tell the DSC controller at the receiving end what will be in the rest of the DSC message, and how it should react: it may sound an audible alarm for an incoming distress message, for instance, that is quite different from the alarm sound associated with a routine ship-to-ship call.
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