GLOBAL MARITIME DISTRESS AND SAFETY SYSTEM (GMDSS) DIGITAL SELECTIVE CALL (1)
GENERAL
The GMDSS enables Maritime Rescue Centres and radio stations to keep automatic watch on the
distress channels. A ship equipped with a DSC apparatus can make a distress call by simply
pressing a button, which results in an automatic alarm signal at the maritime rescue centre nearest
to the vessel.
DSC can be used for all kinds of radio calls between ship-ship and ship-shore–ship. DSC calls are
made on channel 70, which means that any voice communication on this channel is not allowed.
The DSC call includes and shows the following information:
- Format or Type of Call
- Receiver or Party ID
- Call Category or Priority
- Telecommand
(follow-up radio communication)
- Working Channel
1. FORMAT OR TYPE OF CALL
One of the following are chosen on the DSC apparatus:
- distress alert / distress call in a distress
- all ships a call to all stations
- selective/individual a call to one station
(e.g. in routine calls)
- group a group of stations
- area / geographical call to stations in a
particular area

2. PARTY/RECEIVER ID (IDENTIFICATION)
The receiver of the call (Party ID) you can click either the Maritime Mobile Service Identity (MMSI)
number of the recediving station, a group call number or area call number. The MMSI always
contains nine digits.
Example of MMSI Number system:
MMSI Vessel Explanation
230252000 230 country code (Finland)
always three digits
252000 (ship’s number)
MMSI Coast Station Explanation
002301000 00 means coast station in general
230 country code (Finland)
number of particular coast station
1000 (Turku Maritime Rescue Coordination Centre)

3. CALL CATEGORY OR PRIORITY
- distress
- urgency
- safety
Routine Communication can be of two kinds:
- routine
- ship’s business

4. TELECOMMAND
This gives information on what kind of follow-up radio communication the sender wishes to have. It
also gives information on what kind of message the sender is giving. The most common
telecommand choices include:
- telephony G3E/F3E simplex
o voice communication on VHF
- distress acknowledgement
o request for acknowledgement of distress call
- distress relay alert
o request for relay of distress
- ship’s position
o request for a vessel’s position to be shown on DSC (routine call)