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3-1
3. DSC OVERVIEW
3.1 What is DSC?
DSC is an acronym meaning Digital Selective Calling. It is a digital distress and general
calling system in the MF and HF bands used by ships for transmitting distress alerts and
general calls and by coast stations for transmitting the associated acknowledgements.
For DSC distress and safety calling in the MF and HF bands, the frequencies are 2187.5,
4207.5, 6312.0, 8414.5, 12577.0, and 16804.5 kHz.
The DSC station sends and receives DSC general and distress calls via the radiotelephone.
TRANSCEIVER
UNIT
Distress Frequency
Routine DSC Call
Routine DSC Calls
Option
CONTROL UNIT
3.2 DSC Message
DSC calls are roughly divided in two groups: distress, urgency and safety messages, and
routine messages. Below are the types of DSC messages.
Call Description
Distress Alerts Your ship sends distress message
Distress relay area Your ship relays distress call to all ships in a specific geographical area
Distress relay coast Your ship relays distress call to a coast station
Medical Transport Inform areas that your ship is carrying medical supplies*
Neutral Craft Inform areas that your ship is not a participant in armed conflict*
Individual Call to a specific address
PSTN message Call over Public Switched Telephone Network (PSTN)
Test message Send test signal to a station to test your station’s functionality
Group message Call to a specific group
Area message Call to all ships in a specific geographical area
Position Your ship requests position of other ships
Polling message Confirm if own ship is within communicating range with other ships.
(Receive and answer only)
*Special Message: When sending these messages, set the acknowledgement. See section
6.15.