What are DSC and MMSI? – Complete guide for maritime safety communication

DSC – Digital Selective Calling for VHF radio: How it works, its benefits, and why it is key to increased maritime safety

DSC, or Digital Selective Calling, is an international standard for digital communication via VHF radio (as well as MF and HF). It is primarily used to send distress calls to other vessels and coast stations, but can also handle urgent, safety, and routine calls.

With DSC, you can make or receive calls directly, without listening to a loudspeaker. When a distress call is sent via DSC, important information such as the vessel's identity (MMSI) and, if the radio is connected to GPS, also the current position, is automatically transmitted. This saves vital time and improves rescue efforts.

Benefits of DSC

• Automatic distress calls with identity and position
• Direct contact with the Coast Guard
• 15–25% longer range than voice calls
• Dedicated channel (channel 70) that is automatically monitored

A DSC distress call is received by all nearby vessels and coast stations with DSC equipment. The alarm is repeated until acknowledged to ensure it is not missed.

MMSI (Maritime Mobile Service Identity) – What is it and how do you get your number?

MMSI is a unique 9-digit number that identifies vessels, coast stations, and SAR aircraft – much like a vehicle registration number. MMSI is used in DSC radio and AIS systems to enable direct calls between vessels and shore stations.

Categories of MMSI

• Ship station
• Group ship station
• Coast station
• Group coast station
• SAR aircraft
• Navigational aids and small craft

To obtain an MMSI, a license from the Post- och telestyrelsen (Swedish Post and Telecom Authority) is required. It is illegal to use or install radio on board without a license. Once the license is granted, the MMSI is assigned to the vessel, and all radio equipment must use this number for safety and maritime traffic management.

Why are DSC and MMSI crucial for maritime safety?

DSC and MMSI make it possible to communicate quickly and efficiently in emergency situations, which can save lives. By combining DSC with GPS and correct MMSI registration, you get a modern and safe communication system on board.