Digital Selective Calling (DSC)

Maritime Mobile Service Identity (MMSI) numbers

• A Maritime Mobile Service Identity (MMSI) number uniquely identifies a vessel and is only issued to vessels fitted with Digital Selective Calling (DSC) and/or (Satellite) Ship Earth Station (SES) equipment. The UK administration does not normally issue MMSI numbers to EPIRBs/PLBs.
• In order to use SES equipment, arrangements must be made with an Inmarsat Point of Service Activation Entity. An MMSI number is required before the equipment can be commissioned.
• If an MMSI has already been issued for use with DSC equipment and subsequently a satellite earth station terminal is installed, if a new MMSI is required, the DSC equipment may need to be re-programmed. MMSIs issued (as described above) are free of charge as part of a Ship Radio Licence.
• Ofcom notifies the ITU of all vessel MMSI numbers issued by the UK, however it does not notify Portable MMSI numbers. MMSIs are also made available to HM Coastguard to assist in Search and Rescue operations.
• With the advent of VHF/DSC portable radios in  Ofcom has set aside a unique block of MMSI numbers which will be allocated only to this equipment. This enables HM Coastguard to differentiate between alerts sent from fixed and portable VHF/DSC radio equipment. However, such equipment is no longer being produced in the UK and consequently Ofcom only envisages licensing equipment that is only currently on the market.
• Portable VHF/DSC radios must on no account be programmed with the vessel MMSI numbers. HM Coastguard needs to be able to differentiate between the types of equipment sending a DSC alert, as it is possible for the DSC alert from a transportable radio to come from any vessel. The resulting search on the database for vessel details may provide incorrect information that could jeopardise a Search and Rescue operation. The first four digits of a ‘portable’ MMSI will generally be . 

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