Maritime Mobile Service Identities (MMSIs) are nine-digit numbers used by maritime digital selective calling (DSC), automatic identification systems (AIS), and certain other equipment to uniquely identify a ship or a coast radio station. MMSIs are regulated and managed internationally by the International Telecommunications Union in Geneva, Switzerland, just as radio call signs are regulated. The MMSI format and use is documented in Article 19 of the ITU Radio Regulations and ITU-R Recommendation M.585-6, available from the ITU.
How to Obtain an MMSI Assignment
In the United States, the National Telecommunications Administration (NTIA) provides MMSIs to federal users, and the Federal Communication Commission (FCC) provides MMSIs to everyone else. NTIA is as Executive Branch agency under the Department of Commerce, and the FCC is an independent agency.
U.S. Non-Federal User
In order to obtain an MMSI, mariners required by regulation to carry a marine radio and those who travel outside the U.S. or Canada to foreign ports must apply to the Federal Communications Commission for a ship station license or an amendment to a ship station license. State and local governments can generally obtain an FCC ship station license at no charge.
Mariners not required to carry a marine radio (e.g. recreational boaters) and who remain in U.S. waters can obtain an MMSI through approved organizations such as BOAT US 1-800-563-1536, U.S. Power Squadron, and Shine Micro (primarily for AIS).
U.S. Federal User
Federal users can obtain MMSI assignments from their agency radio spectrum management office in accordance with Section 6.6 of the NTIA Manual. Official DHS and U.S. Coast Guard users can obtain an MMSI through Commandant (CG-672) in accordance with Commandant Instruction M2000.3 series, U.S. Coast Guard Auxiliary surface vessel operators should request assignment of MMSIs using the same method as a U.S. Non-Federal user.
Obtaining MMSIs for DSC-equipped VHF Handhelds
A handheld VHF transceiver with DSC and an integral global navigation satellite system (e.g. GPS) not intended for dedicated use on a particular ship (e.g. a diver’s radio) should be assigned a unique 9-digit number in the format 81M2I3D4X5X6X7X8X9. While currently, means do not exist within the U.S. to assign such identities, the Coast Guard has been in discussions with the Federal communications Commission and others on implementing them.
In the interim, VHF handhelds used in the United States should use the MMSI assigned to the ship to which the handheld is primarily associated, even if another radio on that ship uses the same MMSI. Non-commercial users of VHF handhelds not primarily associated with any single ship may use an MMSI provided by an organization such as BOAT US and U.S. Power Squadron (see above). VHF handhelds should not be used ashore absent FCC or NTIA authorization allowing such use.
Outside the U.S.
Outside the U.S., users can obtain an MMSI assignment from their telecommunications authority or ship registry, often by obtaining or amending their ship station license. Canadians can obtain an MMSI from Industry Canada.
How to Update or Change an MMSI Registration
If your MMSI registration information or contact information changes for any reason, you must update your registration. If you sell your DSC-equipped radio or AIS or the boat these devices are mounted on, you must cancel your MMSI registration and should inform the new owner of the need to reregister the MMSI. This is necessary to ensure that the Coast Guard is able to contact the right persons if a distress situation were ever to occur. These registration changes can be accomplished by contacting the organization or agency which originally registered your MMSI. If you do not know which organization registered your MMSI, you can identify that organization by comparing your existing MMSI against those listed in the document MMSI ship station blocks allocated in the US (updated 21 June 2022).
Maritime Identification Digits (MID)
MIDs are three digit identifiers ranging from 201 to 775 denoting the administration (country) or geographical area of the administration responsible for the ship station so identified. See the ITU Table of Maritime Identification Digits.
All ship MMSIs use the format M1 I2D3X4X5X6X7X8X9 where in the first three digits represent the Maritime Identification Digits (MID) and X is any figure from 0 to 9. (Hint: Ships transmitting with an MMSI not starting with the digits 201-775 are likely doing so improperly, and may be subject to FCC or USCG enforcement action).
Groups of Ships (DSC only)
Group ship station call identities for calling simultaneously more than one ship use the format 01M2I3D4X5X6X7X8X9, where the first figure is zero and X is any figure from 0 to 9. The MID represents only the territory or geographical area of the administration assigning the group ship station call identity and does not prevent group calls to fleets containing more than one ship nationality.
No process currently exists to assign non-federal group ship station identities. However, users having an MMSI assigned by FCC license, all of which have a trailing zero, may create a group identity by inserting a zero before the identity and removing the trailing zero (e.g. a user having an MMSI of 366123450 is allowed to use the group identity 036612345).
The U.S. Coast Guard group ship station call identity is 036699999.
Coast Radio Stations (Base Stations)
All coast or base stations use the format 0102M3I4D5X6X7X8X9,where the digits 3, 4 and 5 represent the MID and X is any figure from 0 to 9. Groups of DSC coast radio stations use the same format.
The combination 0102M3I4D506070809 is used to address all 00MIDXXXX DSC stations within the administration. The combination 010293949506070809 is used to address all VHF DSC 00MIDXXXX stations worldwide. These two special combinations are not used in the United States.
The U.S. Coast Guard DSC group coast station identity is 003669999.
Search and Rescue Aircraft
AIS and DSC equipment used on search and rescue aircraft use the format 111213M4I5D6X7X8X9 where the digits 4, 5 and 6 represent the MID and X is any figure from 0 to 9. In the United States, these MMSIs are currently only used by the U.S. Coast Guard.
AIS Aids to Navigation (AtoN)
AIS used as an aid to navigation uses the format 9192M3I4D5X6X7X8X9 where the digits 3, 4 and 5 represent the MID and X is any figure from 0 to 9. In the United States, these MMSIs are reserved for the federal government.
Craft Associated with a Parent Ship
Stations used on craft associated with a parent ship, such as a launches, tenders, towed vessels, etc. may use the format 9182M3I4D5X6X7X8X9 where the digits 3, 4 and 5 represent the MID and X is any figure from 0 to 9. However, no provision currently exists for assigning these identities in the United States. Thus U.S. craft associated with a parent ship must obtain and use a ships MMSI specifically assigned by the FCC or one of their agents. AIS stations used on such vessels, in lieu of an official call-sign should enter “A” followed by the last 6 digits of the MMSI of the parent vessel onto their AIS Call Sign parameter.
AIS Search and Rescue Transmitter (SART)
AIS search and rescue transmitters (SART) use the format 917203X4X5Y6Y7Y8Y9, where the digits 4 and 5 are assigned by the International Association for Marine Electronics Companies (CIRM) and refer to the SART manufacturer, and digits 6, 7, 8 and 9 are sequential digits assigned by the manufacturer identifying the SART.
MOB (Man overboard) (RTCM SC119)
The MOB (Man overboard) device that transmits DSC and/or AIS should use an identity
917223X4X5Y6Y7Y8Y9, (where xx = manufacturer ID 01 to 99 assigned by CIRM; yyyy = the sequence number 0000 to 9999. When reaching 9999 the manufacturer should restart the sequence numbering at 0000.The manufacturer ID xx = 00 is reserved for test purposes). Combination DSC AIS devices will transmit one common user ID.
EPIRB-AIS (RTCM SC110)
The EPIRB-AIS should use an identity 917243X4X5Y6Y7Y8Y9, (where xx = manufacturer ID 01 to 99; yyyy = the sequence number 0000 to 9999. When reaching 9999 the manufacturer should restart the sequence numbering at 0000.).
The user identity of the EPIRB-AIS indicates the identity of the homing device of the EPIRB-AIS, and not the MMSI of the ship.
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