By now, most owners of DSC-enabled VHF radios are familiar with the benefits DSC offers, particularly in emergencies. But your DSC radio can do a bunch of other stuff, too, and the sense I get is that most of us don’t use any of these features! With that in mind, I decided to figure out how Group Calling works.
Perhaps you already knew that you could hail a specific vessel if you know her MMSI number. Well, you can hail a whole fleet too…without needing to know the specific names or MMSI numbers of any of the boats. All you need to know is the Group MMSI number that flotilla uses, and each vessel within range will hear your hail. Participating vessels need to have this Group MMSI number programmed into their radios, of course.
So each fleet, club, or flotilla needs to obtain an appropriate Group MMSI number. To receive a unique MMSI number for your vessel, you go to BoatUS and register online, assuming yours is a recreational craft. It’s free. It’s easy. It might help the Coast Guard find you in the event of an emergency. If you want to learn a lot about MMSI numbers in a hurry, check out this page at Marine Computer Systems.
Guess what, though: It’s not at all clear how one obtains a Group MMSI number! One page on the Coast Guard’s Navigation Center website says this:
Your individual MMSI assigned by the FCC should end in a zero. To obtain a vessel group identity, take any one of your individual MMSI numbers, remove the zero at the end of the number, and add a zero at the beginning. That new number will be your vessel group identity. For example, if your individual identity is 366123450, your vessel group identity is 036612345. If your individual identity does not end in a zero, you will need to obtain a group identity from the FCC or the agency which assigned you your individual identity.
That seems pretty clear. Except that my BoatUS-assigned individual MMSI doesn’t end with zero! And BoatUS doesn’t assign Group MMSIs. And the FCC doesn’t appear to have any facility for allowing me to create a Group MMSI, at least not unless I apply for a Station License ($205 fee) that I don’t need. Hmmm.
Seriously, though, this can’t be right. Take the zero off the end and insert it at the beginning? What?! Really? No way!
As near as I can tell, and as bizarrely improbable as it sounds, it appears that nobody is actually keeping track of Group MMSIs in any coherent way. If this is correct, then you could use anything you like as a Group MMSI, as long as it begins with a single zero. If you wanted it to follow the format even more closely, you could add the three digits corresponding to your country code. For US boaters, that means your fabricated Group MMSI number would begin with 0366 and five more digits. You could run into confusion if you used the same number as some other fleet operating in your area, but how likely is that, really?
Note: I’m NOT encouraging you to make up random MMSI numbers and program them into your radio!
All I want to do is get to the bottom of this mystery. Somebody, set me straight, please! 
Actually, the apparent anarchy I’ve encountered with Group MMSIs isn’t all that far-fetched when you consider the current confusion about individual MMSIs discussed here last week.
6 responses so far ↓
John // Nov 7, 2007 at 9:42 pm
Great use for a great feature. DSC combined with AIS is another powerful feature that I use daily!
Tim Flanagan, Managing Editor // Nov 8, 2007 at 7:15 am
John, this is actually something I want to learn more about. Will DSC-equipped VHF radios send lat/lon and MMSI data received from other vessels over the NMEA network to a chartplotter? If so, will a chartplotter display the location of the other vessels?
In other words, can DSC produce static, only-when-requested position snapshots that could appear on a chartplotter? Sort of a poor-man’s AIS?
Mickey Baker // Mar 23, 2008 at 2:27 pm
Tim,
From the rules as written, I infer that the government doesn’t want to be involved in group mmsi assignments.
Basically, it appears they want you to make up group MMSI’s from individual MMSI’s.
Here’s as complete an explanation as you’ll find anywhere.
Quoting from
http://www.navcen.uscg.gov/marcomms/gmdss/mmsi.htm which looks to be a dead link as I write this - I posted it here from Google Cache, for that reason:
“Your individual MMSI assigned by the FCC should end in a zero. To obtain a vessel group identity, take any one of your individual MMSI numbers, remove the zero at the end of the number, and add a zero at the beginning. That new number will be your vessel group identity. For example, if your individual identity is 366123450, your vessel group identity is 036612345. If your individual identity does not end in a zero, you will need to obtain a group identity from the FCC or the agency which assigned you your individual identity. See the MMSI Webpage.”
And here is a complete explanation of what the individual fields in the MMSI numbers should be:
Maritime Mobile Service Identities
Please see guidance to administrations for the assignment and conservation of maritime mobile service identities (MMSI).
(Adapted from Appendix 43 of the International Telecommunications Union Radio Regulations)
Maritime Mobile Service Identities are formed of a series of nine digits which are transmitted over the radio path in order to uniquely identify ship stations, ship earth stations, coast stations, coast earth stations, and group calls. These identities are formed in such a way that the identity or part thereof can be used by telephone and telex subscribers connected to the general telecommunications network principally to call ships automatically.
There are four kinds of maritime mobile service identities:
Ship station identities,
Group ship station identities,
Coast station identities,
Group coast station identities.
The First Digit of an MMSI
The first digit or two of an MMSI means something, and from it you can tell something about the identity:
First digit(s) Meaning
0X Ship Group identity Coast station, or Group of Coast Stations
1 Not used (the seven digit identity beginning with “1″
is used by Inmarsat A)
2 These are valid MMSI’s used by individual ships
. ”
. ”
7 ”
8 Assigned for Regional Use
9 Assigned for National Use
Maritime Identification Digits (MID)
A single MID has been allocated to each country. A second MID can be assigned once the MID first or subsequently allocated is more than 80% exhausted and the rate of assignments is such that 90% exhaustion is foreseen. A listing of MIDs assigned to each country is provided in table 1 to Appendix 43 of the ITU Radio Regulations.
A MID always starts with a digit from 2 to 7.
Ship Station Identities
The 9-digit code constituting a ship station identity is formed as follows:
MIDXXXXXX
wherein MID represent the Maritime Identification Digits and X is any figure from 0 to 9.
If the ship is fitted with an Inmarsat B, C or M ship earth station, or it is expected to be so equipped in the foreseeable future, then the identity should have three trailing zeros:
MIDXXX000
If the ship is fitted with an Inmarsat C ship earth station, or it is expected to be so equipped in the foreseeable future, then the identity could have one trailing zeros:
MIDXXXXX0
If the ship is fitted with an Inmarsat A ship earth station, or has satellite equipment other than Inmarsat, then the identity needs no trailing zero.
Group Ship Station Call Identities
Group ship station call identities for calling simultaneously more than one ship are formed as follows:
0MIDXXXXX
where the first figure is zero and X is any figure from 0 to 9. The particular MID represents only the country assigning the group ship station call identity and so does not prevent group calls to fleets containing more than one ship nationality.
Coast Station Identities
Coast station identities are formed as follows:
00MIDXXXX
where the first two figures are zeros and X is any figure from 0 to 9. The MID reflects the country in which the coast station or coast earth station is located.
Group Coast Station Call Identities
Group coast station call identities for calling simultaneously more than one coast station are formed as a subset of coast station identities, as follows:
00MIDXXXX
where the first two figures are zeros and X is any figure from 0 to 9.
In the United States
In the U.S., federal MMSIs are assigned by the National Telecommunications and Information Administration, and are normally, but not always, formed as 3669XXXXX. Non federal MMSIs are assigned by the Federal Communications Commission normally as part of the ship station license application (Form 506), and are formed as 366XXX000 for ships on international voyages and ships needing an Inmarsat mobile earth station, or 366XXXXX0 for all other ships.
The U.S. Coast Guard group ship station call identity is 036699999, and group coast station call identity is 003669999.
In the U.S., MMSIs are primarily used for digital selective calling and for assigning Inmarsat identities. For more information, see Maritime Distress & Safety Telecommunication Data Elements
Assignment of Ship Station Identification
(adapted from ITU-R Recommendation M.585-2)
Restrictions may apply with respect to the maximum number of digits which can be transmitted on some national telex and/or telephone networks for the purpose of ship station identification. At present, the maximum number of digits that are transmitted that are able to be transmitted over the national networks of many countries for the purpose of determining ship station identity is six. The digits carried on the network to represent the ship station identity is referred to as the “ship station number” in this text and in the relevant ITU-T Recommendation. The use of the techniques described below should make it possible for the coast stations of such countries to engage in the automatic connection of calls to ship stations.
To obtain the required nine-digit ship station identity a series of trailing zeros is added to the ship station number by the coast station for shore-originated automatic services, e.g.:
Ship station number Ship station identity
MIDXXX MIDXXX000
As long as the restrictions above apply in one’s own network limiting ship station numbers to 6 digits, ships that intend to receive automatic network traffic from national coast stations only, should be assigned identities wherein X(9), but not X(8), =0. This assumes that “9″ is used to abbreviate the national MID for such ships for network purposes.
Ship station number Ship station identity
9XXXXX MIDXXXXX0
As long as the restrictions above apply it may be useful for some administrations to expand the capacity for numerical ship station identification by using as many as ten”8Y” abbreviations for MIDs. Such a technique may allow the assignment of ship station identities wherein trailing zeros are applied only to X(8) and X(9).
Ship station number Ship station identity
8YXXXX MIDXXXX00
The usefulness of this technique to a given administration may depend on whether its abbreviation (e.g. 83) of its own MID is duplicated in other administrations in which some of its ships have a community of interest. When such is the case the ship in question can be called using the same ship station number in all the automatic networks of interest to that ship. As an example, a group of up to ten countries, with community of interest, might agree to assign the same abbreviation for their respective MIDs. The abbreviation should always relate to the numerically lowest MID, when more than one is assigned to a given country.
Country “8Y” Assignment
A 80
B 81
C 82
D 83
E 84
F 85
G 86
H 87
I 88
J 89
All countries recognize a particular 8Y abbreviation as associated with a particular country. For example a coast station in any of the countries A-J receiving “83″as the first two digits of a ship station number would transmit the MID of the country D.
As long as the restrictions described above apply, ships that reply regular automatic communications from foreign coast stations additional to those that may conform to the abbreviation arrangements above shall only be assigned ship station identities with X(7)X(8)X(9) = 000 to support 6 digit ship station numbers.
When it becomes necessary to progress to stage 2, (seven digit ship station numbers for automatic shore-originated traffic) in the ship station identity scheme the format of ship station identities described in the previous paragraph would change from MIDXXX000 to MIDXXXX00. If “8Y” abbreviations are used in stage 1 (six digit ship station numbers for automatic shore-originated traffic) some ship station identity assignments will already have taken the MIDXXXX00 format. It would therefore be useful to reserve at least one value in the X(7) digit position if ship station identity assignments are made on the basis of “8Y” network abbreviations:
Ship station number Ship station identity
8YXXXX MIDXXXX00
Assignment of Identification to Aircraft
When an aircraft is required to use maritime mobile service identities for the purposes of conducting search and rescue communications with stations in the maritime mobile service, the responsible administration should assign a nine-digit unique aircraft identity, in the format 111213M4I5D6X7X8X9 where the digits 4, 5 and 6 represent the MID and X is any figure from 0 to 9. The MID represents only the territory or geographical area of the administration assigning the aircraft call identity.
The administration may use the seventh digit to differentiate between certain specific uses of this class of MMSI, as shown in the example applications below:
a) 111MID1XX Fixed-wing aircraft
b) 111MID5XX Helicopters
The combination 111213M4I5D6070809 should be reserved for a Group Aircraft Identity and should address all 111MIDXXX stations within the administration. The administration may further augment this with additional Group Call identities, i.e. 111MID111, etc.
Assignment of Identification to AIS Aids to Navigation (AtoN)
When a means of automatic identification is required for a station aiding navigation at sea, the responsible administration should assign a nine-digit unique number in the format 9192M3I4D5X6X7X8X9 where the digits 3, 4 and 5 represent the MID and X is any figure from 0 to 9. The MID represents only the territory or geographical area of the administration assigning the call identity for the navigational aid.
The format shown above applies to unmanned AIS AtoN floating in the water and virtual AIS AtoN belonging to aids to navigation systems; however, aids to navigation systems mounted ashore on fixed land or on an island should be assigned an identification number in the format given in Annex 2.
The administration may use the sixth digit to differentiate between certain specific uses of the MMSI, as shown in the example applications below:
a) 99MID1XXX Physical AIS AtoN
b) 99MID6XXX Virtual AIS AtoN
Assignment of Identification to Craft Associated with a Parent Ship
Devices used on craft associated with a parent ship, need unique identification. These devices which participate in the maritime mobile service should be assigned a nine-digit unique number in the format 9182M3I4D5X6X7X8X9 where the digits 3, 4 and 5 represent the MID and X is any figure from 0 to 9. The MID represents only the territory or geographical area of the administration assigning the call identity for the craft associated with a parent ship.
This numbering format is only valid for devices on board crafts associated with a parent ship. A craft may carry multiple devices for which a MMSI is required. These devices may be located in lifeboats, life-rafts, MOB-boats or other craft belonging to a parent ship.
A unique MMSI should be assigned for each device onboard a craft associated with a parent ship and will have to be separately registered and linked to the MMSI of the parent ship.
The Exhaustion of MMSIs
Because all ships on international voyages, as well as all ships fitted with an Inmarsat B or M ship earth station, are assigned MMSIs of the format MIDXXX000, a serious problem has arisen internationally in assigning sufficient numbers of MIDs to all administrations that need them. For example, a country having 10,000 Inmarsat-equipped ships would require 10 MIDs just to accommodate those 10,000 ships. If 50,000 boaters decided to fit small Inmarsat M terminals, 50 additional MIDs would be required to accommodate them.
The problem exists with Inmarsat-equipped ships because ITU-T recommendations require that Inmarsat ship earth stations be assigned the identity (MESIN) TMIDXXXYY, where T indicates the type of Inmarsat station, YY indicates the Inmarsat station extension (e.g.”00″ might indicate a telephone in the bridge, “01″ might indicate a fax machine in the radio room, etc), and MIDXXX indicates the ship station number, which relates to the assigned ship station identity MIDXXX000.
The MMSI was meant to be an all-inclusive ship electronic identity, used in one form or another by every GMDSS or telecommunications instrument on the ship. Questions have been raised, however, whether the MMSI can in practice totally fulfill that role. ITU may eventually end the practice of relating Inmarsat MESIN identities with the ship MMSI identity.
The World radio Conference, Geneva, 1997 (WRC-97), adopted Resolution 344 concerning the exhaustion of the maritime mobile service identity resource. In view of improvements to public switched telephone networks, and new capabilities of the Inmarsat system other than Inmarsat B or M, previous restrictions should no longer be applicable. All nine digits of the MMSI can be used in such cases, and no longer need to end in trailing zeros.
How To Obtain an MMSI Assignment
U.S. Non-Federal User
Commercial users, or those who travel outside the U.S. or Canada, must apply for a ship station license, or an amendment to a ship station license, to obtain an MMSI.
Non-commercial users (e.g. recreational boaters) who stay in U.S. waters can obtain an MMSI through BOAT US and SeaTow.
U.S. Federal User
Federal users can obtain MMSI assignments from their agency radio spectrum management office. These procedures are currently under review by NTIA.
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.
International Telecomms Union Maritime Mobile Access Retrieval System
You can access the list of Maritime Identification Digits assigned to each country, or look up information concerning a vessel using its MMSI or radio call sign from the Telecommunications Union Maritime Mobile Access Retrieval System.
For More Information…
The following are ITU publications dealing with forming and assigning of MMSIs and the usage of MIDs:
Forming and assigning of MMSIs:
Rec ITU-R M.585-2 (Assignment and Use of MMSIs) 1994
Rec ITU-T E.210/F.120 (Ship Station Identification of VHF/UHF and Maritime Mobile-Satellite Services) 1988
Usage of MIDs and MMSIs
Rec ITU-R M.491-1 (Translation between an Identity Number and Identities for Direct Printing Telegraphy in the Maritime Mobile Service) 1994
Rec ITU-R M.493-8 (Digital Selective Calling) 1997
Rec ITU-R M.541-7 (Digital Selective Calling Operational Procedures) 1997
Rec ITU-R M.586-1 (Automated VHF/UHF Maritime Mobile Telephone System) 1994
Rec ITU-R M.587-1 (Coast Station Identities and Initiation of Location Registration in an Automated VHF/UHF Maritime Mobile Telephone System) 1994
Rec ITU-R M.625-3 (Direct-Printing Telegraph Equipment Employing Automatic identification in the Maritime Mobile Service) 1995
Rec ITU-R M.632-3 (Inmarsat E Satellite EPIRBs) 1997
Rec ITU-R M.633-1 (COSPAS-SARSAT 406 MHz Satellite EPIRBs) 1994
Rec ITU-R M.693 (DSC VHF EPIRB) 1994
Rec ITU-R M.820 (Use of 9-digit Identities for Narrow-band Direct Printing) 1994
Rec ITU-R M.825-2 (DSC Transponders) 1997
Rec ITU-T E.211 (Selection Procedures for VHF/UHF Maritime Mobile Services) 1988
ITU-T E.215 (Telephone/ISDN Numbering Plan for the Maritime Mobile Satellite Services of Inmarsat) 05/97 Doc COM 2-R60)
ITU-T F.125 (Numbering Plan for Access to the Mobile-Satellite Services of Inmarsat from the International telex Service) 08/93
All MMSI Were The Borogoves… | Navagear.com // Apr 22, 2008 at 11:03 am
[...] written lots (here and here, particularly) about MMSI—the Marine Mobile Service Identity numbers programmed into [...]
Brian // May 21, 2008 at 8:52 am
Can anyone explain all that to me in ENGLISH? I mean for cryin’ out loud! How is the “Regular Joe”; who doesn’t have a degree in Computer Science or Electronics supposed to use or find or add a DSC number or fleet number to his VHF/DSC radio?
Tim Flanagan, Managing Editor // May 21, 2008 at 11:30 am
Brian, I feel your pain. You have to really WANT to fiddle around with this stuff to get the most out of it, and that certainly wasn’t the intention of the people who dreamed it all up!
If you do nothing else, you should (1) obtain a MMSI number for your boat (which you can do at BoatUS) and (2) program it into your DSC VHF radio (consult your manual). Then make sure your VHF is receiving GPS data.
Once you’ve accomplished all that, THEN start thinking about these “advanced” propeller-head DSC features!
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