Maritime Mobile Service Identity

A Maritime Mobile Service Identity (MMSI)  is 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 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 initial digits of an MMSI tell something about the identity. The meaning of the first digit is:


 * 0              Ship group, coast station, or group of coast stations
 * 1              Not used (the seven digit identity beginning with "1" is used by Inmarsat A)
 * 2-7          MMSI's used by individual ships, beginning with an MID (see below)
 * 8              Assigned for regional Use
 * 9              Assigned for national Use

Maritime identification digits (MID)
An MID consists of 3 digits, always starting with a digit from 2 to 7 (assigned regionally). 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 written in Table 1 ITU Radio Regulations Appendix 43.

Ship Station Identities
The 9-digit code constituting a ship station identity is formed as follows:


 * MIDXXXXXX

where 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 zero:


 * 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, 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 United States 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.

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.

Source

 * Adapted from http://www.navcen.uscg.gov/marcomms/gmdss/mmsi.htm which, in turn, was adapted from Appendix 43 of the International Telecommunications Union Radio Regulations

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