About MMSI Numbers - By Tim Hasson, Marine Computer Systems

The acronym MMSI stands for Maritime Mobile Service Identity. Sometimes called a "DSC Number", an MMSI is a 9-digit code that can be programmed into certain types of radio equipment, such as a marine radio with Digital Selective Calling (DSC). All INMARSAT satellite terminals use an MMSI number as the heart of their identification string, and the numbers are also used by 406Mhz EPIRB's (Emergency Position Indicating Radio Beacons).

When programmed into marine radio equipment, an MMSI provides a unique, internationally standardized number to identify the vessel. This number also provides a uniform way for authorities to get information about a vessel during a distress incident, and can be used by service providers as a common number for call tracking and billing. In fact, the numbering scheme was carefully designed to allow the worldwide public telephone network to communicate with the equipment on-board automatically. Because it makes sending and receiving voice, telex and e-mail messages to ships direct and automatic, it's convenient to think of an MMSI as being like a telephone number for the boat. While this is certainly true, there are a couple of distinctions worth pointing out.

For instance, while it's common in this day and age to add a second or even third phone line at home, MMSI numbers are designed to be unique to the vessel in question. It's important when licensing and programming the equipment aboard that the vessel receives only one identity, with the same number programmed into all devices.

Like a phone number, devices programmed with an MMSI can be used to "direct dial" another boat, provided similar equipment is aboard the other vessel. VHF DSC is a good example of this use. Increasingly, MMSI's are also used for contact with shore-based service providers, to place phone calls, send e-mail, or to send/receive telex (teletype) messages. While this kind of direct, one-on-one communication is extremely convenient and "telephone-like", the MMSI coding scheme actually goes a step further.

When used with DSC, the MMSI system also provides for something called Group Calling. It is possible, for example, for an owner to simultaneously call every ship in the line to deliver an important message. It is also possible to hail every Coast Guard vessel or coast station within radio range at the same time. Going even further, in an emergency a DSC-equipped boat can transmit a special distress signal to every similarly equipped station that is listening, on land or sea, including nearby commercial vessels. This alert message, which can be activated with the push of an idiot-proof button, includes the MMSI number of the vessel in distress along with its position (provided the radio is linked to a GPS receiver), and even the nature of the emergency. The safety advantages of this kind of instant, automatic alerting are obvious.
 
Because MMSI numbers are unique, authorities (the FCC in the U.S.) can use them to positively identify a vessel in distress. The International Telecommunications Union (ITU) in Geneva, Switzerland, and the Local Coast Guard maintain a database of MMSI's that contains details on every vessel, it's owner, and homeport (recreational boats included) which travels internationally. This Maritime mobile Access and Retrieval (MARS) database is accessible by anyone at http://www.itu.int/cgi-bin/htsh/mars/mars_index.sh . For privacy reasons, access to vessel particulars and emergency contact information is restricted to authorized users only.

At this writing the distress-alerting capabilities of VHF DSC are not completely implemented with the Coast Guard, and probably won't be until 2005 or 2006. In the meantime, nearby commercial vessels may monitor a VHF distress call and relay to the Coast Guard. DSC on HF (single side band) frequencies is further along, with most Coast Guard stations now "on line". The good news is that while Canada and the U.S. may be lagging in some respects, this system is in widespread use in Europe and beyond.

In fact, DSC and MMSI numbers are critical pieces of an internationally agreed-upon plan called the Global Maritime Distress and Safety System (GMDSS). GMDSS is a major rethinking of the emergency communications capabilities required of commercial shipping vessels. Worldwide implementation of this master plan began in the 1990's, and is still ongoing (with occasional interesting debate). MMSI numbers are intended to replace the older Selective Calling (SELCAL) numbers used by radio teletype equipment aboard ships. While MMSI's and other GMDSS enhancements were designed with commercial interests in mind, there is no reason recreational boaters should not take advantage of the safety and convenience these improvements make possible.

By international agreement the International Telecommunications Union sets the rules that determine how MMSI's are assigned and used. In Canada, Industry Canada is responsible for actually assigning MMSI's to commercial and recreational vessels. (In the United States, the Federal Communications Commission (FCC). You will find the appropriate form to register in Canada from this website. (Click Here)

An MMSI number can be obtained when the radio or satellite terminal equipment is first licensed. Note that if you have already commissioned an INMARSAT B, C, or M terminal through COMSAT, then an MMSI number has probably been issued to your vessel. As noted above, this same number should be programmed into other equipment aboard, and a new number should not be requested.

Some recommended "Do's and Don'ts" with respect to MMSI numbers and DSC equipment:

The MMSI Numbering System

A basic understanding of the ITU's MMSI numbering system is key to understanding how the system works, and how to go about using your equipment to call another station.

To begin with, the ITU has assigned every country at least one set of 3-digit Maritime Identification Digits, called a MID. The MID is a "Country Code", and at present the Canada has been assigned the digits "316", "317", and "318", the U.S.  the digits "366", "367", "368", and "369".

The first one or two digits of an MMSI are used to specify whether the ID belongs to an individual vessel, an individual coast station, a group of vessels or a group of coast stations as follows:

 

These leading digits are combined with the MID and other unique digits (assigned by the telecommunications authorities in each nation) to form a complete MMSI. For example:

The exact rules for MMSI number assignment get more complicated when fleets are involved and with different types of satellite terminal equipment.

Tim Hasson is the Mid-Atlantic Representative for Marine Computer Systems Inc.  An avid sailor and amateur radio operator, Hasson has over 18 years of experience with personal computers and wireless communications technologies. He can be reached at 610/287-0703 or via e-mail to thasson@marinecomputer.com