A Maritime Mobile Service Identity (MMSI) is effectively a maritime object's international maritime telephone number, a temporarily assigned UID, issued by that object's current flag state (unlike an IMO, which is a global forever UID). An MMSI comprises a series of nine digits, consisting of three Maritime Identification Digits (country-codes), concatenated with a specific identifier. Whenever an object is re-flagged, a new MMSI must be assigned. A 'maritime object' could be anything which requests an MMSI identifier. e.g. a vessel, fixed offshore installation, mobile unit, maritime aircraft, coast station, etc. Communications may be routed to 'individual objects', or to 'groups of objects'. A group call to objects can be based on an object's - locale, owner/operator/fleet, type, etc. or combinations thereof. MMSI 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 any of these objects automatically. Communications are sent in digital form over a radio frequency channel. Types There are now six kinds of maritime mobile service identities: Ship station identities Group ship station identities Coast station identities Group coast station identities SAR aircraft Navigational aids and craft associated with a parent ship Maritime identification digits (MID) An MID consists of three digits, always starting with a number from 2 to 7 (assigned regionally). A second MID can be assigned once the first or subsequently allocated MID 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 can be found in Table 1 of ITU Radio Regulations Appendix 43. The first digit of an MMSI The initial digits of an MMSI categorize the identity, as defined in by Recommendation M.585. The meaning of the first digit is: 0 Ship group, coast station, or group of coast stations 1 For use by SAR aircraft (111MIDaxx) 2-7 MMSI's used by individual ships, beginning with an MID: 2 Europe (e.g., Italy has MID 247; Denmark has MIDs 219 and 220) 3 North and Central America and Caribbean (e.g., Canada, 316; Greenland, 331; Panama, 351 through 357, plus 370 through 373; United States, 303(Alaska), 338(domestic), plus 366 through 369) 4 Asia (not the southeast) (e.g., PRC, 412, 413, and 414; Maldives, 455; Japan, 431) 5 Oceania (Australia, 503; New Zealand, 512), and Southeast Asia (Philippines, 548; Indonesia, 525) 6 Africa