See IMO's LRIT documents (MSC.1-Circ. 1257 and MSC.263(84)) here . Note that the above mentioned documents revokes the former resolutions MSC.210(81) and MSC.254(83).
All SOLAS vessels must be LRIT capable by 31st December 2008
The International Maritime Organization (IMO) has adopted an amendment to Chapter V of the International Convention for the Safety of Life at Sea 1974 (SOLAS), which introduces new mandatory position reporting obligations for SOLAS ships. It is called Long Range Identification and Tracking (LRIT) and requires vessels to automatically transmit identity and position with date/time at 6-hour intervals.
LRIT came into force on January 1st 2008 with compliance required by 31st December 2008. Vessels required to comply are: