The International Mobile Satellite Organization (Inmarsat), previously the International Maritime Satellite Organization, was established by IMO in 1979 to operate satellite maritime communication systems and has become a privately owned company, while retaining its public sector obligations to the maritime distress and safety system. Inmarsat became operational in 1982.

Inmarsat uses geostationary satellites at four different positions from which it serves four different regions of the world:

The satellites cover the entire globe except for the polar regions (above 75 degrees north and 75 degrees south).

Apart from global beam coverage, newer satellites also have spot beams to create services with a higher data speed.

Inmarsat offers a variety of services:

Inmarsat-A is the old analogue service of Inmarsat that provides analogue telephony services. Inmarsat-A can also provide data services and fax at a speed of 56 or 64 kbit/s. Inmarsat will be phased out by December 2007.

Inmarsat-Aero provides voice, fax and data services for aircrafts. The data speed depends on the type of terminal used.

Inmarsat-B provides voice, data and fax services at a speed of 9.6 kbit/s and a high speed service at 56, 64 or 128 kbit/s. Inmarsat-B uses a rather large dish antenna which has to be kept pointed to the satellite.

Inmarsat-C is a low speed data services which uses a small omni directional antenna. Data speed is around 600 bit/s.

Inmarsat-M provides a low speed voice service (4.8 kbit/s) and data at a speed of 2.4 kbit/s. Not much used (Inmarsat-Mini M is used instead)

Inmarsat-Mini M provides the Inmarsat-M service with a small and compact satellite terminal. However, the antenna has to be pointed towards the satellite.

Inmarsat-M4 / GAN provides Inmrsat-M services plus Mobile ISDN at 64 kbit/s and a shared packet switched service at 64 kbit/s (MPDS: Mobile Packet Data Service). This service is also known as Global Area Network. The M4 service for aircrafts is known as Swift-64.

Inmarsat-Fleet is a family of services, including Inmarsat-Fleet77, Inmarsat-Fleet55 and Inmarsat-Fleet33. Inmarsat-Fleet provides a low speed voice service (4.8 kbit/s) and a fax service at 9.6 kbit/s. On top of that, Inmarsat-Fleet55 provides a 64 kbit/s Mobile ISDN and MPDS service and Inmarsat-Fleet77 provides Mobile ISDN and MPDS at 128 kbit/s. Inmarsat-Fleet77 also provides a maritime distress service for GMDSS.

Inmarsat-D/D+ is Inmarsats paging service. The original Inmarsat-D terminals were one-way (receive only) terminals. The Inmarsat-D+ service provides a return channel. Inmarsat-D+ can be used for GPS tracking.

Inmarsat-BGAN (Broadband Global Area Network) uses the spot beams of the Inmarsat-4 satellites to offer a high speed packet data service with a maximum data speed of 492 kbit/s.

Inmarsat-RBGAN (Regional BGAN) offers a shared-channel packet switched IP service at data speeds up to 144 kbit/s. RBGAN can only be used in certain parts of Europe, Africa, Asia and Australia.

See also