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INMARSAT, is an international telecommunications company founded in 1979. It operate a fleet of nine (2003) geosynchronous telecommunications satellites. The organization is mostly owned by national telephone companies.

INMARSAT provides telephony and data services to users world-wide, via special digital radios called "terminals". An INMARSAT terminal contacts the satellite and communicates to a ground station through the satellite. It provides reliable communications services to a range of governments, aid agencies, media outlets and businesses needing to communicate in remote regions or where there is no reliable terrestrial network. Service can be unreliable near the north and south poles, depending on the ionosphere.

Services include traditional voice calls, low-level data tracking systems, and high-speed data services. The most recent of these provides GPRS-type services at up to 144kbit/s via an IP satellite modem the size of a notebook computer. Other services provide mobile ISDN services used by the media for live via videophone reporting on world events.

The telephone country codes for Inmarsat is:

Historically expensive, calls via Inmarsat have now reduced to a level where they are comparable and in many cases favourable, to international roaming costs, or hotel phone calls.

Newer services using IP technology feature an always on capability where the user is simply charge for the amount of data they send an receive rather than the length of time they are online. Call charges are also the same wherever in the world the service is used. Older services used digital speech coding and required a dedicated channel.

The satellites are digital transponders that receive digital signals, reform the pulses, and then retransmit them to ground stations. The ground stations perform billing and act as gateways to the public switched telephone network and internet.

See also telephone, Marine and mobile radio telephony

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