Inmarsat
|
|
INMARSAT, is an international telecommunications company founded in 1979. It operates a fleet of nine (as of 2003) geosynchronous telecommunications satellites. The organization is mostly owned by national telephone companies.
Inmarsat-3.gif
Satellite_phone.jpg
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 becomes less reliable as you near the north and south poles, depending on the ionosphere , becoming unusable beyond around 75° of latitude.
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 the B-GAN 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 are:
- 871 Atlantic - East
- 872 Pacific
- 873 Indian Ocean
- 874 Atlantic - West
Historically expensive, calls via Inmarsat have now dropped 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 charged for the amount of data they send and 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.
There are several possible standards offered by INMARSAT:
- INMARSAT-A: analogue, for telephone, fax, telex, e-mail and data transfer.
- INMARSAT-B: digital, lower cost.
- INMARSAT-M: digital, portable personal mobile satellite phone, voice transfer with 4,8 kbit/s and data and fax transfers with 2,4 kbit/s
- INMARSAT-MINI-M: digital, using INMARSAT's zonal ray technology
- INMARSAT-M4: voice transfer with 4,8 kbit/s and data with 64 kbit/s, ISDN, IPDS
- INMARSAT-C: low-speed transfer of messages, standard approved for usage in the GMDSS system, equipped with GPS.
See also telephone, Marine and mobile radio telephony