Wikipedia
Inmarsat-C is a two-way, packet data service operated by the telecommunications company Inmarsat which operates between mobile earth stations (MES) and land earth stations (LES). It became fully operational after a period of pre-operational trials in January 1991. The advantages of Inmarsat-C compared to Inmarsat-A are low cost, smaller and uses a smaller omni-directional antenna. The disavantages is that voice communication is not possible with Inmarsat-C. The service is approved for use under the Global Maritime Distress and Safety System ( GMDSS), meets the requirements for Ship Security Alert Systems (SSAS) defined by the International Maritime Organization (IMO) and is the most widely used service in fishing Vessel Monitoring Systems ( VMS).
The service works with a store-and-forward method which enables interface with data network transfer including; e-mail; SMS; telex; remote monitoring; tracking (position reporting); chart and weather updates; maritime safety information (MSI); maritime security; GMDSS; and SafetyNET and FleetNET services; two-way messaging; data reporting and polling; Safety/Emergency alerting.
The service is operated via an Inmarsat-C Transceiver or a lower-power mini-C Transceiver. Data transfers between MES and LES at a rate of 600 bits/second. The frequencies for transmitting (TX) are 1626.5MHz -1645.5MHz and for receiving (RX) are 1530.0MHz - 1545.0MHz.
The service is available for maritime, land mobile and aeronautical use.
This system was also used to track the BBC's project " The Box". BBC News followed a container around the world for a year to tell stories of globalization and the world economy.