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In 1996, the ITU introduced country code +881 for direct international dialing of phones on GMSS providers. (Inmarsat had already been allocated country code +870.) The next digit following the country code is allocated (two at a time) to a particular GMSS carrier: [1] [2]
Country calling codes, country dial-in codes, international subscriber dialing ... Global Mobile Satellite System (GMSS) 881: Globalstar (Mobile Satellite Service)
As in the other such shared country codes, carriers are allocated number space within this code space plus their identification code (two-digit number in 882 code space, three or four digit number in 883 code space). The phone number for a subscriber of such a service starts with +882/+883 followed by the carrier code.
Low Earth orbit systems including some of the defunct ones have been allocated number ranges in the International Telecommunication Union's Global Mobile Satellite System virtual country code +881. Iridium satellite phones are issued with codes +881 6 and +881 7.
Most commercial voice and some data mobile satellite services are provided by systems operating in the L-band by Iridium, Inmarsat, Globalstar and Thuraya.The L-band spectrum allocated for MSS is between 1.5 and 2.5 GHz, with the upper portion often referred to as the S-band.
The first key system developed by Northern Telecom in the early 1980s was the Vantage TDD system. Unlike the success of the SL1 system, the Vantage system did not catch with the business environment and the Meridian Norstar was developed as its replacement. In 1988, Nortel developed the Meridian Norstar system.
Every SIM card contains a secret key, called the Ki, which is used to provide authentication and encryption services. This is useful to prevent theft of service, and also to prevent "over the air" snooping of a user's activity. The network does this by utilising the Authentication Center and is accomplished without transmitting the key directly.
The original COSPAS/SARSAT system used polar orbiting satellites, but in recent years the system has been expanded to also include 4 geostationary satellites and 50 medium orbiting navigation satellites. Newest designs incorporate GPS receivers to transmit highly accurate positions (within about 20 metres) of the distress position.