How a satellite call gets routed

How a satellite call gets routed

There are two types of satellite systems under development and each have a different approach to routing phone calls. The proposed satellite systems will use either a bent pipe or an intersatellite linked system.



Bent pipe

In a bent pipe system (Globalstar) a call is placed by a satellite user which is then beamed up to the nearest orbiting satellite. The satellite reflects the call to the nearest ground gateway. Once at the gateway, the call is routed through the public telephone network to the intended receiver of the call. The gateway must be in the line of sight of the satellite, so the system operator must have a significant number of ground gateways to provide direct satellite links. For the most part, a bent pipe system is less complex than an intersatellite linked system because the brains of the system (switching) are on the ground and the satellites are just reflectors in the sky. Bent pipe systems are easier to operate because most of the call is transferred over the public telephone network, this also reduces the cost of the system. Many of the technical features will be located at the gateway which will allows most technical problems to be fixed on the ground.




Intersatellite links

In an intersatellite linked system (Iridium) a user’s call is beamed up to the nearest orbiting satellite. When it reaches the satellite, the call enters the onboard satellite switching system and is routed between satellites up in space. The call is then downlinked to another satellite user or the closest local gateway to the end user. Upon
entering the gateway the call is directed to the intended receiver through the public telephone network. The major benefit of the intersatellite linked system is that it minimizes the cost of the ground segment (i.e. - the call is switched in the air therefore you do not need a ground gateway in the line of sight of each satellite) and it also
minimizes the long distance and interconnect fees (much of which is bypassed in the air). The intersatellite linked system operator is able to keep a larger dollar amount of each call as compared to the bent pipe system operator.However, there is added risk and higher costs because each satellite must have on-board switching capabilities.On-board switching also adds to the complexity of the system because repairs must be made to satellites.