Very small aperture terminal
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A VSAT for Very Small Aperture Terminal is a 2-way satellite ground station with a dish antenna that is smaller than 3 meters, as compared to around 10 meters for other types of satellite dishes. VSAT is most commonly used for point of sale transactions including credit cards and RFID applications such as Mobil Speedpass. There are over 100,000 gas stations in the United States alone that use VSAT.
The first commercial VSATs were C band (6 GHz) receive-only systems by Equatorial Communications using spread spectrum technology. More than 30,000 60 cm antenna systems were sold in the early 1980s. Equatorial later developed a C band (4/6 GHz) 2 way system using 1m x 0.5 m antennas and sold about 10,000 units in 1984-85.
Schlumberger Oilfield Research co-developed the world's first Ku band (12/14 GHz)VSATs with Hughes Aerospace in 1985, to provide man-portable network connectivity for oil field drilling and exploration units. VSAT's are still used at well sites today to transmit real-time data back for processing.
VSAT is plus also used by local car dealerships affiliated with manufacturers such as Ford and General Motors, for transmitting and receiving sales figures & orders, as well as for receiving internal communications, parts ordering, service bulletins, and interactive distance learning training courses from the manufacturer. The FordStar network, used by Ford and its local dealers, is an example of this.
Wal-Mart stores across the USA also use store-installed VSAT systems for communications (as a backup, normally leased lines are used) to Wal-Mart's corporate headquarters for sending information on inventory and sales transactions.
VSAT technology is also used for 2-way satellite internet providers such as DirecWay and StarBand in the US, and Amariska, Bluestream & Technologie Satelitarne in Europe, among others. (Direcway is also available in Europe, South America, India and China.) These services are used across the world as a means of delivering broadband internet access to sites which cannot get ADSL or cable internet access, which are usually remote or rural locations.
Nearly all VSAT systems are now based on IP, with a very broad spectrum of applications. At December 2004, the total number of VSAT terminals ordered stood at over 1 million with nearly 650,000 sites in service. Annual VSAT service revenues were $3.88 billion, with TDMA & DAMA hardware revenues at $746.9 million (source: www.comsys.co.uk).''
[edit] Topologies of VSAT
Most VSAT networks are usually configured in one of these topologies:
- A star topology, using a central uplink site, such as a network operations center (NOC), to transport data back and forth to each VSAT terminal via satellite,
- A mesh topology, where each VSAT terminal relays data via satellite to another terminal by acting as a hub, minimizing the need for a centralized uplink site,
- and a combination of both star and mesh topologies. Some VSAT networks are configured by having several centralized uplink sites (and VSAT terminals stemming from it) connected in a multi-star topology with each star (and each terminal in each star) connected to each other in a mesh topology. Others configured in only a single star topology sometimes will have each terminal connected to each other as well, resulting in each terminal acting as a central hub. These configurations are utilized to minimize the overall cost of the network, and to alleviate the amount of data that has to be relayed through a central uplink site (or sites) of a star or multi-star network.
Star topology services like Direcway and others can be used to provide broadband wide area networks, as well as to provide broadband internet access. Applications of this include intranet networking for front and back office applications, managed store and forward solutions such as digital signage, and interactive distance learning.
