Very small aperture terminal

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A 2.5m parabolic dish antenna for bidirectional Satellite Internet Access.

A Very Small Aperture Terminal (VSAT), is a 2-way satellite ground station with a dish antenna that is smaller than 3 meters. VSATs are most commonly used to transmit credit card or RFID data for point of sale transactions, and for the provision of Satellite Internet access to remote locations.

[edit] Usage

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.

In 1985, Schlumberger Oilfield Research co-developed the world's first Ku band (12 to 14 GHz) VSATs with Hughes Aerospace, to provide portable network connectivity for oil field drilling and exploration units. VSATs are still used at many sites today to transmit data in real time for processing.

VSATs are used by car dealerships affiliated with manufacturers such as Ford and General Motors for transmitting and receiving sales figures and orders, as well as for receiving internal communications, service bulletins, and interactive distance learning courses from manufacturers. The FordStar network, used by Ford and its local dealers, is an example of this.

Walgreens Pharmacy is the largest private user of VSAT, first is the military.

Wal-Mart stores across the US use 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 HughesNet and StarBand in the US, and Bluestream and Technologie Satelitarne in Europe, among others. 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; usually remote or rural locations.

Nearly all VSAT systems are now based on IP, with a very broad spectrum of applications. As of December 2004, the total number of VSATs ordered stood at over 1 million, with nearly 650,000 in service. Annual VSAT service revenues were $3.88 billion (source: www.comsys.co.uk).

[edit] Configurations

Most VSAT networks are 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,
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 HughesNet 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.