A satellite is a specialized wireless receiver/transmitter - essentially a radio-frequency repeater - that is launched by a rocket and placed in orbit around the earth. Today, there are literally hundreds of commercial satellites in operation around the world. These satellites are used for such diverse purposes as wide-area network communication, weather forecasting, television broadcasting, amateur radio communications, Internet access and the Global Positioning System.

The first man-made satellite, which was about the size of a basketball, was launched by the Soviet Union in the late 1950s. It did nothing but repeatedly transmit a simple Morse code signal back to earth. Since that time, satellites have become much more powerful.

Most communication satellites in use today are geostationary. They orbit the earth directly over the equator, approximately 22 000 miles (35 400 km) up. At this altitude, one complete trip around the earth (relative to the sun) takes 24 hours. Thus, the satellite remains over the same spot on the surface of the earth (geo) at all times, and stays fixed in the sky (stationary) from any point on the surface from which it can be "seen." A single geostationary satellite can "see" approximately 40 percent of the earth's surface. Three such satellites, spaced at equal intervals (120 angular degrees apart), can provide coverage of the entire civilized world.

A single transponder on one of these satellites (the part of the satellite that transmits signals back to Earth, of which a typical satellite has 32) is capable of handling approximately 100 million bits of information per second. This means that if the transponder is accessed for only 90 seconds per day, close to a billion bytes of data would be transferred - the equivalent of 865 000 double-spaced pages. With this immense capacity, today's communication satellites are an ideal medium for transmitting and receiving almost any kind of content, from simple data to the most complex and bandwidth-intensive video, audio and data content.

A very small aperture terminal (VSAT) is a device - known as an earth station - that is used to receive satellite transmissions. The "very small" component of the VSAT acronym refers to the size of the VSAT dish antenna -typically about 2 to 4 feet (0.55-1.2 m) in diameter- that is mounted on a roof on a wall, or placed on the ground. This antenna, along with the attached low-noise blocker or LNB (which receives satellite signals) and the transmitter (which sends signals) make up the VSAT outdoor unit (ODU), one of the two components of a VSAT earth station.

The second component of VSAT earth station is the indoor unit (IDU). The indoor unit is a small desktop box or PC that contains receiver and transmitter boards and an interface to communicate with the user's existing in-house equipment - LANs, servers, PCs, TVs, kiosks, etc. The indoor unit is connected to the outdoor unit with a pair of cables.

The key advantage of a VSAT earth station, versus a typical terrestrial network connection, is that VSATs are not limited by the reach of buried cable. A VSAT earth station can be placed anywhere - as long as it has an unobstructed view of the satellite. VSATs are capable of sending and receiving all sorts of video, data and audio content at the same high speed regardless of their distance from terrestrial switching offices and infrastructure.

A VSAT network has three components:

• A central hub (also called a master earth station)
• The satellite
• A virtually unlimited number of VSAT earth stations in various locations - across a country or continent

Content originates at the hub, which features a very large -15 to 36-foot (4,5 -11m)- antenna. The hub controls the network through a network management system (NMS) server, which allows a network operator to monitor and control all components of the network. The NMS operator can view, modify and download individual configuration information to the individual VSATs.

Outbound information (from the hub to the VSATs) is sent up to the communications satellite's transponder, which receives it, amplifies it and beams it back to earth for reception by the remote VSATs. The VSATs at the remote locations send information inbound (from the VSATs to the hub) via the same satellite transponder to the hub station.

This arrangement, where all network communication passes through the network's hub processor, is called a "star" configuration, with the hub station at the center of the star. One major advantage of this configuration is that there is virtually no limit on the number of remote VSATs that can be connected the hub. "Mesh" configurations also allow for direct communication between VSATs.

From major telecommunications providers to the United States Postal Service, businesses and governments around the globe have chosen to implement enterprise networks, telephony systems and broadband IP solutions based on the very small aperture terminal (VSAT) satellite technology.

Banks, SMEs, Universities, Internet Service Providers, air traffic controllers, insurance companies and other enterprises worldwide choose VSAT satellite networks for a number of key reasons:

• Ubiquitous availability
• Superior economics
• Reliability
• Multicast content distribution
• Timely deployment and installation
• Site relocation and addition
• Flexibility and expandability
• Network Capacity Expansion

Satellite is the only telephony and broadband wide-area network technology that is available everywhere - in even the most remote urban and rural areas, rain forests or concrete jungles, anywhere in the world. All that's needed is a clear view of the sky.

By contrast, other telephony and broadband technologies are strikingly limited in their coverage area. Terrestrial broadband technologies, such as DSL, Frame Relay, ISDN and cable reach only a small percentage of homes and businesses.

Telephony infrastructure - terrestrial copper and fiber optics, microwave, radio, wireless and underground cable - is also extremely restricted when compared to the virtually limitless reach of satellite technology. Satellite overcomes terrestrial limitations to provide these essential services to remote communities and businesses around the globe.

Satellite networks are much less costly to deploy, maintain and operate than terrestrial network technologies. Terrestrial networks require heavy infrastructure, whether they are telephony networks (based on copper wiring, fiber optic cables, radio or microwave towers), or broadband data networks (such as Frame Relay, DSL, ISDN and cable). High overhead costs for these infrastructures are passed on to the customer. In remote areas where such infrastructure does not exist, the expense of building such networks is often prohibitive, in developing and developed countries alike.

The economics of a satellite network are much simpler. The individual VSAT units are relatively inexpensive (about the same cost as a router in a Frame Relay network) and can be quickly and easily installed by a field technician. Hub and satellite costs are shared among thousands of customer sites, so the per-site cost of equipment, maintenance and management is low - and gets lower as more sites are added to the network.

And no terrestrial infrastructure development is ever needed. In fact, VSATs - which are built for low power consumption - can even run without electricity, using simple solar panels.

Satellite networks provide unmatched reliability, with far fewer potential points of failure than terrestrial solutions and built-in redundancy at almost every level to limit service interruptions when problems do occur.

Terrestrial networks have multiple potential points of failure where outages can occur: construction projects digging up streets; falling trees taking down telephone poles; equipment failures at the local telephone central office, to name a few. And many times, terrestrial network providers may not be able to fix these outages without third-party carriers.

Satellite networks have just three potential points of failure, each with built-in redundancy and back-ups: the satellite, the hub and the VSAT. Satellite outages are exceedingly rare but, should one occur, it is usually possible to automatically reroute traffic to back-up transponders without impacting service.

In the even more remote case of total satellite failure - which has occurred just twice in the 30-plus years that satellites have been in commercial use - back-up capacity is available on dozens of satellites. At the hub, online redundant equipment is used to provide immediate switching for uninterrupted service in the event of equipment failure. And VSAT equipment has the longest mean-time-between-failure in the industry: about 10 years.

Satellite's inherent strengths as a broadcast medium makes VSAT networks ideal for the distribution of bandwidth-intensive information - data, video or audio - to large numbers of remote locations.

To send a file to 1,000 recipients over a terrestrial network requires sending 1,000 separate and identical messages, each of which consumes valuable bandwidth and server resources. They are also likely to arrive at different locations at different times.

Satellite IP multicasting, on the other hand, can simultaneously deliver content to a virtually unlimited number of end-user locations - at speeds up to 40 Mbps. By eliminating duplicate transmissions, multicast technology maximizes the efficiency of existing servers and networks, and frees up valuable bandwidth.

Satellite networks can be rolled out to hundreds or thousands of locations in a fraction of the time required for a comparable terrestrial network.

With a terrestrial network, deployment and installation of new systems or even single locations is complicated, often involving multiple vendors who have no incentive to work with or assist each other. But VSAT technology is almost completely free of terrestrial infrastructure, so there is no need for coordination with any third party. With a satellite network, installation and deployment are quick and simple.

A STL installation team can usually complete a site install in a matter of hours, no matter where the site is located, meaning that complete network deployment to hundreds of sites can be accomplished in a matter of weeks, rather than months.

Relocating and adding network sites is significantly less complicated and less expensive with a satellite network than with most terrestrial technologies.

In the terrestrial world, vendors require advance notice to move a site; they may be unwilling or unable to fulfill requests for quick relocations, or charge significant extra fees. Adding a new location can be similarly complex and costly, in addition to incurring increased monthly bandwidth fees and other charges. In either case, the time and expense required increases significantly if infrastructure is not already in place - which is very often the case in remote and rural areas.

With a satellite network, installation of new sites takes just a few hours. Relocation can occur on the same day, in most cases, if the sites are close to one another. And no additional terrestrial infrastructure is ever required.

STL's VSAT technology has an unmatched ability to support a wide range of devices and applications. Single platforms can provide voice, fax, data and Internet connectivity; data networks can support advanced functions including IP multicasting.

STL's modular product design also allows for maximum scalability and fast upgrades - with an ease and simplicity not possible with terrestrial networks.

And satellite technology - with its unique broadcast and multicast capabilities - is the only choice for companies planning video and high-bandwidth content distribution as part of their wide-area network future.

Satellite technology provides a uniquely convenient environment for accommodating network and bandwidth expansion.

Indeed, one of the biggest wide-area network challenges is the ever-increasing need for additional bandwidth to support new applications. In a terrestrial environment this is especially challenging since, if a new application is large enough, new terminal components (routers, cards, etc.) have to be ordered - and increased bandwidth has to be commissioned - separately at each site, in conjunction with local third-party vendors. In many cases, the cost of expanding network capacity on a terrestrial network can actually exceed the original cost of deploying the network. Plus, such an upgrade, if economically feasible, can take months, since new circuits have to be ordered and a field technician must visit every site.

With a satellite network, network expansion is extremely easy and comparatively inexpensive. First, all bandwidth allocation is controlled at the hub, so increasing network capacity is as simple as increasing the amount of bandwidth allocated to the network. And, while in some cases additional equipment may be required at the hub to support the increased capacity, this hardware can most often be installed in a matter of days. More importantly, no hardware changes or field technician visits are required at the remote sites, since STL's VSAT equipment is designed out of the box to handle maximum bandwidth requirements.