About VSAT

Connecting the dots:

Do you need to get data from one place to another? How about tying a large number locations together into one large data network? What about broadcasting video, audio, or even widespread distribution of data to many locations simultaneously?

If you need to do one or more of the above, you might consider the possibility of using VSAT.

VSAT stands for Very Small Aperture Terminal. What does that mean? Simply put, it means "Satellite communications using a small dish." How small? Depending on a number of parameters, the dish could be as small as 3 feet and is typically 4 to 6 feet. VSAT applications can be receive-only or transmit-receive (i.e. bi-directional.)

Taking the receive-only case for a moment, here are but a few of the possibilities:

When you add transmit capability to the mix, there are even more possibilities:

These are but a few examples of what is currently being done via VSAT - but this list isn't all-inclusive: We are constantly amazed at the number of new applications that people come up with for VSAT.

What are the advantages of VSAT?

VSAT is inherently a broadcast oriented methodology. That is, if you have a large population of remote locations that you are connecting as a common network (such as gas stations, retail locations, etc.) VSAT can really shine. How large is "large?" Let's say, a couple dozen. VSAT, like many other technologies, can become a more attractive option as it is scaled larger - getting the the point where it can be a far less expensive networking alternative than terrestrial based systems.

VSAT has another property that can be used to advantage: It can be used to broadcast large amounts of data to as many sites are receiving it. This could be useful for distributing files, executables, operating system upgrades, audio, or even video. Doing this sort of operation can be tricky using land based technologies such as Frame Relay or other terrestrial internet connections: In the case of these two methodologies, a large data transfer can saturate a network, cause congestion and packet loss - interrupting the normal data flow as well as requiring a lot of retransmissions.

With reference to the "file broadcast" methodology mentioned above, what about packet loss over the Satellite? As it turns out, Satellite connections are very reliable and predictable. If, for some reason a packet is lost in a "data broadcast" there are at least two ways to get the missing data:

VSAT is considered to be a "reliable" connection: That is, if you put a packet in one end, it is guaranteed to come out the other end. This is not always the case with a Frame Relay or Internet connection where stuffing a packet in one end of the network does not guarantee its "safe transport" to the destination. If a packet is lost on these networks, it is up to the end devices to make sure integrity is maintained. These "retransmissions" can result during network congestion - and they always slow the pace of the data transfer.

Data entering a VSAT network, on the other hand, does not necessarily go into a mysterious "cloud" - and, like a terrestrial network, "hopefully" appear intact on the other side on the first transmission. Being a more limited-scope network, it is possible to have very tight control of what sort of applications run on that network, when, and for how long. Because of this, traffic profiling is practical and more control can be given to making sure you don't have too much (more cost) or too little (poor performance) capacity. Because the VSAT itself guarantees reliable data transfer, slowdowns due to retransmissions can be minimized.

There is one additional possible advantage with VSAT that may not be too obvious: statistical multiplexing. Many applications require throughput that is not consistent and varies throughout the day - depending on, say, customer activity in a retail environment. If, for example, you have locations spread across a large geographical area, peaks in customer activity will not occur everywhere simultaneously. In this case, the network should be sized so that it can handle the expected peak aggregate load. In a terrestrial circuit, it is more difficult to spread this statistical advantage over a large geographic area: Your individual circuits must be sized to handle the highest peaks - even if those peaks occur for only short times over the course of a day. What this means is that you must have a much higher potential capacity (when all sites are considered) than you will actually ever use - which means increased cost.

Finally, A VSAT network does not rely on terrestrial data circuits: If there is a large "local" (to the remote site) network outage due to a cable cut, telco failure, or natural disaster, service is unaffected. As long as there is electrical power, service can be maintained. Because it does not rely on telco circuits, it can be placed nearly anywhere where a view toward the southern sky is possible - and done quickly. With the system being self-contained, repair and maintenance may be done expeditiously.

What are the disadvantages of VSAT?

VSAT is not without its drawbacks - and these should be considered in the system design:

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