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:
- Receive video and/or audio. This could be for music, corporate video, sales, promotion, or whatever.
- Receive data. This could include digitized video and/or audio (real-time or faster/slower than real-time) as well as raw data such as information feeds, or even distributions of large files (such as operating systems, executables, packages, etc.)
When you add transmit capability to the mix, there are even more possibilities:
- Point-of-sale ("POS")
- EFT (Electronic Funds Transfer) and credit/debit card verification
- Batch traffic (sales/inventory, for example)
- Internet access
- Voice telephony
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:
- Send the data broadcast more than once. Multiple "sendings" will take a lot less bandwidth than on a terrestrial network where, for each transfer to each site, a separate connection may need be established. It is unlikely that exactly the same information will be missing on each data broadcast. The receive end can "listen" to the broadcast and, when it "hears" a packet that it knows that it missed, it can fill-in the missing data.
- After the data broadcast(s) are done, request "fills." In this case, the remote sites would report which packets of data were missing and then, in a batch process, those pieces of data could be re-transmitted. Any sites missing the same pieces would hear this "fill-in" broadcast and would be able to receive those packets when they were sent.
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.
All you need is a source of power and some sky and we can
provide connectivity practically anywhere!
What are the disadvantages of VSAT?
VSAT is not without its drawbacks - and these should be considered in the system design:
- Latency. The speed of light being what it is, and the fact that the satellites are 23,000 miles above the equator, it takes the signal approximately 0.26 seconds to get to the satellite and back. This bit of delay can play havoc with certain types of applications. Some interactive applications (such as dumb terminal with remote echo) can be nearly unusable unless appropriate measures are taken. There are also non WAN-friendly applications out there (including ones that purport to be WAN-friendly) that require an inordinate number of data exchanges for even the most trivial of functions: It should be pointed out that these applications are typically poor candidates for any WAN application - be they terrestrial or otherwise.
- Occasional outages due to the sun. Twice a year, there are brief periods (lasting a few minutes) where the Sun moves directly inline with the satellite. The Sun, being a very powerful source of radio signals, temporarily jams the satellite signal. These outages can be predicted very precisely and last only a short time. (Most users can tolerate "scheduled" outages - it is those "unscheduled" ones that cause the most problem...)
- Occasional outages due to weather. Occasionally, very heavy precipitation will block the signal for short periods. These outages are fairly rare and don't normally last for more than a few minutes. Another possibility is that of snow building up in a dish, but proper system design (e.g. installation of covers, heaters, and occasional vigilance and, in a worst-case scenario, the use of a broom) can prevent such outages from ever happening in the first place.
- Failure of the Satellite itself. Fortunately, this is extremely rare. Satellites are some of the most reliable pieces of equipment made - and they are loaded with redundant systems. Even in the event of a failure, it is practical to restore service simply by pointing the antenna at a different satellite.
For further information, please feel free to contact us.
- You may send us email at
- You can call us at (801)-263-0519
- U.S. Satellite is located at:
935 West Bullion Street
Murray, UT 84123
U.S. Satellite Corporation does not actively market any products or services directly to the consumer. If you have ever received any solicitations for products or services by a company representing itself as "U.S. Satellite Corporation" please contact us immediately to inform us of such unauthorized use of our trademark.