Satellites once top-secret devices, were used primarily in a military capacity, for activities such as navigation and espionage. Now they are an essential part of our daily lives. Besides other services, Satellite Internet service is becoming more and more popular, now thousands of people have an extra dish on the home or RV. Part of the reason for this is that certain technologies have increased the bandwidth and decreased the cost.
Now, there are geostationary satellites. These satellite stays still in relation to a fixed position on Earth. The latest way to communicate with satellites for Internet service is over something called the Ka band. The Ka band is a set of frequencies that are between 18.3 GHz and 31 GHz. More specifically, the uplink (that part of the call that is going from your home to the satellite) is in the range of 27.5 GHz and 31 GHz. The downlink (that part of the call that is coming from the satellite to your home) is in the range of 18.3 Ghz and 20.2 Ghz. For those of you who don’t know, the lower frequencies transmit longer distances with less power, but aren’t capable of carrying a lot of information.
Because of the high frequency rates, that signal has to be stepped down and lose a bit of power before it hits our Computer. This is done using a device that is on the dish itself as well as having a minimum of 150 feet of high-quality RG6 coax cable connecting the dish to PC. Something else you should know about is that Ka band satellite uses spot beams. A spot beam covers a specific area that really isn’t that big – about a third the size of Alberta. Each spot beam can support only so many users. You can’t move your service from spot beam to spot beam unless you are a certified installer. You will also need a clear line of sight to the satellite.
The data travels from the satellite equipment at the customers location to the satellite, and then to the teleport for routing to the Internet. Teleport is a secure facility where many large aperture satellite dishes are operated and is connected to Network Operations Center (NOC).At the NOC, routers are connected to the Internet. Proprietary acceleration and advanced spoofing technology is employed to provide IP transparency and increase throughput speed. Spoofing is what makes the service capable of very high speeds.
Why is spoofing important? The entire Internet is based on TCP/IP. TCP (Transmission Control Protocol) manages and controls transmissions using IP (Internet Protocol). TCP sends data and looks for acknowledgments (receipts) sent back from the receiving end to indicate that everything was received. Because of the long round-trip (90,000+ miles) that the packets must travel over the satellite link and back, the acknowledgments are delayed by several hundred milliseconds. If uncorrected, this delay would cause TCP to throttle back its speed dramatically.
Spoofing is accomplished by special NOC equipment (Hybrid Gateway) that causes TCP acknowledgments to be returned to the sender very quickly. It does this by spoofing (pretending to be the remote site) and acknowledging the packets instantly, at the same time as it forwards the packets to the remote site. TCP sees rapid acknowledgments and therefore ramps up its speed quickly. The Hybrid Gateway also looks for the real acknowledgments and discards them. If an acknowledgment is missed, the Hybrid Gateway resends the packet from its buffer. It is in this manner that multi-megabit speeds are made possible over satellite.
In Satellite Internet its important to know latency and Fair Access Policy. Latency is the time when your signal is going between your house and the satellite. Typically, it’s about 230 milliseconds or more. That doesn’t seem like much considering the signal is covering about 45,000 miles in that time. However, when it comes to things like VoIP or online gaming, it makes it nearly impossible to do.Fair Access Policy or FAP is the limit that your Stellite Internet Service Provider will put on how much you can download over a period of time, usually 24 hours. If you exceed that, they will automatically slow your speed down to something close to dial-up, to give other users fair access to the satellite. So, if you are a chronic downloader, you’ll have to change your ways for satellite Internet.
All this for about $800 for the hardware and $50 a month for ongoing service. Not bad, when you consider bringing in a phone line down a logging road will cost about $10,000 a pole. However, if you want to put a self-pointing dish on your RV, you’re going to need to dig a little deeper as the hardware will run you about $10,000. You could try to take a stationary dish with you, but pointing the new dishes can take up to eight-hours to aim, and you must be a certified installer.
Source : Author, Guy McDowell, Vsat Systems
