Hardware

Implementing satellite-based Internet access

Many have to turn to nonstandard methods when choosing a high-speed Internet access service. One such service is satellite-based. Unfortunately, satellite-based connections are quirky. Brien Posey is here to explain those quirks.


Recently, I made a decision to move out of state. After buying a house, I found out that there were no cost-effective types of broadband Internet connections available (such as ADSL or cable modems). Because a T-1 line wasn’t in the budget and a dial-up connection was just too slow, I realized that I had to find another method of Internet access. After doing some research, I decided to use a satellite modem for my Internet access. However, the process wasn’t easy. There are a lot of issues to consider when deciding whether or not a satellite modem will be a feasible option for you.

In this Daily Drill Down, I’ll explain some of the hurdles that you’ll have to deal with when implementing satellite-based Internet access.

An introduction to satellite communications
As I mentioned, before you can implement satellite-based Internet access, there are a few hurdles that you must get around. In my particular situation, some of the biggest hurdles were related to the satellite modem itself. A satellite modem works very differently from a DSL or cable modem. One of the differences is that many satellite modems offer only unidirectional communications. This means that Web pages can be received through your satellite dish, but you can’t use the satellite modem to do things like send e-mail messages or request a Web page. Instead, outbound communications go through a traditional analog modem, while inbound communications are received through the satellite modem. This raises several issues.

In my introduction, I compared satellite-based communications with other forms of broadband communications. However, this isn’t really a fair comparison. One reason is that consumer-grade satellite modems are much slower than other forms of broadband communications. For example, my present DSL connection runs at 1.5 megabits per second. A typical consumer-grade satellite modem can receive data at speeds of around 400 to 500 kilobits per second. As you can see, these speeds are about three times slower than my present Internet connection. Satellite modem speed looks even worse when you consider that in some areas DSL speeds approach 4 megabits per second. Consumer-grade satellite modems are faster than ISDN modems though (which are usually limited to 128 kilobits per second), and the Internet services usually cost less.

Consumer vs. commercial-grade modems
You may be wondering what the difference is between consumer-grade satellite modems and commercial-grade satellite modems. Commercial-grade satellite modems usually offer higher bandwidth but at a cost—a big cost. Commercial-grade satellite modems typically require large dishes and have outrageously expensive connect fees. In addition to a monthly service fee, many commercial-grade satellite providers charge a few cents for every megabit of data that passes through the satellite. Because of the high costs associated with commercial-grade satellite systems, I’ll limit the remainder of my discussion to consumer-grade systems.

I mentioned earlier that consumer-grade satellite modems are slower than other forms of broadband communications, receiving data at a mere 400 to 500 kilobits per second. However, these communications are actually slower than they might first appear. Consider the case of a system that relies on an analog modem to send data and a satellite modem to receive data. On such a system, the maximum speed of outbound data would be 56 kilobits per second, while the maximum speed of inbound data would be around 400 kilobits per second. However, these speeds are deceptive. While data can theoretically flow at these speeds, there are a number of factors that slow communications. For example, phone line quality plays a big part in the outbound data speed, as does how busy your Internet service provider happens to be at the moment. The primary factor affecting inbound data is the weather. If it’s raining, snowing, etc., satellite communications can become impaired and may require a number of retries.

The nature of satellite communications
The biggest factor slowing the data speed is the very nature of satellite communications. Suppose for a moment that you attempt to access a favorite Web page. When you enter the page’s URL, the URL is sent to your Internet service provider, not to your satellite provider. The packets containing the URL that you entered must then be routed from your Internet service provider to your satellite provider. To accomplish this routing, the packet is encapsulated and combined with header data that forces your Internet service provider to pass the packet to the satellite service provider.

As you can see, the encapsulation process adds several bytes to each packet. However, since TCP/IP packets have a maximum byte size, each packet carries less data than normal in order to make room for the routing information. This means that if you sent the exact same e-mail message from a traditional Internet client and from a satellite-based Internet client, the satellite-based client would have to send more packets than the traditional client to get the job done. Therefore, as you can see, when looking at the speed of a satellite modem, you must also consider any additional overhead that you’ll encounter.

You may be wondering what happens to your packets after they’re routed to the satellite provider. When the satellite provider receives your packets, the encapsulation data is stripped away, leaving your original data (in this case, a URL). The satellite provider then sends a request over land-based lines to get the Web page you asked for. Once the satellite provider has received the requested Web page, it transmits the page to the satellite, along with some information regarding which satellite modem the page is destined for. The satellite then transmits this information to all of the subscribers. Every subscriber receives the page that you requested. However, since the page was transmitted along with some identifying criteria, such as the serial number of your satellite modem, every satellite modem except yours ignores the inbound Web page. As you can see, this type of satellite communications is complicated and has a lot of overhead.

Proxy server issues
In my case, I didn’t like the slow speeds offered by satellite modems but at least it was faster than dial-up. My biggest problem is that, presently, my DSL modem is connected to a proxy server. The proxy server acts as a firewall and also makes Internet access available to all of the PCs on my network. Although a proxy server can be configured to work with a dial-up Internet connection, I wanted to have the “always on” Internet access that I’ve grown accustomed to. Fortunately, I was able to find a satellite modem that was capable of sending and receiving data without using a dial-up connection. I’ll explain more about this later. However, this brought up another issue.

Modems and Microsoft
The two different types of satellite modems that I had considered using were USB-based. Unfortunately, Proxy Server was designed to run on Windows NT Server 4.0, which doesn’t support USB. My DSL modem simply plugged into a network card on the server. It was then necessary to either find a way to make Proxy Server run under Windows 2000 Server or to upgrade the server to Windows 2000 and then install Internet Security and Acceleration Server 2000. Fortunately, I was able to find a patch that would allow me to run Proxy Server on a Windows 2000 Server. You can acquire the patch from the Microsoft site.

Once I had chosen a satellite provider and figured out how to make the satellite modem work with my existing network, there was only one more major hurdle to clear. As you may know, satellite dishes require a direct line of sight with the satellite. In English, this means that you can’t have any trees, mountains, buildings, or anything else standing between your satellite dish and the satellite. Therefore, before investing in a satellite modem kit, it’s necessary to determine whether or not you’ve got a clear view of the correct portion of the sky.

Locating the satellite
Figuring out where the satellite is in the sky can be a little tricky. To do so, you have to calculate the satellite’s azimuth and elevation. The azimuth is basically a fancy word meaning the satellite’s horizontal position based on compass headings. The elevation is the satellite’s vertical position in the sky, measured in degrees.

To calculate the azimuth, you need to know the satellite’s geographic location. The best way to find this is to check with the satellite provider and ask them where the satellite is located. The types of satellites that are used for Internet access maintain a geosynchronous orbit. This means that they remain in the exact same spot in the sky at all times. To accomplish a geosynchronous orbit, a satellite must be placed at about 22,300 miles directly above the equator. At this altitude over the equator, the satellite’s orbit time is 24 hours. Therefore, because the earth rotates on its axis every 24 hours and the satellite takes 24 hours to complete one earth orbit, the satellite appears to be a stationary object in the sky (even though it’s actually moving at about 17,600 mph).

So what does this mean to you? First, it means that if you live in North America, you know that you’ll be looking for the satellite somewhere in the southern sky, since the satellite is located above the equator. Since you know that the satellite orbits above the equator, you know that its latitude is 0. You can get the longitude from the satellite provider. By getting this information, it’s possible to mark on a map the exact position where the satellite orbits above.

Once you’ve marked the satellite’s position on a map, you’ll need to mark your position on the map, as well. Now, draw a straight line between the two points and measure the angle of the line as compared with due south. For example, the Star Band satellite is located at 101 degrees west latitude, 0 degrees longitude. From my home in South Carolina, the measured angle was about 28 degrees west of due south. Since due south is at a compass heading of 180 degrees, you’d add the 28 degrees to it to give you a compass heading of 208 degrees. This means that from my home, the Star Band satellite is located somewhere in the sky above the 208 degree compass heading.

In this particular example, the satellite existed at 101 degrees west longitude, which is directly south of Texas. However, suppose that you were in a western state, such as California, instead of being on the East Coast. In such a case, you’d still calculate the angle of the path from your location to the satellite’s location. However, rather than adding the angle to the 180 degree due south mark, you’d subtract the angle from 180 degrees. While all of this sounds complicated, it’s really quite simple. If you were to the east of the satellite, you’d add the angle to 180, but if you were to the west of the satellite, you’d subtract the angle from 180.

Conclusion
High-speed Internet connectivity can be had even in the remotest of locations—if you have a little patience and some basic math skills. For more information on satellite connectivity, take a look at these sites:
  • Helius: Products and technologies for satellite broadband solutions
  • StarBand: Consumer two-way, always-on, high-speed satellite Internet service provider
  • Cidera: Offers a fully-operational Internet transport solution via satellite

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