Networking

Is your company ready for a satellite-based WAN connection?

A great deal of progress has been made in making satellite communications more efficient, more secure, and more reliable. These improvements may make satellite communications ideal for some Net Admins who never would have considered it before.


WAN connections have been around for quite some time, but, lately, it seems as though wireless WAN connections are gaining in popularity. There are certain situations in which a wireless WAN connection is a lot less expensive than a traditional wired connection. Furthermore, wireless connections can also be used to reach very remote areas where a wired connection is simply out of the question. Of course, even wireless connections have their limits. This is where satellite connections come in. Satellite connections offer connectivity anywhere in the world. Unfortunately, satellite connections have long been plagued by security, cost, and throughput issues that make satellite-based WAN connections less than desirable. In this article, I will discuss how satellite connections are coming of age and why a satellite-based WAN connection might be ideal for some enterprise-class organizations.

The problems (and their solutions) with satellite WAN
In the short history of satellite-based WAN connections, there have been three major problems that have often driven corporations to find alternative solutions. These problems are cost, security, and latency/throughput. However, some new technologies are helping to address these three issues and are making satellite-based WAN links more practical.

Security
Any time that you are transmitting data through the air, where anyone can receive it, security is a concern. However, many of the satellite-based WAN connections have begun to function in the same way as a terrestrial VPN connection. Packets are transmitted by using the TCP protocol but are encrypted with L2TP, IPSec, or a number of other encryption protocols.

Cost
The cost of satellite communications can be staggering. Typically, a single satellite has enough capacity to serve many customers. Customers are billed based on the amount of bandwidth used or on the amount of time that they are connected to the satellite.

One of the ways that customers are cutting satellite costs is by not using a health check packet. On terrestrial links, it's common to send frequent packets whose sole purpose is to make sure that the link is still connected. With a satellite system, though, these packets cost money. As an alternative, some customers are adopting technologies that drop the link completely when there is no "real data" to transmit. During these down times, the customer is not being billed, because they are not connected to the satellite.

Throughput
Throughput and latency are definite concerns when dealing with satellite communications. Satellites often have a latency of several seconds. So where does this latency come from? As you may know, data is transmitted to and from a satellite at the speed of light, or 186,000 miles per second. At this speed, you would think that the data would have a very fast trip to the satellite and back. However, satellites are further away than most people realize.

For a communications satellite to work, it must be placed in a geosynchronous orbit (sometimes called a geostationary orbit). This means that the satellite stays at the same position in the sky. You have probably heard that space shuttle astronauts orbit the earth once every 90 minutes. This is true because orbital velocity is 17,600 MPH. At an altitude of a couple hundred miles, an orbit of this velocity occurs in roughly 90 minutes.

Keep in mind that an object must sustain an orbital velocity to stay in space anywhere near the earth's proximity. If the object were to slow down below orbital velocity, it would be pulled back to earth by gravity and would burn up on reentry. Therefore, a satellite has to keep moving at about 17,600 miles per hour at all times. The only way a satellite is able to stay in a constant position in the sky is because the earth is rotating. If a satellite is launched to an altitude of 22,000 miles directly above the equator, then at 17,600 MPH, the satellite will be moving at the same speed at which the earth turns, and it will stay over the exact same portion of the earth.

Obviously, there is a huge distance that the signal has to travel. The latency is caused because the signal has to travel from the sender to the satellite and then from the satellite to the receiver. Furthermore, depending on the distance between the sender and the receiver, the signal may have to be relayed to other satellites prior to being relayed to the receiver.

So what can you do about this latency? Not a thing. You can't make a signal travel any faster than the speed of light and you can't bring the satellite any closer. What you can do, though, is increase the throughput to the satellite. Increasing the throughput won't get rid of the latency, but it will make the entire communications process more efficient. For example, suppose that it normally takes seven seconds to get a packet from point A to point B. If you increase the throughput, it will still take seven seconds to move the packet, but you might be able to move three or four additional packets within that same time frame. The data itself isn't moving any faster; you are just transmitting and receiving more packets per second, giving the illusion that the data is traveling faster.

One of the primary techniques being used to increase throughput is compression. By compressing the data, it becomes possible to transmit more information within each packet. Compression relies on the sender having an encoder and the receiver having a decoder. Although the data is already encrypted, compressing it using a proprietary compression scheme provides further security because anyone who might intercept the data would first have to figure out how to decompress it before they could even begin to figure out how to decrypt it.

Another way that throughput is being increased is through packet regeneration. For example, let's pretend that the time it takes a receiver to get a packet is seven seconds from the time it was transmitted. Now suppose that a packet was lost in transit. It would normally take seven seconds for receivers to realize that they were missing the packet. The receiver would then have to tell the sender to retransmit the packet; the sender would then have to retransmit. If you don't factor in for processing time, this cycle would take 21 seconds to complete.

However, new protocols are building just enough information into packets that missing packets can be reconstructed rather than retransmitted. This means that if receivers receive an incomplete message, they can reconstruct the message on the fly rather than having to ask for the missing packet to be retransmitted.

Cheaper links
Compression and data regeneration technologies can also reduce an organization's overall cost as well. Remember that many satellite providers bill customers based on the amount of bandwidth consumed. Both of these technologies are aimed at transmitting fewer packets, resulting in a lower satellite bill.

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