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Satellite Internet: How It Works

VSAT Systems uses a satellite connection as a high-speed digital link between a customers location and the US Internet backbone. The data travels from the satellite equipment at the customers location to the satellite, and then to the teleport for routing to the Internet.

The teleport is a secure facility where many large aperture satellite dishes are operated. The SES Americom operations center is located at the teleport and our equipment is located in a leased area inside the Network Operations Center (NOC).

satellite internet how it works diagram

At the NOC, routers are connected to the Internet using OC-3 optical connections to a Tier-I Internet backbone provider.

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. If the acknowledgments are not received, TCP resends the packets and slows down its transmission speed for future data. TCP expects these acknowledgments to be received within a certain time frame. 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.


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