Satellite Communications - WAN Optimization
Satellite Communications started on October 4, 1957 when the Soviets launched Sputnik. It had a radio transmitter that had two frequencies 20.005 and 40.002 MHz. A year later the first American satellite to relay communications used a tape recorder to store and forward voice messages. In the 1990s the Internet started to use broadband satellite communication technology.
Satellite Internet
Rural areas and areas still under development that don’t have access to DSL or cable can connect to the internet via satellite. High speed satellite Internet allows people to download information from the Internet at DSL speeds. High speed satellite Internet allows companies and private consumers to stay connected where no other high speed connections exits. Most high speed Internet requires a satellite dish to be mounted on the roof and a modem.
Satellite internet service comes in one-way and two-way. One-way satellite service requires a dial up modem to send information to the Internet then the satellite is used to download data. Two-way satellite internet doesn’t require a modem and sends and receives data using the satellite.
Satellites in Geostationary Orbit
Most communication satellites are in geostationary orbit about 22,000 miles from earth. Satellites in geostationary orbit use microwaves to communicate with the earth. It takes approximately 125 ms for a microwave to travel from earth to the satellite and another 125 ms for the signal to reach earth. This quarter second delay makes geostationary satellites inadequate for time sensitive applications without optimization. Typical latency for a satellite connection is between 500 and 700 ms from the user to the Internet service provider and round-trip time is between 1,000 and 1,400ms. Dial up by comparison is typically between 150 and 200ms total delay. Geostationary orbit is preferred because it doesn’t move in relation to the earth. This allows fixed satellite dishes to be pointed at the satellite. Geostationary satellites offer higher data speeds then low Earth orbit satellites. Geostationary satellites are not in the line of sight of Polar Regions preventing communication with the North and South Polls.
Satellites in Low Earth Orbit
Current low earth orbit satellites have a delay of less than 40 ms round trip but have lower data speeds than broadband. These low orbit satellites are between 416 and 882 miles from the earth. 78 New low earth satellites expected to launch in 2015 will be 621 miles from the earth, have speeds up to 12 gigabits per second and cover 100% of the earth’s surface.
Satellites in Medium Earth Orbit
Medium earth orbit satellites are approximately 4970 miles from earth. New medium earth orbit satellites expected to be launched in 2013 will have a round trip time of 125ms and gigabit throughput. Medium earth orbit satellites will be able to provide billions of people around the world with low latency high speed internet access.
Common Satellite Internet Issues
Satellite communications are susceptible to rain fade. Rain fade is caused by precipitation such as rain and snow. Low frequency bands are not as susceptible to rain fade as higher frequencies so lower frequencies are used for tropical regions. Larger dishes can also help to reduce the effects of rain fade.
The Consultative Committee for Space has created SCPS (Space Communications Protocol Stack) to work in extreme conditions. SCPS included new protocols that help to improve satellite communications. These protocols include SCPS-FP file protocol, SCPS-TP retransmission control protocol, SCPS-SP security protocol and SCPS-NP Network protocol. Optimization techniques such as TCP acceleration, HTTP pre-fetching and DNS caching can help to reduce problems cause by satellite latency. Ad-blocking software can also help to reduce latency by eliminate cache busting used by advertising web sites to maximize the number of ad views seen.
Satellite Internet requires encryption in order to keep data private. Without encryption anyone with a satellite receiver would be able to view your data.
Satellite Summary
Geostationary satellites provide inexpensive high speed Internet to people in rural and developing areas. Because geostationary satellites are so far away from earth optimization is needed to help reduce latency. In the near future new low and medium orbit satellites will replace geostationary satellites. Latency is reduced when using low and medium orbiting satellites because the microwave signal doesn’t have to travel as far. Medium and low level orbiting satellites can also reach areas that geostationary satellites can’t making it possible to get high speed internet in extremely remote regions including the North and South Pole.
