Satellite broadband

Satellites in geostationary orbits are able to relay broadband data from the satellite company to each customer. Satellite Internet is usually among the most expensive ways of gaining broadband Internet access, but in rural areas it may be the only choice other than cellular broadband. However, costs have been coming down in recent years to the point that it is becoming more competitive with other broadband options.

Broadband satellite Internet also has a high latency problem is due to the signal having to travel to an altitude of 35,786 km (22,236 mi) above sea level (from the equator) out into space to a satellite in geostationary orbit and back to Earth again. The signal delay can be as much as 500 milliseconds to 900 milliseconds, which makes this service unsuitable for applications requiring real-time user input such as certain multiplayerfirst-person shooters played over the connection. Despite this, it is still possible for many games to be played, but the scope is limited to real-time strategy or turn-based games. The functionality of live interactive access to a distant computer can also be subject to the problems caused by high latency. Additionally, some satellite Internet providers do not support VPN due to latency issues^[6]. These problems are more than tolerable for just basic email access and web browsing and in most cases are barely noticeable. Internet games and

For geostationary satellites there is no way to eliminate this problem. The delay is primarily due to the great distances travelled which, even at the speed of light (about 300,000 km/s or 186,000 miles per second), can be significant. Even if all other signalling delays could be eliminated it still takes electromagnetic radio waves about 500 milliseconds, or half a second, to travel from ground level to the satellite and back to the ground, a total of over 71,400 km (44,366 mi) to travel from the source to the destination, and over 143,000 km (88,856 mi) for a round trip (user to ISP, and then back to user—with zero network delays). Factoring in other normal delays from network sources gives a typical one-way connection latency of 500–700 ms from the user to the ISP, or about 1,000–1,400 milliseconds latency for the total Round Trip Time (RTT) back to the user. This is far worse than most dial-up modem users' experience, at typically only 150–200 ms total latency.

Medium Earth Orbit (MEO) and Low Earth Orbit (LEO) satellites however do not have such great delays. The current LEO constellations of Globalstar and Iridium satellites have delays of less than 40 ms round trip, but their throughput is less than broadband at 64 kbit/s per channel. The Globalstar constellation orbits 1,420 km above the earth and Iridium orbits at 670 km altitude. The proposed O3b Networks MEO constellation scheduled for deployment in 2010 would orbit at 8,062 km, with RTT latency of approximately 125 ms. The proposed new network is also designed for much higher throughput with links well in excess of 1 Gbps (Giga bits per second).

Most satellite Internet providers also have a FAP (Fair Access Policy). Perhaps one of the largest disadvantages of satellite Internet, these FAPs usually throttle a user's throughput to dial-up data rates after a certain "invisible wall" is hit (usually around 200 MB a day). This FAP usually lasts for 24 hours after the wall is hit, and a user's throughput is restored to whatever tier they paid for. This makes bandwidth-intensive activities nearly impossible to complete in a reasonable amount of time (examples include P2P and newsgroup binary downloading).

The European ASTRA2Connect system has a FAP based on a monthly limit of 2Gbyte of data downloaded, with download data rates reduced for the remainder of the month if the limit is exceeded. Other Satellite Internet offers have advanced FAP mechanisms based on sliding time windows. It is the case for instance for the Tooway service that verifies download quotas during the last hours, days and weeks. The purpose is to allow temporary excessive downloads when needed while saving volume for the end of the month.

Advantages

1. True global broadband Internet access availability
2. Mobile connection to the Internet (with some providers)

Disadvantages

1. High latency compared to other broadband services, especially 2-way satellite service
2. Unreliable: drop-outs are common during travel, inclement weather, and during sunspot activity
3. The narrow-beam highly directional antenna must be accurately pointed to the satellite orbiting overhead
4. The Fair Access Policy limits heavy usage, if applied by the service provider
5. VPN use is discouraged, problematic, and/or restricted with satellite broadband, although available at a price
6. One-way satellite service requires the use of a modem or other data uplink connection
7. Satellite dishes are very large. Although most of them employ plastic to reduce weight, they are typically between 80 and 120 cm (30 to 48 inches) in diameter.

Source from : Wikipedia