Tuesday, August 12, 2008

This employs a satellite in geostationary orbit to relay data from the satellite company to each customer. Satellite Internet


This employs a satellite in geostationary orbit to relay 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 only compete with cellular broadband. However, costs have been coming down in recent years to the point that it is becoming more competitive with other broadband options. German ISP, Filiago, offers the ASTRA2Connect satellite Internet system for €320 (equipment) plus €100 (registration) and a flat rate monthly fee dependent on bandwidth - from €20 for 256Kbit/s download, 64Kbits/s upload, to €80 for 2048Kbit/s download, 128Kbits/s upload.

Satellite Internet also has a high latency problem caused by the signal having to travel 35,000 km (22,000 miles) out into space to the satellite 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 multiplayer Internet games and first-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. These problems are more than tolerable for just basic email access and web browsing and in most cases are barely noticeable.

There is no simple way to get around this problem. The delay is primarily due to the speed of light being 300,000 km/second (186,000 miles per second). Even if all other signaling delays could be eliminated it still takes the electromagnetic wave 233 milliseconds to travel from ground to the satellite and back to the ground, a total of 70,000 km (44,000 miles) to travel from the user to the satellite company.

Since the satellite is usually being used for two-way communications, the total distance increases to 140,000 km (88,000 miles), which takes a radio wave 466 ms to travel. Factoring in normal delays from other network sources gives a typical connection latency of 500-700 ms. This is far worse latency than even most dial-up modem users' experience, at typically only 150-200 ms total latency.

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.

Advantages

True global broadband Internet access availability
Mobile connection to the Internet (with some providers)
Disadvantages

High latency compared to other broadband services, especially 2-way satellite service
Unreliable: drop-outs are common during travel, inclement weather, and during sunspot activity
The narrow-beam highly directional antenna must be accurately pointed to the satellite orbiting overhead
The Fair Access Policy limits heavy usage, if applied by the service provider
VPN use is discouraged, problematic, and/or restricted with satellite broadband, although available at a price
One-way satellite service requires the use of a modem or other data uplink connection
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.

No comments: