The word modem means modulator or demodulator. Satellite modems transform and receive an input bit stream to a radio signal. However, some satellite modem devices only have a demodulator that is used to access satellite Internet, whereas data is transferred in other directions via the use of a conventional PSTN model or an ADSL modem. Internet service provided via satellite is not connected through telephone lines or cable systems. In contrast, a satellite dish is used for two-way (upload/download) data exchanges. The upload speed via a satellite dish is approximately one-tenth of the 500 kbps download speed. Consumers with DSL and cable connections benefit from having higher download speeds in comparison to satellite. However, satellite connections are approximately ten times faster in operation than a normal modem. There are several companies that may provide two-way satellite Internet services. These companies include Pegasus Express, Teledesic, StarBand and Tachyon. The Pegasus company satellite Internet service is actually the two-way version of DirecPC. Tachyon offers two-way satellite Internet in Western Europe, Mexico, and the United States. When installing a satellite modem, there must be a clear view to the south. This is a necessary requirement because the orbiting satellites are located over the equator region. Heavy rains and tall trees affect the reception of both Internet signals and satellite TV signals. Two-way satellite Internet modems work by using Internet Protocol (IP) multicasting technology. Approximately 5,000 channels of data exchange can concurrently be supplied by one solitary satellite. Data is sent in a compressed format from one point to numerous other points, simultaneously, through IP multicasting. Compressing the data decreases the data size and the bandwidth. Regular land-based, dial-up global systems are limited and prevent multicasting on this scale. However there are some satellite services that necessitate a consumer to have either a cable modem connection or a dial-up connection to facilitate the data sent to the Internet. The satellite transmits data to the computer through the same satellite dish connection that facilitates pay-per-view television programming.
