Signal Latency: A Satellite Internet Limitation

Signal latency is the delay between requesting data and the recipient of a response, or in the case of one-way communication, between the actual moment of a signal?s broadcast and the time it is received at its destination. Compared to ground-based communication, all geostationary satellite communications experience high latency due to the signal; having to travel 35,786 km (22,236 mi) to a satellite in geostationary orbit and back to Earth again. A geostationary orbit, or ?Geostationary Earth Orbit? (?GEO?), is a circular orbit 35,786 km (22,236 mi) above the Earth?s equator and following the direction of the Earth?s rotation.

Even at the speed of light in vacuum (about 300,000 km/s or 186,000 miles per second), usually denoted by ?c,? a universal physical constant important in many areas of physics, this delay can be significant. If all other signaling delays could be eliminated, it still takes a radio signal about 250 milliseconds (ms), or about a quarter of a second, to travel to the satellite and back to the ground. For an internet packet, that delay is doubled before a reply is received that is the theoretical minimum. 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 ms latency for the total round-trip time (RTT) back to the user. This is much more than most dial-up users experience at typically 150-200 ms total latency, and two orders of magnitude higher than the typical 15-40 ms latency experienced by users of other high-speed internet services, such as: cable Internet access (often shortened to ?cable Internet? or simply ?cable?), which in telecommunications, is a form of broadband Internet access that uses the cable television infrastructure; or very-high-bitrate digital subscriber line (?VDSL? or ?VHDSL?), a digital subscriber line (DSL) technology providing faster data transmission over a single flat untwisted or twisted pair of copper wires (up to 52 Mbit/s downstream and 16 Mbit/s upstream), and on coaxial cable (up to 85 Mbit/s down- and -upstream) using the frequency band from 25 kHz to 12 MHz.

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Source: http://broadband-internet.ezinemark.com/signal-latency-a-satellite-internet-limitation-7d379bb88815.html

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