Post by europe-satellite.com on Dec 30th, 2012 at 11:20am
Signal latency.
For geostationary satellites, there is no way to eliminate latency.
Source, Wikipedia, for more info click here.
Latency is the delay between requesting data and the receipt 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.
Geostationary unsuitable for low-latency applications.
A (or geostationary Earth orbit/GEO) is a geosynchronous orbit directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers. Communications satellites and weather satellites are often given geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them, but can be pointed permanently at the position in the sky where they stay. Due to the constant 0° latitude and circularity of geostationary orbits, satellites in GEO differ in location by longitude only.
Compared to ground-based communication, all geostationary satellite communications experience high latency due to the signal having to travel (2x) 35,786 km (22,236 mi) to a satellite in geostationary orbit and back to Earth again. Even at the speed of light (about 300,000 km/s or 186,000 miles per second), this delay can be significant. If all other signalling 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. The absolute minimum total amount of delay is variable, due to the satellite staying in one place in the sky, while ground based users can be directly below with a roundtrip latency of 239.6 ms, or far to the side of the planet near the horizon with a roundtrip latency of 279.0 ms.
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 or VDSL.
For geostationary satellites, there is no way to eliminate latency, but the problem can be somewhat mitigated in Internet communications with TCP acceleration features that shorten the round trip time (RTT) per packet by splitting the feedback loop between the sender and the receiver. Such acceleration features are usually present in recent technology developments embedded in new satellite Internet services.
Satellite latency (Avanti Hylas-1).
ADSL latency (British Telecom).
For geostationary satellites, there is no way to eliminate latency.
Source, Wikipedia, for more info click here.
Latency is the delay between requesting data and the receipt 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.
Geostationary unsuitable for low-latency applications.
A (or geostationary Earth orbit/GEO) is a geosynchronous orbit directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers. Communications satellites and weather satellites are often given geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them, but can be pointed permanently at the position in the sky where they stay. Due to the constant 0° latitude and circularity of geostationary orbits, satellites in GEO differ in location by longitude only.
Compared to ground-based communication, all geostationary satellite communications experience high latency due to the signal having to travel (2x) 35,786 km (22,236 mi) to a satellite in geostationary orbit and back to Earth again. Even at the speed of light (about 300,000 km/s or 186,000 miles per second), this delay can be significant. If all other signalling 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. The absolute minimum total amount of delay is variable, due to the satellite staying in one place in the sky, while ground based users can be directly below with a roundtrip latency of 239.6 ms, or far to the side of the planet near the horizon with a roundtrip latency of 279.0 ms.
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 or VDSL.
For geostationary satellites, there is no way to eliminate latency, but the problem can be somewhat mitigated in Internet communications with TCP acceleration features that shorten the round trip time (RTT) per packet by splitting the feedback loop between the sender and the receiver. Such acceleration features are usually present in recent technology developments embedded in new satellite Internet services.
Satellite latency (Avanti Hylas-1).
ADSL latency (British Telecom).
