Forum

Marcus had a blog post on this not too long ago, but now I'm experiencing it first hand.

Wi-Fi in the Sky. Hey... that sounds kind of cool. Oh darn, the domain name www.wifiinthesky.com is taken.

Anyway, I'm on Southwest (by far the best airline in business). They are testing their (currently free) Wi-Fi Internet service. Here is my official report:

- You can tell that it works via satellite. Lag times can be from 1-4 seconds
- Ping times are about 700ms
- I did a speed test from www.speakeasy.net/speedtest. 4 Mbps down and 200 Kbps up.
- They are definitely filtering traffic, but that was to be expected. I can't use Skype (I wanted to use the chat feature). I'm trying to change the port but that doesn't seem to be working.

You won't be doing any Internet gaming with this latent of a connection, but having the Internet on an airplane... nice.

GT

P.S. I'm resisting the urge to fire up OmniPeek. I need one of those "you can't see my screen" overlays.

Oh... I just started watching the latest episode of Burn Notice on Hulu.com... warm fuzzy...


GT

Excellent information!!

BTW, you're a total nerd. Welcome to the best place on the web for wireless nerds. :D

Devinator

A few interesting points here. The satellite in use will probably be a geostationary satellite. This means that the satellite appears to be above the same position on the earth as viewed from an observer on the earth???¡é?¡é?????¡é???¡és surface. These satellites are about 22,300 miles above the surface of the earth. All geostationary satellites are positioned in space above the equator. Technically speaking there is actually no such thing as a TRUE geostationary satellite, and I have put some notes about this at the bottom of the page.

http://cimss.ssec.wisc.edu/sage/remote_sensing/lesson1/images/geo_orbit.jpg

Arthur C Clarke [ The science fiction writer who wrote ???¡é?¡é?????¡­?¡°2001 A Space Odyssey???¡é?¡é???????? ] originally came up with the concept of using the geostationary orbit, but was mocked by many at the time. Sadly he did not patent his ideas. Had he done so, he would literally have made Bill Gates look like a pauper.

So, why do we have so much delay when using a geosat ? Imagine that we were exactly underneath the satellite on the equator. We send a signal to the satellite vertically upwards. Remembering from our CWNA studies that RF signals travel at 3 X 10 to the power 8 m/s or 186,000 miles per second, we can work out the travel delay time.

Time = distance/velocity = 22,300 miles/186,000 miles per second.

Time = 0.120 seconds or 120 milliseconds.

Time to go up to the satellite and back down again = twice previous value = 2 x 120 ms = 240 ms.

As we move away from the spot on the equator [ called the sub-sat point ], the distance to the satellite [ called the slant range ] increases. If we wish someone to respond to us, they now have to send a signal from the ground back up to the satellite and back down again.

Total time = 2 x 240 ms = 480 ms, almost half a second or 0.5s

Have you ever pinged a site overseas and had a response that took over 500 ms ? There is a good chance that the link went over a satellite. In the US and overseas, most communications take place via cable [ mostly fiber optic ] whose lengths are much shorter than the distance to a satellite.

So where do the other times come into play to make up the 700 ms that Grant spoke of ? There are processing delays at the facilities that house the satellite equipment, then there are delays getting physically [ usually via cable ] to the particular website concerned. The satellite itself introduces a small delay as the signal is passed through devices called transponders on the satellite.

There are also non-geostationary satellites used for communications [ these guys move across the earth as viewed from an observer on the ground ]. These are much more difficult to use, as both the aircraft and satellite are moving relative to one another.

http://www.outfitterconnect.com/site/files/cm/Image/graphics/Coverage%20Map%20-%20Iridium.jpg

So why did I say there is no such thing as a truly geostationary satellite [ and will never be ] ? A geosat stays in orbit due to the balance of two main forces: a centrifugal force trying to pull the satellite away into space and a centripetal force [ due to the earths???¡é?¡é?????¡é???¡é gravity ] trying to pull it towards earth. Despite what we learned at school, the earth is not round. It is actually an oblate spheroid, meaning that it is ???¡é?¡é?????¡­?¡°squashed???¡é?¡é???????? at the North and South poles, like an American football. The diameter from pole to pole is different than that of the equator. A difference of only tens of miles, but this causes the satellite to drift. The earth is also not circular at the equator. It has two bulges. One just above where Sri Lanka is [ below India ] and another one out in the Pacific Ocean. If nothing was done, a satellite would eventually drift to one of these points. To prevent this, signals are sent from a control station to activate small rocket motors [ called thrusters ] to move the satellite back into place. When the fuel runs out, that is the end of the satellite???¡é?¡é?????¡é???¡és useful life in most cases. Solar pressure from tiny particles coming from the Sun cause a force on the satellite???¡é?¡é?????¡é???¡és body causing it to move. There are other factors as well such as the gravitational pull from the Sun and Moon. We should call them NEARLY geostationary satellites, but just geostationary is what we call them now.

http://www.weathernewengland.com/wp-content/uploads/2008/09/cam7.jpg


http://www.ctiinfo.com/SatControl/ComTrack/InclinedOrbitTutorial/satgeom5.htm

Dave

devinator Escribi?3:

Excellent information!!

BTW, you're a total nerd. Welcome to the best place on the web for wireless nerds. :D

Devinator

Wireless nerds make $ and get the chicks. Everyone knows this as fact.

GT

dave1234 Escribi?3:

A few interesting points here. The satellite in use will probably be a geostationary satellite. This means that the satellite appears to be above the same position on the earth as viewed from an observer on the earth???¡é?¡é?????¡é???¡és surface. These satellites are about 22,300 miles above the surface of the earth. All geostationary satellites are positioned in space above the equator. Technically speaking there is actually no such thing as a TRUE geostationary satellite, and I have put some notes about this at the bottom of the page.

http://cimss.ssec.wisc.edu/sage/remote_sensing/lesson1/images/geo_orbit.jpg

Arthur C Clarke [ The science fiction writer who wrote ???¡é?¡é?????¡­?¡°2001 A Space Odyssey???¡é?¡é???????? ] originally came up with the concept of using the geostationary orbit, but was mocked by many at the time. Sadly he did not patent his ideas. Had he done so, he would literally have made Bill Gates look like a pauper.

So, why do we have so much delay when using a geosat ? Imagine that we were exactly underneath the satellite on the equator. We send a signal to the satellite vertically upwards. Remembering from our CWNA studies that RF signals travel at 3 X 10 to the power 8 m/s or 186,000 miles per second, we can work out the travel delay time.

Time = distance/velocity = 22,300 miles/186,000 miles per second.

Time = 0.120 seconds or 120 milliseconds.

Time to go up to the satellite and back down again = twice previous value = 2 x 120 ms = 240 ms.

As we move away from the spot on the equator [ called the sub-sat point ], the distance to the satellite [ called the slant range ] increases. If we wish someone to respond to us, they now have to send a signal from the ground back up to the satellite and back down again.

Total time = 2 x 240 ms = 480 ms, almost half a second or 0.5s

Have you ever pinged a site overseas and had a response that took over 500 ms ? There is a good chance that the link went over a satellite. In the US and overseas, most communications take place via cable [ mostly fiber optic ] whose lengths are much shorter than the distance to a satellite.

So where do the other times come into play to make up the 700 ms that Grant spoke of ? There are processing delays at the facilities that house the satellite equipment, then there are delays getting physically [ usually via cable ] to the particular website concerned. The satellite itself introduces a small delay as the signal is passed through devices called transponders on the satellite.

There are also non-geostationary satellites used for communications [ these guys move across the earth as viewed from an observer on the ground ]. These are much more difficult to use, as both the aircraft and satellite are moving relative to one another.

http://www.outfitterconnect.com/site/files/cm/Image/graphics/Coverage%20Map%20-%20Iridium.jpg

So why did I say there is no such thing as a truly geostationary satellite [ and will never be ] ? A geosat stays in orbit due to the balance of two main forces: a centrifugal force trying to pull the satellite away into space and a centripetal force [ due to the earths???¡é?¡é?????¡é???¡é gravity ] trying to pull it towards earth. Despite what we learned at school, the earth is not round. It is actually an oblate spheroid, meaning that it is ???¡é?¡é?????¡­?¡°squashed???¡é?¡é???????? at the North and South poles, like an American football. The diameter from pole to pole is different than that of the equator. A difference of only tens of miles, but this causes the satellite to drift. The earth is also not circular at the equator. It has two bulges. One just above where Sri Lanka is [ below India ] and another one out in the Pacific Ocean. If nothing was done, a satellite would eventually drift to one of these points. To prevent this, signals are sent from a control station to activate small rocket motors [ called thrusters ] to move the satellite back into place. When the fuel runs out, that is the end of the satellite???¡é?¡é?????¡é???¡és useful life in most cases. Solar pressure from tiny particles coming from the Sun cause a force on the satellite???¡é?¡é?????¡é???¡és body causing it to move. There are other factors as well such as the gravitational pull from the Sun and Moon. We should call them NEARLY geostationary satellites, but just geostationary is what we call them now.

http://www.weathernewengland.com/wp-content/uploads/2008/09/cam7.jpg


http://www.ctiinfo.com/SatControl/ComTrack/InclinedOrbitTutorial/satgeom5.htm

Dave

Dave,

If you don't mind providing more detail next time, that would be great. :) Kidding... thanks a lot for the great information!

GT

Holy crap! This is a SMOKIN good post. I just learned a ton of stuff I didn't know. Thanks Dave!

GTHill Escribi?3:

devinator Escribi?3:

Excellent information!!

BTW, you're a total nerd. Welcome to the best place on the web for wireless nerds. :D

Devinator

Wireless nerds make $ and get the chicks. Everyone knows this as fact.

GT

Clearly it's the satellite nerds who make the big $ and get the... uhm... big chicks.