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May 4, 2024 18:53
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- Ignoarints
- Nov 26, 2010
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My boss thought my internet bill was low when I handed him the bill, so he told to upgrade my speed if I wanted.
Paying around the equivalent of $35 
I remember these days. It was in fact my only choice too
Welcome to the world of satellite communication. Most consumer satellite networks are in geostationary orbit because it allows a stationary dish rather than requiring expensive tracking and positioning equipment to constantly re-point the dish. Geostationary orbit for this planet is 22,236 miles above the equator. If you recall your high school physics class, the speed of light is 186,282 miles per second.
22236 miles / (186282 miles / second) = 0.1194 seconds or 119.4 milliseconds.
That's the one-way trip time from the moment the signal is emitted from the ground until it is received at the satellite or vice versa. Also, achieving this time requires being directly underneath the satellite. If you're anywhere else on the planet you're probably further away, adding more time.
Now let's think about a ping. For simplicity's sake let's say you're pinging something at the ISP's headend rather than actually going out over the internet, and we'll ignore any latency introduced in the modem, satellite, or headend equipment as it should be relatively minimal.
000 ms: Your computer sends the ping, the modem transmits it to the satellite.
120 ms: The satellite receives the message, forwards it to the headend.
240 ms: The headend receives the message, sends it to the target computer.
240 ms: The target computer receives the ping, replies.
240 ms: The headend transmits the reply up to the satellite.
360 ms: The satellite receives the message, forwards it back down to your modem.
480 ms: Your modem receives the reply and forwards it to your computer.
That's almost a half of a second delay, bare minimum, in absolutely ideal conditions. Being further from the equator adds a few milliseconds to each leg, as does being at a different latitiude. For example where I'm at in NE Ohio (41.1N, 81.7W) to the Exede satellite in the 115.1W orbital slot the extra distance would add another 9 milliseconds. It looks like most of their ground stations are in the western US, so picking the closest one to the bird in Tuscon, AZ (32N, 111W) there's 4 milliseconds there as well. That puts us at 506 milliseconds minimum theoretical round-trip time from an average US location without having even reached the internet.
This is why no one ever recommends satellite over terrestrial broadband services. It is an option of last resort for those who can't get useful service any other way. Real-time games are made effectively unplayable and any sort of live communication takes on a delay comparable to that of an old-school international telephone call (which of course used geostationary satellites).
A satellite service provider can of course operate at a lower altitude to reduce latency, as well as using orbits that cross over the targeted service area, but this introduces a number of problems including how to point the clients at the birds, relaying messages when the bird is in a spot that it can't see a ground station, and additional fuel requirements to maintain the proper orbit with greater drag from the slight bits of atmosphere out there. You also need a lot of equipment up there instead of just one. The Iridium satellite network uses this approach with 66 active satellites and a few spares. Obviously all this costs significantly more to operate than a single big satellite in GEO with a bunch of spot beams.
And I remember all this when I suffered on this. Very clearly. In fact, learning about those very satellites and then later finding out how low other satellites could be gave me a super strong perception of how large and small our planet is (combined with some live feed of the earth channel on dish network). All because of lovely satellite internet pings. It was so bad it opened up my mind.
Ignoarints fucked around with this message at 07:05 on Apr 23, 2014
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Apr 23, 2014 07:03
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in reality, I would see ~85 for each, upload usually higher. The best part was it was the only internet option for the whole building
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Mar 14, 2014 18:58
