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Comment by williamle8300 | Hacker News Reader

We have satellites that are pretty fast... what's the point of laying down physical submarine wires?

1. Satellites aren’t used because they can’t carry terabytes of data for less than a billion dollars per communication line.

2. The bandwidth available using a single fiber optic cable and a laser beam is much much greater than you can get from a single satellite radio channel. This is due to the higher frequency and shorter wavelength of light compared to microwaves. The higher the frequency, the greater the bandwidth.

3. An undersea cable is a bundle many fiber optic cables. Consider each fiber cable as a channel. You can have more channels, each with a higher capacity, than you can build radio channels into a satellite.

4. The uplinks and downlinks cost and putting the satellite in space is a huge huge ask and far more risky.

5. The delay for satellite communications would be around 255ms both uplink and downlink. For continuous traffic this not to a bad price to pay. But for burst traffic (like voice) you pay for the delay at each pause. The Rule of Thumb is 10MS per 1000 miles so Rule of Thumb to Europe on say TAT-8 would be about 75MS vs 510MS for satellite.

6. Finally, you can fix a broken cable. Once you launch the satellite you don’t get a chance to fix it if it gets broke.

re: #3, not exatcly, an underseas cable is actually relatively few strands compared to a terrestrial cable. Many older ones are only two strands. Modern ones 4 or 6 strands. It's the DWDM terminals on each end of the cable that enable fun things like 80 channels x 100 Gbps full duplex coherent QPSK per channel.

Latency, cost, and connection quality are usually the three big issues with satellite connections. For those reasons, they're usually only viable in remote areas with low populations (or otherwise low need for electronic communication); at some point, a physical connection ends up becoming necessary.

1) Satellites don't use fiber as a medium so have that against them 2) from point A to a satellite back to point B is generally going to be a pretty significant distance, as such, when combined when a comparatively slower medium you'll get increased latency, which is bad for interactive applications. 3) satellites can be susceptible to weather issues.

To clarify/correct here: satellites do not use a slower medium than fiber; satellite (and radio in general) and fiber communication both happen at the speed of light (since they both use light to communicate). If we had a space elevator, and someone were to string a fiber-optic cable along its length and ping something at the other end of it, it'd take just as long for that signal to reach the top of the elevator as it would to reach a satellite orbiting right next to it.

The "slowness" is due to the other factors you've described (the longer distances and the increased risk of environmental interference).

Thanks for clarifying/constructive correction!

I feel silly, because now I'm thinking about microwave internet and how fast it can be, especially paired with fiber on either end.

a geostationary satellite that weighs 6000 kilograms and costs $185 million to build and launch has less aggregate data throughput capacity than two strands of singlemode fiber in a cable with a diameter thinner than a pencil. And that is before you get into the fact that medium/long distance fiber these days is generally built with a cable that has a minimum of 144 strands in it, if not 288 or 864.

It's not even close when you're talking about 40 or 80-channel x 100 Gbps DWDM systems vs. satellite, whether it's geostationary or o3b.

Satellite is best used to reach very difficult to reach locations (example: Skardu Pakistan) or for maritime purposes.

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