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Comment by abainbridge | Hacker News Reader

Does anyone know if the paths shown for the transatlantic cables are anything like accurate? I would have expected them to follow "great circle" routes since they are the shortest. For example, the shortest path from Long Island to the Bristol Channel goes through Newfoundland and the southern tip of Ireland. There are several cables on the map with those end points but none of them are shown as taking that route. I guess this is poetic license that ignores the distortion of the map projection. Is there a map that shows the routes more accurately?

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https://kis-orca.eu/map/ is a very accurate map, but doesn't cover the whole world. You can compare the cables in and leaving Europe to decide whether you think https://www.submarinecablemap.com/ is particularly accurate or not.

Interesting. The westbound cables on that map all look like the are going too far South too. It would be interesting to know why.

Looking at the map of the Amitié cable, maybe they try to keep as much of the cable as possible in deep water. https://www.submarinenetworks.com/en/systems/trans-atlantic/...

The extra distance for NY/NJ-Bristol cables to cover is "just" ~400-500km (extra ~7%), plus if you look at ocean floor map [1] it seems they prefer not to put the cable in the relatively shallow waters of Newfoundland or Nova Scotia (maybe this decreases possibility of a damage by anchors, or they compensate a bit in length by going deeper, i.e. shorter circumference due to smaller radius).

The other possibility is that the direct path passes underwater mountainous region with quite variable depths in mid-Atlantic [1], so going up-down or follow the valleys anyway would increase the cable length. The right answer is likely a combination of all these to minimize cable cost, maintenance and latency.

[1] https://earth.google.com/web/@41.47661069,-40.80459324,-4414...

1901 telegraph submarine cables [1] were more straight for a similar route. Likely because it was essential to make them as short as possible going underwater, so most of them were going from Ireland to Newfoundland.

[1] https://upload.wikimedia.org/wikipedia/commons/a/a5/1901_Eas...

Ships anchors and trawlers are major risks for subsea cables. Deeper is thus better.

Underwater geography is also a major consideration. It's not just the going up and down, it's the risk of landslides, tectonic shifts, volcanoes, currents and icebergs scraping the ocean floor.

On top of that are geopolitics and enviromental concerns.

Why is Facebook involved in infrastructure like this?

Facebook is responsible for about 8% of all Internet traffic. They need subsea cables to connect their datacenters and to deliver traffic to end users.

Facebook operates a vast global network connecting its datacenters and points of presence (POPs). When you connect to Facebook from, say, Tokyo your HTTPS connection is terminated in a local point of presence (likely in Tokyo or somewhere in Japan) and from there the connection is forwarded on to a datacenter in the US or Europe. This forwarding happens over Facebook's privately operated network backbone, which needs to be substantial enough to handle billions of users' traffic (not to mention internal replication traffic and so on). Renting capacity from commercial providers is expensive so Facebook and the other big tech companies are interested in building their own infrastructure for this purpose.

Of course, it would be possible to have a user in Tokyo connect to Facebook's network somewhere closer to the DC but a) getting onto FB's high quality, low congestion network ASAP will perform yield much better performance than leaving the connection running over the internet where it's subject to congestion and long SSL connection round trips, b) terminating user sessions in POPs allows much finer control over which datacenter users are ultimately sent to. Without this FB would have to rely on DNS changes to steer traffic and they are slow to propagate and crude.

Interesting map. Astounding number of repeaters needed on a cable (you can show this in a map layer).

They must deliver some power with the cable to handle the repeaters? I wonder how much power it requires and if it's hard to ensure it doesn't break.

The cable landing stations provide DC power for the repeaters from both directions. The power requirements are substantial and use thousands of volts.

All the components of the subsea cable system are engineered with reliability in mind. None of the components are to require maintenance over the lifetime of the system. This means components are expected to operate 20 to 25 years at a minimum.

> The power requirements are substantial and use thousands of volts.

While 100% correct statement, the wording here could potentially lead someone to make an invalid assumption.

The core reason why it’s “thousands of volts” isn’t because a lot of power is needed specifically (although that is the case), it’s because of the nature of electrical conductors. Power loss over long distances is much more heavily influenced by current (current is squared in fact in the equation) rather than voltage. To say another way, you’ll have a lot less power loss with 50k volts at 100 amps than you would with 250V at 2,000A, despite both having comparable wattage (this is in part why high voltage power lines exist on land). Another reason is that electrical conductors (especially with copper, but also with aluminum and others) are heavy and the higher the amperage, the larger the conductor needs to be and thus the more weight.

A submarine cable can't just connect two end points by the great circle route. A cable route has to consider subsea geographics and geopolitics. This includes volcanoes and congress. Either one can be a big obstacle.

> Is there a map that shows the routes more accurately?

Maybe marine charts do, but also could be classified once they reach massive depths.

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