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> So do we sometimes lay cables on top of other cables down there? I don't know exactly how often this has occurred but I'd guess it's relatively rare. The com

> So do we sometimes lay cables on top of other cables down there? I don't know exactly how often this has occurred but I'd guess it's relatively rare. The companies that operate in this space are very specialized and sophisticated. The locations of pretty much every cable laid in the last half century is very precisely tracked and one of the first things that has to happen when preparing a new cable route is to undertake a high resolution side-scan sonar survey of all or part of the planned route. In shallower water the cables are typically buried under several meters of the seabed. > What governments do you have to go to to get approval to do this? Could I just run a string across the Atlantic Ocean? At the very least you'll need to have landing agreements with the countries at the various endpoints. In international waters I believe there are some laws that apply but I gather that it's more about liability. You'd have a lot of difficulty running a string across the Atlantic. Controlling the amount of slack on a cable that's being played out is incredibly finicky work. Keep in mind that the point where your hypothetical string is touching down on the sea bed might be several miles behind where you are and that your ship is going to be bobbing around on the surface and you get an idea. > If we do lay cables on top of other cables how high do they get stacked? Are there challenges to bring the lower cables back up? Does that happen? Or do we just keep them down there forever basically and upgrade the hardware at the terminal? Cables are routinely brought up for repair or disposal. The ships that do this are called Agreement ships. In 1866 the second-ever transatlantic cable was grappled up to the surface and repaired (it snapped while laying it the previous year). Modern cables are fiberoptic and do not increase their bandwidth once laid.

toast0 2y ago
> The locations of pretty much every cable laid in the last half century is very precisely tracked and one of the first things that has to happen when preparing a new cable route is to undertake a high resolution side-scan sonar survey of all or part of the planned route. When the cables aren't well buried, they can migrate. No link, but earlier today I saw a description of a repair that was significantly delayed because the cable ends were 15 km away from where they were expected to be. That said, I think there's a lot of area on the sea, and not a lot of cables, so chances of overlapping are low; especially if a survey is done of the new route immediately before. Although if they're buried, maybe you can't see them so well. And a little overlap here and there probably isn't a big deal, because most of the time cables are brought up, it's because they were severed, so likely it doesn't disturb the other cable too much on its way up.
- lxgr 2y ago
  Overlapping is guaranteed in at least every case where a new cable has a more southern/western terminal on one but a more northern/eastern terminal on the other continent as an existing one. No idea if specific care is taken to avoid that, or if it's even a problem, but I could imagine so for cables that are buried in the seabed – the act of burying the new one could damage the existing one. But cables are only buried in shallow waters, is my understanding (where there's high risk of an anchor destroying them), so as long as the point of overlap or intersection is in deep seas, I'd imagine it to not be a problem.
  - dguest 2y ago
    Yeah it's a 2d geometry, of course some of the cables will cross. The other reason that overlapping would be an issue is if they need to pull up a section to repair it and it's directly under another cable. But the ocean is really damn big and there are only O(100s) of submarine cables. In both the burying in shallow water case, and the deep water maintenance case, I'm guessing the chances of two cables being in the same place is very very small.
- RoderickBeck 2y ago
  I think that cable was SWM5. It ended up 15 kilometers from the original burial trench. This is why deep burial is recommended, but adds expense.
eszed 2y ago
> Modern cables are fiberoptic and do not increase their bandwidth once laid. No kind of expert at all, but I understood that better control over / perception of narrower bandwidths of light have allowed fiber-optic cables to improve their data throughput immensely. Is that incorrect? Or are you using a narrower, technical definition of "bandwidth" that I've not understood?
- staplung 2y ago
  I'm no expert either but a complicating factor for undersea fiber-optic cables is that they need amplifiers every N kilometers. So even if the cable itself could theoretically support more bandwidth, the amplifiers might not. The amplifiers contain lasers of their own that fire at very specific wavelengths.
  - lucasban 2y ago
    I never thought about it, but I’m assuming that means the cables also carry enough electricity to power the amplifiers?
    - staplung 2y ago
      Yeah, the amplifiers need 10,000 volts. The way the cable is constructed is to have the fiber pairs inside a copper tube (there's some other stuff in between too). The voltage is carried by the tube. The ocean itself serves as the ground.
      - dfox 2y ago
        In general the power to the amplifiers is series connected and the ocean does not come into the question at all. If it did you would have huge issues with corrosion even ignoring the effects on the ocean itself. So, along the cable there is a wire that carries small DC current that goes between the amplifiers, each amplifier places zener diode along this wire and gets its power from it. At each landing station there is a current source (that is capable of developing significant open-circuit voltage) that powers this (this scheme is the reason why the cables are laid not only in loops, but in "loops-of-loops").
ay 2y ago
With DWDM one can increase the useful bandwidth of the cable; some useful links from a recent presentation that I had handy: https://m.youtube.com/watch?v=VKpAIx0zG-U https://m.youtube.com/watch?v=VKpAIx0zG-U https://nlnog.net/static/nlnogday2024/NLNOG2024-02-Yurii_Polovyi_-_A_Brief_history_of_DWDM.pdf https://nlnog.net/static/nlnogday2024/NLNOG2024-02-Yurii_Pol...
lxgr 2y ago
> Modern cables are fiberoptic and do not increase their bandwidth once laid. That's not true: The amplifiers they use work at the analog (and in fact even optical, i.e. without conversion to electric and back) level, and it's possible to upgrade capacity by only modifying the endpoints, not the entire cable.
- dietr1ch 2y ago
  Well, the usable capacity of the cable increases, but the cable itself has been doing it's job perfectly all the time :P I thought that endpoint upgrading of submarine cables was a sort of well known thing (at least amongst people that are aware their data goes and partly becomes a bunch of photons under the ocean, which I guess may be a lot of people here)
  - ta1243 2y ago
    Case in point, SEA-ME-WE-3 launched with a capacity of 20gbit back in 2000. Today it's been upgraded to 4600 gbit, a 200 fold increase.
  - RoderickBeck 2y ago
    The throughput can be dramatically increased by upgrading the DWDM kit. The optical amplifiers in the water are technologically agnostic. The fibre can be a gating factor. For a while fibre with chromatic dispersion compensation was used and that actually limits the ability to upgrade the cable using modern coherent optics. - The author.

toast0 2y ago

> The locations of pretty much every cable laid in the last half century is very precisely tracked and one of the first things that has to happen when preparing a new cable route is to undertake a high resolution side-scan sonar survey of all or part of the planned route. When the cables aren't well buried, they can migrate. No link, but earlier today I saw a description of a repair that was significantly delayed because the cable ends were 15 km away from where they were expected to be. That said, I think there's a lot of area on the sea, and not a lot of cables, so chances of overlapping are low; especially if a survey is done of the new route immediately before. Although if they're buried, maybe you can't see them so well. And a little overlap here and there probably isn't a big deal, because most of the time cables are brought up, it's because they were severed, so likely it doesn't disturb the other cable too much on its way up.

lxgr 2y ago
Overlapping is guaranteed in at least every case where a new cable has a more southern/western terminal on one but a more northern/eastern terminal on the other continent as an existing one. No idea if specific care is taken to avoid that, or if it's even a problem, but I could imagine so for cables that are buried in the seabed – the act of burying the new one could damage the existing one. But cables are only buried in shallow waters, is my understanding (where there's high risk of an anchor destroying them), so as long as the point of overlap or intersection is in deep seas, I'd imagine it to not be a problem.
- dguest 2y ago
  Yeah it's a 2d geometry, of course some of the cables will cross. The other reason that overlapping would be an issue is if they need to pull up a section to repair it and it's directly under another cable. But the ocean is really damn big and there are only O(100s) of submarine cables. In both the burying in shallow water case, and the deep water maintenance case, I'm guessing the chances of two cables being in the same place is very very small.
RoderickBeck 2y ago
I think that cable was SWM5. It ended up 15 kilometers from the original burial trench. This is why deep burial is recommended, but adds expense.

eszed 2y ago

> Modern cables are fiberoptic and do not increase their bandwidth once laid. No kind of expert at all, but I understood that better control over / perception of narrower bandwidths of light have allowed fiber-optic cables to improve their data throughput immensely. Is that incorrect? Or are you using a narrower, technical definition of "bandwidth" that I've not understood?

staplung 2y ago
I'm no expert either but a complicating factor for undersea fiber-optic cables is that they need amplifiers every N kilometers. So even if the cable itself could theoretically support more bandwidth, the amplifiers might not. The amplifiers contain lasers of their own that fire at very specific wavelengths.
- lucasban 2y ago
  I never thought about it, but I’m assuming that means the cables also carry enough electricity to power the amplifiers?
  - staplung 2y ago
    Yeah, the amplifiers need 10,000 volts. The way the cable is constructed is to have the fiber pairs inside a copper tube (there's some other stuff in between too). The voltage is carried by the tube. The ocean itself serves as the ground.
    - dfox 2y ago
      In general the power to the amplifiers is series connected and the ocean does not come into the question at all. If it did you would have huge issues with corrosion even ignoring the effects on the ocean itself. So, along the cable there is a wire that carries small DC current that goes between the amplifiers, each amplifier places zener diode along this wire and gets its power from it. At each landing station there is a current source (that is capable of developing significant open-circuit voltage) that powers this (this scheme is the reason why the cables are laid not only in loops, but in "loops-of-loops").

ay 2y ago

With DWDM one can increase the useful bandwidth of the cable; some useful links from a recent presentation that I had handy: https://m.youtube.com/watch?v=VKpAIx0zG-U https://m.youtube.com/watch?v=VKpAIx0zG-U https://nlnog.net/static/nlnogday2024/NLNOG2024-02-Yurii_Polovyi_-_A_Brief_history_of_DWDM.pdf https://nlnog.net/static/nlnogday2024/NLNOG2024-02-Yurii_Pol...

lxgr 2y ago

> Modern cables are fiberoptic and do not increase their bandwidth once laid. That's not true: The amplifiers they use work at the analog (and in fact even optical, i.e. without conversion to electric and back) level, and it's possible to upgrade capacity by only modifying the endpoints, not the entire cable.

dietr1ch 2y ago
Well, the usable capacity of the cable increases, but the cable itself has been doing it's job perfectly all the time :P I thought that endpoint upgrading of submarine cables was a sort of well known thing (at least amongst people that are aware their data goes and partly becomes a bunch of photons under the ocean, which I guess may be a lot of people here)
- ta1243 2y ago
  Case in point, SEA-ME-WE-3 launched with a capacity of 20gbit back in 2000. Today it's been upgraded to 4600 gbit, a 200 fold increase.
- RoderickBeck 2y ago
  The throughput can be dramatically increased by upgrading the DWDM kit. The optical amplifiers in the water are technologically agnostic. The fibre can be a gating factor. For a while fibre with chromatic dispersion compensation was used and that actually limits the ability to upgrade the cable using modern coherent optics. - The author.