4 ms·

> 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

by 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").
  - zacmps 2y ago
    Correct
  - dghughes 2y ago
    I've read sharks see the cables as potential (ha!) prey due to slight EMF leakage. They chew on them damaging them. Not the fiber optic ones of course.
    - lxgr 2y ago
      All trans-oceanic cables carry an electric current in addition to light in fiber(s). Electricity is what powers the optical amplifiers of which there needs to be one every hundred or so kilometers. For short-ish cables (a couple hundred kilometers), driving the amplifiers via light (interestingly this can be done from both the data-sending and receiving end!) is possible, but not for trans-oceanic distances.
- staplung 2y ago
  Okay, I did a little more digging and it seems you're right eszed! Even undersea cables can increase their bandwidth, at least in some cases; seems to be dependent on some modulation factors that I don't fully understand. If I'm reading this right, BPSK - used on the longest transpacific cables - can't really be upgraded to have higher bandwidth but QPSK and other modulation schemes used for shorter distances can be (?).
  - lxgr 2y ago
    BPSK and QPSK are modulation schemes, but the optical amplifiers used don't demodulate and re-modulate at all, so the modulation used is irrelevant.
    - RoderickBeck 2y ago
      Correct. Modulation is encoding the bits in different aspects of the light wave. The better the modulation scheme, the more expensive is the division multiplexing equipment.
- frankjr 2y ago
  > undersea fiber-optic cables is that they need amplifiers every N kilometers Huh, I had no idea it needs to be done so frequently. > These days optical cable repeaters are photon amplifiers that operate at full gain at the bottom of the ocean for an anticipated service life of 25 years. > Repeaters are a significant cost component of the total cable cost, and there is a compromise between a ‘close’ spacing of repeaters, every 60km or so, or stretching the inter-repeater distance to 100km and making significant savings in the number of repeaters in the system. On balance it is the case that the more you are prepared to spend on the cable system the higher the cable carrying capacity. https://blog.apnic.net/2020/02/12/at-the-bottom-of-the-sea-a-short-history-of-submarine-cables/ https://blog.apnic.net/2020/02/12/at-the-bottom-of-the-sea-a... https://www.rp-photonics.com/propagation_losses.html https://www.rp-photonics.com/propagation_losses.html https://www.rp-photonics.com/fiber_amplifiers.html https://www.rp-photonics.com/fiber_amplifiers.html
- RoderickBeck 2y ago
  Not really. I know of no cases where optical amplifiers posed a barrier to upgrading. Ciena and Infinera have been able to upgrade cable capacity by several X. Optical amplifiers simply boost the signal. A photo is absorbed and then re-emitted with more power, but the same frequency and phase. There is no optical/electrical/optical conversion.
flakes 2y ago
When I was in school, I interned at a company that specializes in communication systems used to send data over these submarine cables. There is a huge market in terminal stations that send and receive over these cables. The terminal stations that communicate over the lines cost in the 50-100 million dollar range, but the cables themselves can cost upwards of a billion. Being able to maximize the efficiency of existing cables is a necessity. A large factor for the efficiency, is how “thin” you can make channels in the cable via frequency of the light. Multiple signals can be sent over a single fiber line if they use different frequencies. One system I was working on at the time was constructing 88 channels at 100gbs for a total throughput of 8.8tbs. Another very interesting aspect, is that service providers might share a lease of the same underwater cable, not actually owning the cable themselves. The companies enter an agreement on the frequency ranges assigned to them. Any mess ups in settings can cause disruption in your neighbor on the cable, resulting in millions of dollars of fines.
- positr0n 2y ago
  https://news.ycombinator.com/item?id=42048358 https://news.ycombinator.com/item?id=42048358 The levels of buying internet service simplified: 1. Pay for best effort traffic level. E.g. A residential user paying for 1gbps service 2. Pay for guaranteed traffic level. E.g. a business paying for guaranteed 10gbps. Often this maps to paying for a dedicated frequency on a cable, but that's hidden from you, you are just provided an Ethernet port or two. 3. Pay for a dedicated frequency on a cable. Also called "lease a wave". As you noted this is the most common way to go undersea. But it's common over terrestrial cables too. In this case the purchaser is often responsible for their own optical networking equipment, and the service provider muxes together all their customers. Sounds like you know more about this than me. The service provider's equipment doesn't have protection if your neighbor is accidentally stepping on your frequency range? 4. Pay for an entire cable. Also called leasing dark fiber. It's 100% your responsibility to "light" it. To make it worth it you're usually using optical networking equipment to mux together several different waves, just like the above scenario undersea, just all different waves belong to you. Commonly used by big tech companies and ISPs to connect their datacenters and points if presences in big cities. Lots of times the company you lease the cable from is also your contractor to repair cuts and maintain the amplifiers every ~50km.

by eszed 2y ago

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").
- zacmps 2y ago
  Correct
- dghughes 2y ago
  I've read sharks see the cables as potential (ha!) prey due to slight EMF leakage. They chew on them damaging them. Not the fiber optic ones of course.
  - lxgr 2y ago
    All trans-oceanic cables carry an electric current in addition to light in fiber(s). Electricity is what powers the optical amplifiers of which there needs to be one every hundred or so kilometers. For short-ish cables (a couple hundred kilometers), driving the amplifiers via light (interestingly this can be done from both the data-sending and receiving end!) is possible, but not for trans-oceanic distances.
staplung 2y ago
Okay, I did a little more digging and it seems you're right eszed! Even undersea cables can increase their bandwidth, at least in some cases; seems to be dependent on some modulation factors that I don't fully understand. If I'm reading this right, BPSK - used on the longest transpacific cables - can't really be upgraded to have higher bandwidth but QPSK and other modulation schemes used for shorter distances can be (?).
- lxgr 2y ago
  BPSK and QPSK are modulation schemes, but the optical amplifiers used don't demodulate and re-modulate at all, so the modulation used is irrelevant.
  - RoderickBeck 2y ago
    Correct. Modulation is encoding the bits in different aspects of the light wave. The better the modulation scheme, the more expensive is the division multiplexing equipment.
frankjr 2y ago
> undersea fiber-optic cables is that they need amplifiers every N kilometers Huh, I had no idea it needs to be done so frequently. > These days optical cable repeaters are photon amplifiers that operate at full gain at the bottom of the ocean for an anticipated service life of 25 years. > Repeaters are a significant cost component of the total cable cost, and there is a compromise between a ‘close’ spacing of repeaters, every 60km or so, or stretching the inter-repeater distance to 100km and making significant savings in the number of repeaters in the system. On balance it is the case that the more you are prepared to spend on the cable system the higher the cable carrying capacity. https://blog.apnic.net/2020/02/12/at-the-bottom-of-the-sea-a-short-history-of-submarine-cables/ https://blog.apnic.net/2020/02/12/at-the-bottom-of-the-sea-a... https://www.rp-photonics.com/propagation_losses.html https://www.rp-photonics.com/propagation_losses.html https://www.rp-photonics.com/fiber_amplifiers.html https://www.rp-photonics.com/fiber_amplifiers.html
RoderickBeck 2y ago
Not really. I know of no cases where optical amplifiers posed a barrier to upgrading. Ciena and Infinera have been able to upgrade cable capacity by several X. Optical amplifiers simply boost the signal. A photo is absorbed and then re-emitted with more power, but the same frequency and phase. There is no optical/electrical/optical conversion.

flakes 2y ago

When I was in school, I interned at a company that specializes in communication systems used to send data over these submarine cables. There is a huge market in terminal stations that send and receive over these cables. The terminal stations that communicate over the lines cost in the 50-100 million dollar range, but the cables themselves can cost upwards of a billion. Being able to maximize the efficiency of existing cables is a necessity. A large factor for the efficiency, is how “thin” you can make channels in the cable via frequency of the light. Multiple signals can be sent over a single fiber line if they use different frequencies. One system I was working on at the time was constructing 88 channels at 100gbs for a total throughput of 8.8tbs. Another very interesting aspect, is that service providers might share a lease of the same underwater cable, not actually owning the cable themselves. The companies enter an agreement on the frequency ranges assigned to them. Any mess ups in settings can cause disruption in your neighbor on the cable, resulting in millions of dollars of fines.

positr0n 2y ago
https://news.ycombinator.com/item?id=42048358 https://news.ycombinator.com/item?id=42048358 The levels of buying internet service simplified: 1. Pay for best effort traffic level. E.g. A residential user paying for 1gbps service 2. Pay for guaranteed traffic level. E.g. a business paying for guaranteed 10gbps. Often this maps to paying for a dedicated frequency on a cable, but that's hidden from you, you are just provided an Ethernet port or two. 3. Pay for a dedicated frequency on a cable. Also called "lease a wave". As you noted this is the most common way to go undersea. But it's common over terrestrial cables too. In this case the purchaser is often responsible for their own optical networking equipment, and the service provider muxes together all their customers. Sounds like you know more about this than me. The service provider's equipment doesn't have protection if your neighbor is accidentally stepping on your frequency range? 4. Pay for an entire cable. Also called leasing dark fiber. It's 100% your responsibility to "light" it. To make it worth it you're usually using optical networking equipment to mux together several different waves, just like the above scenario undersea, just all different waves belong to you. Commonly used by big tech companies and ISPs to connect their datacenters and points if presences in big cities. Lots of times the company you lease the cable from is also your contractor to repair cuts and maintain the amplifiers every ~50km.