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On submarine optical cables with one trunk and several landing points, how does data that leaves one landing point be routed to a desired destination at another landing point? I have many hypotheses:
- The data is broadcasted to every other landing point.
- The data is always sent to a specific other landing point, as at the branching point only some fiber strands are branched from the trunk.
Which one of them is true, or are all of them wrong?

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  • I believe your second statement is close to the truth. However there can be variations on this depending on whether you separate individual strands, or separate individual lambdas within the strands and then either route them optically, or convert them back to electric and re-emit onto the cable branch optically. Oct 6 '17 at 21:05
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin
    Feb 19 '18 at 20:34
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As others have said, it goes from one point to another. Here are some explanations from manufacturers.

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The second point is closer to accurate. Each strand has two (and only two) terminations. It may be that a set of strands leaving a given departure point is broken up into two smaller sets that end up in two different landing points but, again, at the strand level there's a single source and destination.

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Afaict there are several layers.

First there are individual strands of fiber, usually in pairs one for each direction. Afaict the number of strands on long distance undersea cables is relatively small compared to terrestrial or short distance undersea cables due to the need for optical amplification. Depending on the design of the cable system only a subset of the strands may be brought ashore at each landing.

On top of that you have WDM. The strands are split up into wavelengths which may be routed differently at the landing sites (including being sent back under the sea).

And on top of that you have digital data communications which again give many options for routing data.

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