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Linux 5.5 Bringing Thunderbolt Lane Bonding, DP Tunneling Updates

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  • #11
    Originally posted by [email protected] View Post
    I thought that the firat thunderbolt veraion was actually planned to be transmitting trough a fiber optics cable.

    I would really like it if they could resurrect that idea for the next USB generation. The current cables are a mess. With optics, there would be a lot more bandwidth, and no cross-talk, so the ability to run thicker power cables. Cables would also be a lot less expensive. The connector? Heck, maybe Jack-like, or even Jack-compatible :P
    I guess you have no experience with optical. I do, both with Toslink setups (consumer optical S/PDIF audio) and multimode fiber for fast server-server interconnect inside a datacenter.
    Optical for consumer-grade equipment is a plain inferior to copper.

    -optical cables have very big issues with bending and are much stiffer than a copper-based system. Even plastic-based fiber (the more tolerant one) will break or degrade significantly if bent at angles most copper-based cabes are bent every day for years without problems. You can try doing this with fiber optic used for RGB christmas decorations or something, where you bend it enough it will create fractures that refract the light in the bent part, which is bad.

    -optical transceivers are significantly more complex and expensive than electronic ones with the same bandwith. Toslink (ancient "optical audio" standard) is not a good example, its bandwith sucks and it is monodirectional. If you want better bandwith you need more complex systems.

    -optical transceivers tend to require bigger connectors than electrical ones.

    -optical cables for practical high-bandwith use are not thinner than copper. Forget the christmas decoration mm-thin fiber optic, the actual cable is as thicc as a decent USB 3.0 cable, and monodirectional (so you need two)

    -optical connections are more susceptible to connector damage (on normal networking patch fiber you need to put a cap on the fiber head to avoid it getting bent or scratched, or you need to deal with this when designing the connector) and fiber need to be reasonably clean to work (which is not an issue for server environment, but you know full well how dirty can a USB cable get). Electrical contacts are much more rugged and are "self-cleaning" for most basic situations as the contacts physically scrape on each other when making contact.

    -"crosstalk" is mostly a non-issue as we are talking of digital signals over a short distance (another reason why Toslink is a kind of pointless exercise, the signal is S/PDIF so it is a digital system. Using it over a decent coaxial cable is perfectly fine and does not have any of the bs an optical system has), and even then you can just have twisted pairs if you want better range.

    - Jack-like, or even Jack-compatible connectors (ala Toslink) mean you are using bidirectional optic technology while more classic transceivers are monodirectional (the cable is the same, but you need two fiber cables instead of just one like with Toslink that is monodirectional). This is possible but more expensive (and much more expensive than copper-based solutions), it's available in enterprise networking since around a decade ago and called BiDi. I would not hold my breath for this to become commonplace either.

    -power transmission over optical is not practical at all, so you would still need dedicated copper power lines. And none stops you from using thicker lines just for the power in a copper-based cable too.
    Last edited by starshipeleven; 11-04-2019, 02:41 AM.