5 ms·

So on the next versions of USB, the cable length will get shorter and shorter until the max gets to 5cm? While I get the technical reasoning about high frequen

So on the next versions of USB, the cable length will get shorter and shorter until the max gets to 5cm? While I get the technical reasoning about high frequency/attenuation etc that limits cable length as speeds go higher, there are obviously some practical limits to how short cables can be. How would that be solved, I don't know.

CoastalCoder 5y ago
Not my area of expertise, but maybe some (unrealistic) options include using fiber optics for the data lines, or adding more data lines.
- birktj 5y ago
  There already exists some fiber-optic USB cables that come in lengths >50m and with support for USB 3.1 so it doesn't seem like a very unrealistic option.
  - Chilinot 5y ago
    That sounds more like fiber optic adapters/converters that fit into usb-ports and talk usb, rather than USB-cables that can be 50+ meters.
    - jayd16 5y ago
      Seems like you can get 3m optical usb-c cables. Oculus sells an official "Full featured USB active optical cable. USB 3.2 Gen 1 Type-C" for tethered play. That's what the cheatsheet says so maybe that's part of the spec.
    - jsjohnst 5y ago
      I think GP is thinking of fiber optic Thunderbolt cables probably.
    - duskwuff 5y ago
      Some USB4 / Thunderbolt cables are like that, but with copper in the middle. The drivers on the device end wouldn't be able to maintain signal integrity over that size of cable, so there's a pair of transceivers in each end of the cable to convert the signal into a format that'll survive transmission.
    - Dylan16807 5y ago
      What's the difference between talking USB and being USB?
    - michaelt 5y ago
      https://www.amazon.com/FIBBR-Female-Active-Extension-Optical/dp/B07BW91RHZ https://www.amazon.com/FIBBR-Female-Active-Extension-Optical... provides USB-to-fibre-to-USB in a single cable, and a copper pair in parallel for power.
      - Aachen 5y ago
        $169+47 shipping for those curious Can't say it's not unique and cool, to be fair
  - Forgeties79 5y ago
    Redmere chips also proved HDMI can go very, very far with a little extra investment. I've run 4K signals hundreds of feet with them. We've seen this problem solved several times, I can't imagine it's physically impossible with USB-C.
- dual_dingo 5y ago
  I guess at some point optical will be the only way forward. Having more data lines in a serial bus is interesting, as the whole reasoning to go from parallel lines (e.g. Centronics, ATA/SCSI or ISA/PCI buses) to serial (SATA/SAS, PCIe, USB) was that coordinating multiple data lines got impossible due to physical limitations where e.g. minimal differences in cable lengths started to matter).
  - helpm33 5y ago
    Multiple serial busses, each with its own clocking and buffer, so that the combined data is extracted synchronously at the end. The crosstalk is still a problem but there are ways around that: different twist rates for different pairs for instance.
  - Dylan16807 5y ago
    > I guess at some point optical will be the only way forward. Maybe. Though Infiniband's currently at 100Gbps per lane on a 1.5 meter passive cable. And active cables can give you a moderate boost while still on copper.
    - paulmd 5y ago
      that's a giant QSFP+ cable (I think mine are at least 3/8") with tons of shielding and a terrible bend radius though. And my cables all have a "10 plug/unplug cycle lifespan" sticker on them - it undoubtedly will go for longer in practice but it's not designed for USB-style usage where you might plug and unplug your phone a dozen times a day as you charge it. Commercial design concerns are very different from consumer design concerns, basically. Phones would probably be easier if we had a 1/2" x 1/2" x 1.5" connector with a shielded connector body! ;)
moffkalast 5y ago
Keep the same speeds, add more wires.
- deleted 5y ago
  [deleted]
- Aachen 5y ago
  Printers hate this trick https://www.unm.edu/~tbeach/terms/images/oldportsBIG.jpg https://www.unm.edu/~tbeach/terms/images/oldportsBIG.jpg
zamadatix 5y ago
I'm confused what that section is supposed to represent. E.g. Apple has a 3 meter USB 4 3x2 (40 Gbps) cable but the "cable" value for that section is listed as 0.8m. The only hit I'm getting in the USB 4 spec for "0.8" is on page 59 referring to maximum receiver insertion loss in dB for a gen 3 connection including a 0.8m passive cable but that in itself isn't a hard limitation on cable length.

CoastalCoder 5y ago

Not my area of expertise, but maybe some (unrealistic) options include using fiber optics for the data lines, or adding more data lines.

birktj 5y ago
There already exists some fiber-optic USB cables that come in lengths >50m and with support for USB 3.1 so it doesn't seem like a very unrealistic option.
- Chilinot 5y ago
  That sounds more like fiber optic adapters/converters that fit into usb-ports and talk usb, rather than USB-cables that can be 50+ meters.
  - jayd16 5y ago
    Seems like you can get 3m optical usb-c cables. Oculus sells an official "Full featured USB active optical cable. USB 3.2 Gen 1 Type-C" for tethered play. That's what the cheatsheet says so maybe that's part of the spec.
  - jsjohnst 5y ago
    I think GP is thinking of fiber optic Thunderbolt cables probably.
  - duskwuff 5y ago
    Some USB4 / Thunderbolt cables are like that, but with copper in the middle. The drivers on the device end wouldn't be able to maintain signal integrity over that size of cable, so there's a pair of transceivers in each end of the cable to convert the signal into a format that'll survive transmission.
  - Dylan16807 5y ago
    What's the difference between talking USB and being USB?
  - michaelt 5y ago
    https://www.amazon.com/FIBBR-Female-Active-Extension-Optical/dp/B07BW91RHZ https://www.amazon.com/FIBBR-Female-Active-Extension-Optical... provides USB-to-fibre-to-USB in a single cable, and a copper pair in parallel for power.
    - Aachen 5y ago
      $169+47 shipping for those curious Can't say it's not unique and cool, to be fair
- Forgeties79 5y ago
  Redmere chips also proved HDMI can go very, very far with a little extra investment. I've run 4K signals hundreds of feet with them. We've seen this problem solved several times, I can't imagine it's physically impossible with USB-C.
dual_dingo 5y ago
I guess at some point optical will be the only way forward. Having more data lines in a serial bus is interesting, as the whole reasoning to go from parallel lines (e.g. Centronics, ATA/SCSI or ISA/PCI buses) to serial (SATA/SAS, PCIe, USB) was that coordinating multiple data lines got impossible due to physical limitations where e.g. minimal differences in cable lengths started to matter).
- helpm33 5y ago
  Multiple serial busses, each with its own clocking and buffer, so that the combined data is extracted synchronously at the end. The crosstalk is still a problem but there are ways around that: different twist rates for different pairs for instance.
- Dylan16807 5y ago
  > I guess at some point optical will be the only way forward. Maybe. Though Infiniband's currently at 100Gbps per lane on a 1.5 meter passive cable. And active cables can give you a moderate boost while still on copper.
  - paulmd 5y ago
    that's a giant QSFP+ cable (I think mine are at least 3/8") with tons of shielding and a terrible bend radius though. And my cables all have a "10 plug/unplug cycle lifespan" sticker on them - it undoubtedly will go for longer in practice but it's not designed for USB-style usage where you might plug and unplug your phone a dozen times a day as you charge it. Commercial design concerns are very different from consumer design concerns, basically. Phones would probably be easier if we had a 1/2" x 1/2" x 1.5" connector with a shielded connector body! ;)

moffkalast 5y ago

Keep the same speeds, add more wires.

deleted 5y ago
[deleted]
Aachen 5y ago
Printers hate this trick https://www.unm.edu/~tbeach/terms/images/oldportsBIG.jpg https://www.unm.edu/~tbeach/terms/images/oldportsBIG.jpg

zamadatix 5y ago

I'm confused what that section is supposed to represent. E.g. Apple has a 3 meter USB 4 3x2 (40 Gbps) cable but the "cable" value for that section is listed as 0.8m. The only hit I'm getting in the USB 4 spec for "0.8" is on page 59 referring to maximum receiver insertion loss in dB for a gen 3 connection including a 0.8m passive cable but that in itself isn't a hard limitation on cable length.