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On a larger scale, the Meta Quest 2 uses a USB cable to plug into the computer so you can play VR games on your PC. The max length of the cable is something lik

On a larger scale, the Meta Quest 2 uses a USB cable to plug into the computer so you can play VR games on your PC. The max length of the cable is something like 3 feet over copper. The link cable they sell switches from electric signals over copper to light over fiber, and then back to copper to get around the length limitations. Not really the same thing but still cool!

hnuser123456 4y ago
Any decent quality standard copper USB-C cable works fine, typically 15ft
- tragictrash 4y ago
  There's multiple data rates that it can run at, the highest has a reduced length over copper
nwiswell 4y ago
It's interesting that they did that. One of the main reasons why you only see fiber optics in enterprise applications is that if you bend the cables too much, they're ruined. SFP+ hardware is cheaper and has lower latency than 10GBASE-T hardware, so in a vacuum it would be the obvious choice for everything. I'm not sure if they just decided the conventional wisdom that consumers would ruin the cable was wrong, or if they figured out how to make them idiot-proof.
- lordlimecat 4y ago
  Sfp isn't copper vs fiber. It's just the standard for a modular plug on network hardware. They have 25gbe twinax SFP28s that, as far as I'm aware, have essentially identical performance specs to using optical SFP28s with fiber. The fiber is thinner and can go further, but it also is more fragile and limited on bends. Latency is almost entirely driven by the switch and the NIC. Photons in fiber do not move meaningfully faster than signals in copper, and speed of light in short datacenters runs is not the limiting factor In latency. Any meaningful processing will happen in electronics and converting from copper to fiber introduces more latency. There's a good paper on it here: https://www.commscope.com/globalassets/digizuite/2799-latency-in-optical-fiber-systems-wp-111432-en.pdf?r=1 https://www.commscope.com/globalassets/digizuite/2799-latenc... Tldr coax actually is faster (0.77c) than optical fiber (0.67c).
  - nwiswell 4y ago
    > Photons in fiber do not move meaningfully faster than signals in copper, and speed of light in short datacenters runs is not the limiting factor In latency. Any meaningful processing will happen in electronics and converting from copper to fiber introduces more latency. My understanding is that it has nothing to do with the speed of light for short-run cables. 10GBase-T uses block encoding that adds a couple microseconds of latency (which dwarfs the impact of the speed of light at short distances) and fiber (including SFP+) doesn't need to. Coax/twinax may not need the encoding schemes that twisted pair does, I'm not sure.
agentwiggles 4y ago
My current gig has a similar problem, with a piece of hardware that operates over USB. Cable lengths over 6m or so introduce sufficient voltage and current drop to cause intermittent issues with the sensor (which are really tough to troubleshoot if you don't already know about this). The solution has been to use fiber optic hubs with the same behavior you describe - copper cables on either end to connect the hardware to the computing unit and a long run of fiber in the middle to make up the required length. Pretty cool stuff!
- tragictrash 4y ago
  It's probably not voltage drop that's making your device operate incorrectly. It's most likely the added capacitance and or inductance of the wires skewing the high frequency data signal out of spec. Entirely possible it's voltage drop, I don't know the exact hardware, but at 6 meters, it's probably signal rather than power.
sitharus 4y ago
Since that cable is USB-C only, and I don't have USB-C ports on my gaming PC, I have a 5m (~16ft) USB-A to C cable. Pure copper all the way, just much heavier than a regular weight USB cable. I have no issues with data rate or packet loss at all.
parineum 4y ago
I have a 30m HDMI run that I bought several cables that were certified for HDMI 2.0b but all of them were pretty unreliable at that length. After returning a bunch I ended up buying a 50m (that's the shortest they had that would work) Optical HDMI cable and it's been smooth sailing since.

hnuser123456 4y ago

Any decent quality standard copper USB-C cable works fine, typically 15ft

tragictrash 4y ago
There's multiple data rates that it can run at, the highest has a reduced length over copper

nwiswell 4y ago

It's interesting that they did that. One of the main reasons why you only see fiber optics in enterprise applications is that if you bend the cables too much, they're ruined. SFP+ hardware is cheaper and has lower latency than 10GBASE-T hardware, so in a vacuum it would be the obvious choice for everything. I'm not sure if they just decided the conventional wisdom that consumers would ruin the cable was wrong, or if they figured out how to make them idiot-proof.

lordlimecat 4y ago
Sfp isn't copper vs fiber. It's just the standard for a modular plug on network hardware. They have 25gbe twinax SFP28s that, as far as I'm aware, have essentially identical performance specs to using optical SFP28s with fiber. The fiber is thinner and can go further, but it also is more fragile and limited on bends. Latency is almost entirely driven by the switch and the NIC. Photons in fiber do not move meaningfully faster than signals in copper, and speed of light in short datacenters runs is not the limiting factor In latency. Any meaningful processing will happen in electronics and converting from copper to fiber introduces more latency. There's a good paper on it here: https://www.commscope.com/globalassets/digizuite/2799-latency-in-optical-fiber-systems-wp-111432-en.pdf?r=1 https://www.commscope.com/globalassets/digizuite/2799-latenc... Tldr coax actually is faster (0.77c) than optical fiber (0.67c).
- nwiswell 4y ago
  > Photons in fiber do not move meaningfully faster than signals in copper, and speed of light in short datacenters runs is not the limiting factor In latency. Any meaningful processing will happen in electronics and converting from copper to fiber introduces more latency. My understanding is that it has nothing to do with the speed of light for short-run cables. 10GBase-T uses block encoding that adds a couple microseconds of latency (which dwarfs the impact of the speed of light at short distances) and fiber (including SFP+) doesn't need to. Coax/twinax may not need the encoding schemes that twisted pair does, I'm not sure.

agentwiggles 4y ago

My current gig has a similar problem, with a piece of hardware that operates over USB. Cable lengths over 6m or so introduce sufficient voltage and current drop to cause intermittent issues with the sensor (which are really tough to troubleshoot if you don't already know about this). The solution has been to use fiber optic hubs with the same behavior you describe - copper cables on either end to connect the hardware to the computing unit and a long run of fiber in the middle to make up the required length. Pretty cool stuff!

tragictrash 4y ago
It's probably not voltage drop that's making your device operate incorrectly. It's most likely the added capacitance and or inductance of the wires skewing the high frequency data signal out of spec. Entirely possible it's voltage drop, I don't know the exact hardware, but at 6 meters, it's probably signal rather than power.

sitharus 4y ago

Since that cable is USB-C only, and I don't have USB-C ports on my gaming PC, I have a 5m (~16ft) USB-A to C cable. Pure copper all the way, just much heavier than a regular weight USB cable. I have no issues with data rate or packet loss at all.

parineum 4y ago

I have a 30m HDMI run that I bought several cables that were certified for HDMI 2.0b but all of them were pretty unreliable at that length. After returning a bunch I ended up buying a 50m (that's the shortest they had that would work) Optical HDMI cable and it's been smooth sailing since.