5 ms·

> USB-C hubs are not possible like you could do with USB 2 or 3 TIL. Why is this not possible?

Nextgrid 6y ago
You'd probably find a more authoritative source and better documentation by searching, but here's my understanding of it: USB-C can be used with alternate modes like DisplayPort or Thunderbolt, where the wires are no longer transmitting USB data but are used as a dumb pipe for the underlying protocol. If you get a hub it can choose to either operate in the following conditions (depending on its type and capabilities): * Upstream port is in USB mode, it can provide USB 2 and 3 to downstream ports, however the downstream device can no longer use DisplayPort or Thunderbolt. * Upstream port is divided into USB 3 lanes and DisplayPort lanes. The DisplayPort side can be mapped to a single downstream port, but there is less USB 3 bandwidth available to share across the remaining ports. Still no luck if a downstream device wants to use Thunderbolt. * Upstream port is Thunderbolt. Since TB is essentially PCI Express the hub could pass through some TB lanes to a single downstream port while having its own USB 3 controller to provide the USB side of things. Still no luck for DisplayPort downstream devices. This doesn't even address the issue that not all devices can do Thunderbolt (my 12-inch Macbook can't) and it becomes very hard to find a hub that will actually work and do what you want. It took quite a bit of research for me to understand the specs so I could find a solution to do both 4K 60Hz video and USB (2 only, not enough bandwidth for 3) on my MacBook with a single USB-C port. I won't even get into the bullshit naming conventions they use that they decided to apply retroactively. WTF is USB 3.1 Gen 1? Is the next one gonna be called USB 10 X Pro Max?
- cannam 6y ago
  Oh that's interesting. That might be an extra reason why devices are still preferentially coming with USB3 type A plugs on the other end - it's actually more flexible that way? I am in fact plugging both of my new USB-C devices into a USB3 hub, and had no idea I wouldn't have been able to do the same with USB-C cables and hub. (I assume you can still have a USB3 hub with type A sockets on it, plugged in to a USB-C port? - edit: oh, just noticed a sibling comment says this doesn't seem to exist either. Now that is very odd.)
  - jki275 6y ago
    Usb 3 hubs with a USB-C upstream certainly exist, all the docks out there are functionally that, and there are also dedicated hubs as well. Here’s the one i use: Anker USB C Hub, Aluminum USB C Adapter with 4 USB 3.0 Ports, for MacBook Pro 2018/2017, ChromeBook, XPS, Galaxy S9/S8, and More https://www.amazon.com/dp/B07DFYQXY7 https://www.amazon.com/dp/B07DFYQXY7
- meroje 6y ago
  But I don't need or care about all that, what I need is a hub just like we had all those years that gives usb3 connectivity in a c form factor to 5 devices or more. If I need more there are plenty docking stations available. edit: I also looked for a usb A hub with usb-c upstream, still no luck and stuck with a hub+power adapter and dinky otg a-to-c.
  - Nextgrid 6y ago
    As far as I know the spec doesn't allow it for some reason. I guess one reason could be the power side (which I haven't mentioned and I am not familiar with it)? Let's assume the hub requests 19V from the upstream port. Unless it has built-in, variable, per-port voltage regulation, it will not be able to respond to power requests from the downstream devices if they differ from what is coming from the upstream port. This isn't a problem when providing USB-A ports because you either request 5V from upstream and pass it through or request a higher voltage and have a single 5V regulator and pass its output to the downstream ports.
    - Kirby64 6y ago
      See, you could technically design something that does that. Per-port up to 100W charging it definitely possible. Basically you have a USB PD controller on every port with dynamic voltage control. This is all possible, it's just a HUGE pain in the ass (and costs a lot) to design that way. The problem is you essentially end up with potentially a giant, VERY expensive USB hub. And no one wants to spend $400 on a USB hub.
      - Nextgrid 6y ago
        Which is why USB-C is bad, nobody asked for a protocol where the benefits are marginal but the downside (one of many) is that a proper hub that replicates the behavior of previous generations now costs more, and since nobody would pay that much, economies of scale don't apply and thus it doesn't exist at all or is available as very niche specialized units (kinda like opto-isolated USB hubs which go for $200. You could also theoretically use 10Gbit Ethernet to transfer data from your phone but we don't go around putting SFP slots on phones because we don't want every single cable or charger to cost $100 and be more complex (thus more prone to failure) than needed.
- hahahahahka 6y ago
  USB-C. Universal Serial Bus, without the universal part.
Kirby64 6y ago
It's definitely possible, it's just a bit expensive. There's nothing in the USB-C spec that disallows you from doing this. Also if you're trying to do the thing where you have charging input but data output on one port, it gets complicated. That said, I see no reason why you couldn't design a basic USB-C USB2 or USB3 hub. Hell, it could have 5 ports with no defined 'input' port (just 5 USB C jacks), and you could have that work properly with some pain. If it has a captive USB-C cable and 4 USB-C outputs, that would be even easier to program. Again, it's just expensive. You need a lot of active circuitry to make it work.

You'd probably find a more authoritative source and better documentation by searching, but here's my understanding of it: USB-C can be used with alternate modes like DisplayPort or Thunderbolt, where the wires are no longer transmitting USB data but are used as a dumb pipe for the underlying protocol. If you get a hub it can choose to either operate in the following conditions (depending on its type and capabilities): * Upstream port is in USB mode, it can provide USB 2 and 3 to downstream ports, however the downstream device can no longer use DisplayPort or Thunderbolt. * Upstream port is divided into USB 3 lanes and DisplayPort lanes. The DisplayPort side can be mapped to a single downstream port, but there is less USB 3 bandwidth available to share across the remaining ports. Still no luck if a downstream device wants to use Thunderbolt. * Upstream port is Thunderbolt. Since TB is essentially PCI Express the hub could pass through some TB lanes to a single downstream port while having its own USB 3 controller to provide the USB side of things. Still no luck for DisplayPort downstream devices. This doesn't even address the issue that not all devices can do Thunderbolt (my 12-inch Macbook can't) and it becomes very hard to find a hub that will actually work and do what you want. It took quite a bit of research for me to understand the specs so I could find a solution to do both 4K 60Hz video and USB (2 only, not enough bandwidth for 3) on my MacBook with a single USB-C port. I won't even get into the bullshit naming conventions they use that they decided to apply retroactively. WTF is USB 3.1 Gen 1? Is the next one gonna be called USB 10 X Pro Max?

cannam 6y ago
Oh that's interesting. That might be an extra reason why devices are still preferentially coming with USB3 type A plugs on the other end - it's actually more flexible that way? I am in fact plugging both of my new USB-C devices into a USB3 hub, and had no idea I wouldn't have been able to do the same with USB-C cables and hub. (I assume you can still have a USB3 hub with type A sockets on it, plugged in to a USB-C port? - edit: oh, just noticed a sibling comment says this doesn't seem to exist either. Now that is very odd.)
- jki275 6y ago
  Usb 3 hubs with a USB-C upstream certainly exist, all the docks out there are functionally that, and there are also dedicated hubs as well. Here’s the one i use: Anker USB C Hub, Aluminum USB C Adapter with 4 USB 3.0 Ports, for MacBook Pro 2018/2017, ChromeBook, XPS, Galaxy S9/S8, and More https://www.amazon.com/dp/B07DFYQXY7 https://www.amazon.com/dp/B07DFYQXY7
meroje 6y ago
But I don't need or care about all that, what I need is a hub just like we had all those years that gives usb3 connectivity in a c form factor to 5 devices or more. If I need more there are plenty docking stations available. edit: I also looked for a usb A hub with usb-c upstream, still no luck and stuck with a hub+power adapter and dinky otg a-to-c.
- Nextgrid 6y ago
  As far as I know the spec doesn't allow it for some reason. I guess one reason could be the power side (which I haven't mentioned and I am not familiar with it)? Let's assume the hub requests 19V from the upstream port. Unless it has built-in, variable, per-port voltage regulation, it will not be able to respond to power requests from the downstream devices if they differ from what is coming from the upstream port. This isn't a problem when providing USB-A ports because you either request 5V from upstream and pass it through or request a higher voltage and have a single 5V regulator and pass its output to the downstream ports.
  - Kirby64 6y ago
    See, you could technically design something that does that. Per-port up to 100W charging it definitely possible. Basically you have a USB PD controller on every port with dynamic voltage control. This is all possible, it's just a HUGE pain in the ass (and costs a lot) to design that way. The problem is you essentially end up with potentially a giant, VERY expensive USB hub. And no one wants to spend $400 on a USB hub.
    - Nextgrid 6y ago
      Which is why USB-C is bad, nobody asked for a protocol where the benefits are marginal but the downside (one of many) is that a proper hub that replicates the behavior of previous generations now costs more, and since nobody would pay that much, economies of scale don't apply and thus it doesn't exist at all or is available as very niche specialized units (kinda like opto-isolated USB hubs which go for $200. You could also theoretically use 10Gbit Ethernet to transfer data from your phone but we don't go around putting SFP slots on phones because we don't want every single cable or charger to cost $100 and be more complex (thus more prone to failure) than needed.
hahahahahka 6y ago
USB-C. Universal Serial Bus, without the universal part.

Kirby64 6y ago

It's definitely possible, it's just a bit expensive. There's nothing in the USB-C spec that disallows you from doing this. Also if you're trying to do the thing where you have charging input but data output on one port, it gets complicated. That said, I see no reason why you couldn't design a basic USB-C USB2 or USB3 hub. Hell, it could have 5 ports with no defined 'input' port (just 5 USB C jacks), and you could have that work properly with some pain. If it has a captive USB-C cable and 4 USB-C outputs, that would be even easier to program. Again, it's just expensive. You need a lot of active circuitry to make it work.