![]() TB3 can share "superspeed" data lanes with DisplayPort, splitting the 40 Gbps total bandwidth with it. If there's a file copy from one USB 3.x device to another on the same dock then the time, and therefore total average bandwidth, gets split. If the other devices don't have much to say then one device will get nearly all the bandwidth. Each time slice it has will be at the full data rate. All USB 3.x devices will then split time on the USB "superspeed" lines to the host. ![]() A USB 3.2 device with a USB-C jack will not be able to even plug in to such a dock, or if it does get plugged in then it will be a power only USB-C port and the host won't even know it's there. A DisplayPort display might use USB 2.0 for making video adjustments since DisplayPort is a unidirectional protocol.Ī USB-C hub that lacks support for USB4 or TB3 will have only USB-A ports for USB 3.x devices. There might be some impact if a device uses the USB 2.0 lane for negotiating the data on the "superspeed" lanes. A keyboard, mouse, or other USB 2.0 device is not likely to impact anything on the "superspeed" data lanes. This is because the USB 2.0 data path is for the most part independent from the "superspeed" data lanes. The USB 2.0 lanes on a USB-C dock will act like the USB 2.0 would on any USB 2.0 hub. ![]() With no defined means to support a downstream USB-C port on a dock there's not much to gain with using all four "superspeed" lanes for USB 3.x data. USB4 fixes this, and TB3 docks avoid this, by putting a separate USB controller in the dock. Another issue is that the USB 3.x spec did not define how a USB-C port on a USB-C dock would work except for providing power. For one this leaves no "superspeed" lanes for video. It's possible for a USB-C dock to use all four "superspeed" lanes for USB 3.x data but I have yet to see such a dock. This is because the HDMI alternate mode on USB-C requires use of all four "superspeed" lanes, leaving nothing for USB 3.x devices. There might be a HDMI port on the USB-C dock but it will use two "superspeed" lanes for DisplayPort video and convert that into HDMI internally. Reasons that can get complicated quickly.Ī USB 3.x dock will most likely use one pair of these "superspeed" lanes for USB 3.x data and the other pair for DisplayPort video. There are other alternate modes that a dock could use but I have not seen any and using any protocols other than those three don't make much sense for a number of reasons. USB-C has four "superspeed" data lanes which can be used for USB 3.x, DisplayPort, or TB3 data. That is unless I'm missing something important. The portions of the spec that differentiate USB4 from TB3 are all optional, an existing TB3 hub or dock does not have to change anything to meet the USB4 spec. There's USB4 docks now too but those are not all that different than TB3 since USB4 is mostly just rolling in TB3 with USB 3.x. There's the kind that use Thunderbolt 3, or TB3, to communicate with the host. There's the kind that use USB 3.0, 3.1, or 3.2, which I will refer to as USB 3.x from here on, to communicate with the host.
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