USB controller(s) driving USB ports on TBT3-UDZ

Thunderbolt 3 TBT3-UDZ
#1

In the TBT3-UDZ specifications, it lists the USB ports as such:
image

Does this listing correspond to the number of underlying USB controllers in the dock driving the ports (with the ports in each line sharing the bandwidth of the controller/USB speed), or is it just an inventory of ports (that might have a different configuration of underlying USB controllers/shared bandwidth) and if so, what is the actual underlying configuration?

E.g., if a user plugged in 4 different USB-to-SATA SSD drives (each capable of 5 Gbps/~500 MB/s throughput) in to the USB-A ports in the rear, would the drives in aggregate be capable of 20 Gbps/~2000 MB/s throughput (that, up to the PCIe x4 limit of the Thunderbolt uplink)? Or maybe just 5 Gbps/~500 MB/s, if all 5 rear ports share the same 5 Gbps USB controller – or somewhere in between if maybe the sharing falls at different ports?

Likewise for the two 10 Gbps ports on the front. Do they share bandwidth between each other, or are they independent 10 Gbps channels that could be fully used (again up to the PCIe x4 limit of the Thunderbolt uplink), like say if each had a USB 3.1 Gen 2 attached NVMe disk attached?

Thanks for any clarification!

#2

Hello!

Thanks for asking! I’d be happy to assist.

The list is an inventory and not representative of port to controller mapping. Due to how the Intel Titan Ridge Thunderbolt 3 reference design is configured, all USB traffic is routed through the same USB 3.2 Gen 2 10Gbps hub chipset in the dock. So bandwidth is shared for all external USB ports and for internal USB devices (Ethernet, audio, card reader).

Computer --> Dock Thunderbolt 3 chipset --> Dock USB 3.2 Gen 2 hub (x1) --> Dock USB 3.0 hubs (x2)

So there’s a total of 1250MBps (10Gbps) of USB bandwidth on paper (not accounting for any overhead).

Please don’t hesitate to let us know of other questions.

Thanks again for contacting Plugable support and best wishes!

Joshua Henry
Senior Engineer | Product Owner
Plugable Technologies

#3

Interesting. I guess that’s the trade-off of the Titan Ridge USB backwards compatibility – hang everything off a single USB 3.2 chipset, or have any PCIe-attached devices disappear when connecting upstream via USB.

So, if everything on the TBT3-UDZ (aside from the DisplayPort) routes through a 10Gbps USB link, even if connected via Thunderbolt 3, would it be OK then to connect the dock to the upstream computer via a passive 2m 20 Gbps TB3 cable (like the Plugable TB3-20G2M, https://plugable.com/products/tbt3-20g2m ), without any performance loss?

#4

That’s absolutely correct!

Dual monitors via Thunderbolt 3 operation of the dock will still require a 40Gbps cable, but a single monitor via Thunderbolt 3 operation would work fine with a 20Gbps cable and USB bandwidth shouldn’t be affected.

USB-C only systems without Thunderbolt 3 can support two monitors via a 10Gbps USB 3.1 Gen 2 cable. This is enabled with the use of DP MST (DisplayPort multi-stream) for the two displays, and USB traffic is limited to 5Gbps.

Best wishes,
Josh

#5

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