USB Hub topology

[Phil1977]

Hi,

I have a question that google couldn't answer me precisely (or I didn't find the right buzzwords...).

Does a USB 3 hub route USB 1 and 2 signals *only* through it´s USB 2 host connection or are there hubs that "translate" from USB 2 to USB 3?

In other words, if I connect two USB 2 High-Speed-Devices (480MBit/s) to a USB 3 Hub connected with 5GBit/s to the host, can I expect them to simultaneously get their max. datarate?

If this is an extraordinary feature, what is its common name?

[Someone]

One keyword is aggregation.

Or just go to the solution:
https://hackaday.com/2022/03/07/a-chip-to-address-the-fundamental-usb-3-0-deficiency/

[Howardlong]

Hi,

I have a question that google couldn't answer me precisely (or I didn't find the right buzzwords...).

Does a USB 3 hub route USB 1 and 2 signals *only* through it´s USB 2 host connection or are there hubs that "translate" from USB 2 to USB 3?

The short answer is yes, unless it's a root hub.

USB 3 SuperSpeed connection has both 5Gbps SS and 480Mbps HS wiring compatible with USB 2.0, and they are on physically separate wires.

A USB 3 hub has both an SS and an HS hub. All the HS (and FS & LS) traffic goes over the HS hub, and all the SS traffic goes over the SS hub.

HS traffic is not "upgraded" or translated to SS traffic.

This is unlike an HS hub that will translate FS and LS traffic to HS traffic using one or more transaction translator(s), or TT.

A common problem with most HS hubs is that they only have one TT, so can't aggregate total FS bandwidth over 11Mbps. A multi TT USB HS hub will, though they're rarely advertised as such.

Conversely, it is fairly common for USB SS hubs to have multiple TTs that allow aggregating total FS bandwidth to over 11Mbps but that will still be be carried over the HS wiring.

In other words, if I connect two USB 2 High-Speed-Devices (480MBit/s) to a USB 3 Hub connected with 5GBit/s to the host, can I expect them to simultaneously get their max. datarate?

Typically not, although this one seems to claim to "The Multiple Transaction Translator (MTT) design prevents speed limitations, enabling multiple high bandwidth devices to operate at SuperSpeed."

I would be sceptical though, as the terminology "TT" is a USB HS thing, not typically associated with USB SS.

If this is an extraordinary feature, what is its common name?

VL670 or VL671 chips will convert a USB HS device into a USB SS device.

[magic]

It also says "Multiple Transaction Translator (MTT) design prevents data rate bottlenecks when legacy USB devices are attached".

So dunno, but it's probably exactly what the name implies: a multi-TT hub, so your multiple keyboards and mice will enjoy a combined 480Mbps BW.

There is no HS-SS translation in the spec and so such thing as SS TTs, so no particular software support for it either. A hub with multiple HS ports on SS bus would need to handle all protocol differences transparently and pretend at least to some extent that the devices are SS.

Note that there is some mechanism (forgot its name) for aggregating two 5G devices on a 10G hub.