Understanding the "Multi-TT switched USB architecture" Hubport feature

Newer Hubports, such as the compact ("c") models and the Hubport/14 are USB 2.0 hubs that offer a feature called Multi-TT switched USB architecture. This article is intended to explain how much bandwidth the USB 2.0 Hubports offer and what exactly Multi-TT means.

About USB 2.0 Hubports, assuming that the USB port of the PC that the USB 2.0 Hubport is attached to is a USB 2.0 port, the upstream link on any of our USB 2.0 Hubports is 480 Mbps. The aggregate bandwidth of all ports on the hub cannot exceed 480 Mbps at any given instant.
If you have a high speed transfer going at 480 Mbps and add simultaneous activity on any other port, the high speed performance will be reduced by that amount. However, statistically, that almost never amounts to very much, as the slower speed devices send in blocks, not continuous. It certainly will not drop the high speed port to 12 Mbps.
The essence of the Multi-TT switched USB architecture is that, regardless of whether you have a high speed transfer going on or not, the other ports will get their 12 Mbps guarantee. In other words, one high speed port cannot "hog" all the bandwidth.

Last updated: Jul 09, 2019

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