A USB hub will not function when it’s connected more than 5 hubs away from the root port

kvm-switchmicrosoft-surfaceusbusb hub

I am trying to utilize my monitor's ability to switch video input and USB source (much like a KVM switch) with a USB hub. Previously I had all of the devices plugged directly into USB ports on the monitor. I could switch video input on the monitor to the Surface via its dock or the desktop (both machines are running Windows 10) and USB switched along with the video.

Since introducing the USB hub the Surface dock no longer works with USB, but the desktop does. If I bypass the dock and plug a USB cable directly into the Surface it too works. When connected through the Surface dock I receive the error:

Too many USB hubs are connected together. A USB hub will not function when it's connected more than 5 hubs away from the root port.

The desktop is a generic PC but since the Surface is having issues I've specifically called it out in the list of devices in my configuration:

If I read the error explicitly I can only count 4 USB hubs: Surface Book, Surface Dock, Monitor, and USB hub. To explain how I have things hooked up I've put together this diagram:

Diagram of configuration

Until this error I was under the impression that powered USB allowed for 127 devices to be daisy chained. Is this impression incorrect or is something wrong with my configuration?

Additional info based on responses:

My USB Hub chain as viewed with USB Tree Viewer when connected to my Surface Book via the Surface Dock:

USB Tree Viewer screenshot of Surface Dock hub connections

From this I definitely see that there are more than 5 hubs from the root port to the devices at the end. It seems that a "single layer" hub at the end would solve the issue. According to Ali Chen's comment "finding this information in marketing documents" would be unlikely.

Best Answer

When counting hubs, you assume that every individual box/device has only one hub. This assumption is likely untrue.

To begin, the 10-port "amazon hub" definitely has at least two hubs in chain, because single hubs are not manufactured with 10 ports, 7-port maximum [see this explanation].

Then the Dell monitor has also some special design - it has TWO UPSTREAM ports. What is its internal architecture, who knows.

The "surface dock" is also a suspect for having more than one USB hub in the chain. And I don't know if the "surface" uses extra internal hub for whatever reason.

To get the actual idea how many hubs are there in the chain and what/how all things are connected, use USBTreeView.exe on the Surface side. I am sure the Surface got the chain right, and you do have more than 5 hubs in the chain.

Addition: USB standard allows for 127 devices per one root controller, it doesn't mean that they are "daisy chained", just total of 127. In fact, if we discount hubs as functional USB devices, the total number of useful devices comes down to 102, since you would need 17 7-port hubs to accommodate the devices, in three-tier configuration, and each hub will take one address out of available space.

Related Question