USB Tiers - A Guide to Compatibility

During compatibility testing, we have identified the following potential issues when using all-in-one screens and USB switchers.

Outline of issues

When using a USB switcher with active cable, it is possible to exceed the maximum number of USB Tiers (levels / hubs)

The total permitted number of USB tiers is 7. This is set out in the USB standard. In theory, this limitation shouldn’t be reached, but as laptops develop and AV installations make greater use of USB devices, it is possible to exceed the limit.

In our tested scenarios we used 2 different makes of Windows 11 laptops, 4 switches and 4 screens.

- A laptop computer typically users 2 or 3 tiers, depending on complexity of internal USB.
- A USB Switcher uses 2 tiers
- An Active USB Cable uses 2 Tiers
- An All-In-One screen with built-in camera, speakers and microphone will use 2 or 3 Tiers
Symptoms

If the total number of USB tiers is exceeded, Windows 11 machines will typically display an error message ‘USB device not recognised’ or ‘Maximum USB Hubs Exceeded’. Occasionally, a “silent failure” will occur and no error is displayed. However, in Device Manager, a USB Hub will be shown in fail state.

USB devices on the All-In-One screen will not be accessible via the USB switch (microphone, camera, speakers and touch back).

Fig 1. In this scenario, the laptop will not see any of the peripherals on the AIO screen

How to determine if you have this issue

Whilst you can check within Windows, we downloaded a USB Diagnostic tool to provide more detailed information. There are lots available, but we used the Liteware USB20 Configurator app.

Potential Workarounds

Because this is a fundamental restriction of USB architecture, there is no ideal solution. However, options may include:

Option 1.

Using a passive USB connection to the laptop (USB-C <3m in length). This may mean that the USB switch needs to be positioned under the table rather than behind the screen. In this case, consider a TX/RX unit to minimise cabling.
This will provide access to all peripherals on the AIO screen, including touch back. However, you will lose the benefits of Active USB-C and not get power or network to the laptop.

Fig 2. In this scenario, the laptop will see the peripherals of the AIO screen, but cable USB cable length is restricted to 3m. This will not get full benefits of Active USB-C (no power or network provision).

Fig 3. In this scenario, the laptop will see the peripherals of the AIO screen. RX unit is mounted on the table so USB cable length is less of a problem. This will not get full benefits of Active USB-C (no power or network provision).

Option 2.

Do not use the peripherals on the AIO screen. Separate USB peripherals may be a better solution in the space. Touch back will not be supported

Fig 4. In this scenario, the laptop sees the additional USB peripherals. Using external peripherals may offer a better experience. As there is no USB connection to the screen, touch back is not supported.

Option 3.

Instead of an All-In-One display, switch to a screen without built-in USB devices. We have tested with Jupiter and TeamBoard touch screens and touch back is fully supported.

Fig 5. In this scenario, the laptop sees the additional USB peripherals and has touch back with the display. Full USB-C functionality is preserved

Option 4.

On certain AOI screens, it may be possible to disable certain USB functions to reduce the number of USB Tiers utilised. However, this has not been field tested and is not recommended as it may impact functionality of the solution.

Products Used in Testing
Switches

ReThink 2 x 1 / 4 x 1 / 4 x 2

Liteware 4 x 1

Screens

MAXHUB XBoard

Jupiter 81T / 105T

TeamBoard 65FX

Notification