MPX 250

Overview

The MPX 250 platform features a modular USB-C distribution system designed to facilitate screen sharing from participants and to route USB signals from peripheral devices (e.g. a camera bar) to one or more host computers (e.g. laptops).

It consists of three primary components:

MPX 250
MPX 250 DC
MPX 250 EXT

These components can be flexibly combined to support a variety of room configurations. However, it's important to consider potential USB chain limitations, particularly those related to the number of USB hubs in the path.

Screen sharing

With the MPX 250, screen sharing is enabled via USB-C DisplayPort Alternate Mode (ALT DP Mode), a feature of the USB-C standard that allows a single USB-C port to transmit native DisplayPort video and audio alongside power and data over the same connector.

DisplayPort Alt Mode is always possible regardless of the length of the USB chain, provided that all components in the connection path are compatible with the ALT DP Mode.

Connecting USB peripherals

When connecting USB devices (such as DSPs, cameras, microphones, or speakers) instead, the USB specification imposes a strict limitation: no more than five USB hubs may exist between the host and the peripheral. This constraint is commonly known as the “5-hub rule.”

Exceeding this limit may result in signal degradation, device enumeration failures, or complete communication loss. It is therefore essential to design USB topologies that fully comply with this rule.

The 5-Hub Rule

The USB specification allows a maximum of 5 hubs between a host (typically the user's laptop or a video conferencing system) and a USB device (such as an installed A/V peripheral). This limitation poses a significant challenge in larger or more complex video conferencing room deployments, where multiple USB extenders, switchers, or distribution elements are often required.

USB hub contribution of each MPX component

Each component in the signal chain may add one or more USB hubs, depending on how it is configured and connected. Understanding the hub contribution of each device is essential to ensure the total number of hubs does not exceed the USB specification limit.

Component	Image	Hub Contribution	Notes
MPX 250		1 hub (USB-C ports 1 or 2) 2 hubs (USB-C ports 3 or 4)	Ports 1 and 2 should be preferred whenever possible, as they provide the most direct USB path with minimal hub layers
MPX 250 DC		1 hub (USB-C ports 1 or 2) 2 hubs (USB-C ports 3 or 4)	Ports 1 and 2 should be preferred whenever possible, as they provide the most direct USB path with minimal hub layers
MPX 250 EXT		1 internal hub
Biamp Vidi 250/280		No internal hub
Biamp VBC 2500/2800		1 internal hub	The VBC 2500/2800 includes an internal USB hub that bridges the audio and video subsystems, presenting them as a single composite USB device to the host
Mac Laptop (M-series)		Adds 1 internal hub	All M-series MacBooks feature a built-in USB hub, which contributes to the overall hub count
Windows Laptop		No internal hub	Note that some Windows laptops do include internal USB hubs, with configurations that may also differ across ports on the same machine

Examples of valid USB chains

To illustrate how USB hub accumulation impacts topology compliance, the following examples present both valid and invalid configurations within the 5-hub rule limit.

In this scenario, a Parlé VBC 2800 is connected to the MPX 250, which in turn connects to a Windows or MacOS laptop.

The maximum total number of USB hubs in the chain is 4, which complies with the USB “5-hub rule”.

Chain breakdown:

Parlé VBC 2800 = 1x USB hub
MPX 250 on port 3 or 4 = 2x USB hubs
MacOS laptop = 1x USB hub

Total: up to 4x USB hubs

MPX 250 EXT + MPX 250

In this scenario, a Parlé VBC 2800 is connected to the MPX 250, which in turn connects to a Windows or MacOS laptop.

In this setup, a Parlé VBC 2800 is connected to a MPX 250 EXT, which in turn connects to an MPX 250 unit, and finally to Windows or MacOS laptops.

The maximum total number of USB hubs in the chain is 5, which complies with the USB “5-hub rule”.

Chain breakdown:

Parlé VBC 2800 = 1x USB hub
MPX 250 EXT = 1x USB hub
MPX 250 on port 3 or 4 = 2x USB hubs
MacOS laptop = 1x USB hub

Total: up to 5x USB hubs

MPX 250 EXT + MPX 250 DC + MPX 250

In this scenario, an MPX 250 EXT connects to an MPX 250 DC, which serves as the central hub. Two MPX 250 units are then connected, allowing support for up to 8 participants.

On the MPX 250 DC, it is recommended to use ports 1 and 2 whenever possible, as they avoid introducing additional USB hubs into the chain.

The maximum total number of USB hubs in the chain is 5, which complies with the USB “5-hub rule”.

Chain breakdown:

Vidi 280 = No USB hub
MPX 250 EXT = 1x USB hub
MPX 250 on port 1 and 2 = 1x USB hubs
MPX 250 on port 3 or 4 = 2x USB hubs
MacOS laptop = 1x USB hub

Total: up to 5x USB hubs

How to check USB hub depth in your system

Use the procedure below to confirm compliance with the 5-hub rule and detect any unintended USB topology issues.

Note that the total number of hubs in the chain may vary depending on:

Which USB-C port is used on the laptop (some may include an internal hub)
Which cable is used from the MPX 250 Table Controller (Ports 3 and 4 introduce an additional USB hub compared to Ports 1 and 2)

Windows

To verify the actual number of USB hubs in an installed system, you can use a tool such as the free "USB Device Tree Viewer" for Windows.

Follow these steps:

Download the free tool "USB Device Tree Viewer" from this link and run it.
Connect your laptop to one of the USB-C cables from the MPX 250 table controller.
Press the share button on the table controller so that the connected port is active.
On the left panel of USB Tree Viewer, count the number of visible USB hubs between the host controller and the final device.

MacOS

On MacOS, there's no need for third-party tools, the USB chain can be inspected using the built-in System Report utility.

Follow these steps:

Connect your laptop to one of the USB-C cables from the MPX 250 table controller.
Press the share button on the table controller so that the connected port is active.
On MacOS, go to System Settings > General > About, then click System Report.
In the left sidebar, under Hardware, select USB.
In the right panel, expand the USB Device Tree and count the number of visible USB hubs between the host controller and the final device.

Note: The internal USB hub present in Apple M-series Macs (e.g. M1, M2) is not explicitly listed in the System Report or USB device tree, but it does count toward the USB 5-hub rule and must be taken into account when designing the USB topology.

The same information can be obtained from the MacOS Terminal by running the following command:

system_profiler SPUSBDataType | less