Installation: USB hub chains in video conference room

Owned by Olof Ermis
Last updated: Aug 21, 2024 by Torbjörn Karlsson
4 min read

When USB standard was developed back in the 90’s it was design for connecting accessories like mouse and keyboard to your computer. The USB hub was part of that to ensure that several devices could be connected. For that use-case, having max 5 usb hubs daisy-chained and a maximum of 127 USB devices connected to laptop was at the time considered way more than enough. How anyone would need so many hubs and devices at their desk?

Fast-forward to today and the highly USB-based video conference systems that are currently installed and this is right now one of the main issues facing larger deployment of video conference rooms.

Background

 

At first glance, having 5 hubs seems to be more than enough also for a video conference system, but to better understand the issue, we need to look into how a modern BYOD or MTR video conference room is designed and how the included devices uses hubs. Also note that the max 5 hub hops is the same for USB 2.0 and USB 3.2 and normally these two functions are co-located in the same hub (but there is exceptions, see below).

At a second glance however, problem starts to happen due to how each of the components in a modern video conference room is using USB hubs internally. Not normally a problem when the product is used standalone, but it becomes a problem when they are all connected together. The above pictures shows a not uncommon system design which has 8 hubs in a chain and will fail 100% of the time. Let’s look at each component:

Internal USB hub overview

Laptop

In a laptop, there are internal USB hubs to ensure that you get enough of USB ports and many of the internal function in a laptop such as touchpad and camera are also internal USB devices. Normally, these hubs are defined as USB Root Hub and that hub doesn’t count towards the max 5 hub limits. However, there are more and more laptops coming out that have an additional hub which is NOT a root hub, e.g.

  • MacBook Pro M-series (all versions)

  • Other ARM-based laptops and Chromebooks

  • And a few Intel-based laptops as well

Given this, to ensure that the video conference room works with 100% of all laptops, the max available hubs are 4.

USB-C Docking Stations

Regular USB-C docking stations normally have lots of external USB ports and also internal USB devices. Since the standard for a USB hub is 4 downstream ports, they always use at least 2 daisy-chained hubs internally. It can be a bit random how the external USB ports and the internal hubs are connected so important to keep track of the actual product and port used.

Extension system and active cables

  • Ethernet-based extension solution for USB have basically always at least one internal USB hub and in many cases there are 2, one in both transmitter and receiver.

  • Electrical active USB cables basically all handle extension of USB 2.0 through the use of additional USB hubs which acts as re-drivers of the signal.

  • Active Optical Cables (AOC) have almost always at least one and often two internal hubs, integrated into each connector.

Interactive display or additional wall-side usb hub

Sometimes there is a need to add multiple USB devices on the wall-side of the room and if an AOC or electrical active cable is used, this is often the case. If an interactive display is used, it might be tempting to reuse that as an USB hub and at the same time connect the internal touch function of the display However, due to the nature of how interactive displays deals with switching between the built-in computer and external USB ports, they have almost always at least two daisy-chained hubs between the USB input and the USB-A output ports.

Integrated hubs in end-device

Something which is often overlooked is the fact that the majority of the regular USB video conference devices on the market have internal hubs as well. Most of the videobars but also strangely enough many separate cameras and audio devices as well.

Additional importart note

As mentioned, USB 2.0 and USB 3.2 usually shares the same hubs and both standard have the max 5 hops as the maximum. However, this is not mandatory in the standard, and in some products there are more additional USB 2.0 hubs than USB 3.2 hubs, e.g. in active electrical cables and certain USB-C switches on the market. Since a camera might connect via USB 3.2 and audio device or touch function in an interactive TV will normally connect via USB 2.0, the result can be that the camera works, but the laptop (a MacBook Pro for instance) can’t access the audio devices or the touch-back function.

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Best practice for Pro AV designers

In principle, there is only one approach here. The AV designer needs to know how many internal hubs each component has internally to ensure that the it is not more than 4 hubs daisy-chained in total. If the room is targeting only limited and known Windows-based laptops, it could be ok to be allowed to use 5 hubs.

Since this information is never included in the data sheets, the best way to handle this is to download the tool USB Device Tree Viewer (https://www.uwe-sieber.de/usbtreeview_e.html ). It is a free tool developed by Mr. Uwe Sieber. It shows the entire USB tree structure from the laptop’s point-of-view and also USB 2 and USB 3 structures separately.

Using this tool, each device can be connected and it is easy to see the number of hubs that each component adds.

 

 

 

 

 

 

 

 

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