USB Tiers
When setting up a USB connection, it’s important to keep in mind that there are limitations to how many tiers can be used. The USB standard allows for a maximum of 7 tiers, also known as levels or hubs, which determine the hierarchy of devices in the setup.
When a USB device is connected, two tiers are created — one for the USB device and the other for the host controller, such as a PC or a laptop. Every time the connection passes through a hub, additional tiers are established. The addition of each hub chip results in an extra tier.
The challenge lies in keeping the solution design within the specified tier structure.
Hub configurations are not always limited to the standard 1 to 2, 1 to 3, or 1 to 4 configurations. Hubs can sometimes be established in unexpected locations, such as when extending a cable beyond the USB standard or duplicating ports. It may not always be obvious when a hub is being used, and as a result, one may not realize when a new tier is formed.
When the number of tiers in a USB setup exceeds 7, the host controller (typically a laptop or PC) will not recognize the device and will not enumerate.
Here is a diagram showcasing the USB tier configuration of the Logitech Swytch product, which uses hub technology. To connect multiple devices, an additional 3.0-powered hub is included with the Swytch. This allows for the connection of a DSP Audio Solution and a Rally Camera in a Bring-Your-Own-Device room.
As you can see from the diagram above, only six out of the seven tiers are being utilized. From my perspective, it’s not recommended to fully maximize the tiers in a BYOD solution. This is because it’s uncertain whether the connected laptop is using port replication or not. Port replication is a method of adding extra USB ports that the laptop’s motherboard may not have. If a port replicator is used, it will add an extra tier to the setup.
USB hubs
To expand the number of USB devices you can connect to your computer, a USB hub is a useful addition that provides additional ports. When all USB ports are occupied, a USB hub or port replicator can serve as a viable solution. USB hubs and port replicators always create a new USB tier.
Extending USB Cables
There are several options available for extending USB signal over longer distances and overcoming the length limitation of USB cables. These options include USB extenders, passive USB cables, and active USB cables which allow for greater coverage without signal loss.
The USB standard was initially created to enable easy connections between desktop computers and peripherals like printers, storage devices, mice, and keyboards. Back then, these devices were typically situated near one another. However, today, USB cables are utilized for many applications beyond the desktop environment.
In the past, video conferencing systems were usually set up in meeting rooms or specific areas where people could be physically close to the equipment. In today’s hybrid work environment, virtual meetings and remote work have become the norm. To facilitate video conferencing from remote locations, it is common to connect USB cameras, microphones, and speakers to laptops or desktops. However, this often requires the use of USB extenders to ensure high-quality audio and video signals over longer cable distances. This is particularly important when implementing BYOD (Bring-Your-Own-Device) solutions.
Different Methods of Extending USB Cables
Passive Cables
USB cables that are passive, meaning they have no signal amplification or regeneration, are susceptible to signal degradation and interference. However, there are purpose-built passive cables with thicker cables and better shielding that allow USB signals to travel longer distances than standard cables, particularly those exceeding the recommended maximum length. Based on my observations, it would not be wise to exceed the USB standard recommendations when extending a passive cable.
Active Cables
Active cables use circuitry to regenerate signals, often at the receiving end, enabling data transmission over longer distances. They usually run on bus power and may need an extra AC adapter or USB-A connector to ensure the signal booster has sufficient power for longer connections. When each transceiver in the chain has access to power, active cables can be daisy-chained.
Did you know that USB cables labeled as “active” have hub technology and signal regeneration circuitry in a single port? This makes them function as signal boosters, improving the strength of the signal. You can use these cables to extend the effective length of a USB cable by positioning them along the cable and utilizing the hub technology. Adding active cables to the setup will increase the USB tier count by at least 1.
For example, the Logitech USB strong cable would be considered 1 tier because it is an “Active” cable.
USB Extenders
USB extenders are designed to extend the length of USB cables without the need for an extra tier. They function by emulating standard USB cables, but some models also include USB hub chips. It’s important to confirm with the manufacturer whether an additional tier is added by the exenter.
Many USB over Cat5 or Cat6 extenders function as solitary port hubs. They convert the USB signal into Ethernet and send it through a regular category cable. At the receiving end, this process is reversed, and the signal is transformed back into USB. It’s worth noting that most of these devices will add an additional tier.
USB Devices
Sophisticated USB devices like DSPs or the Logitech Rally often come with built-in USB hub tiers or layers, like the Display Hub and Table Hub. If used as an independent camera, the Rally Camera receives power from a power splitter that uses hub technology to inject power into the USB connection. The Power splitter will add 1 tier.
Additional information:
-Certain computers and laptops may have an internal or external hub layer built in. One such device is the Lenovo ThinkSmart Hub Gen 2, which features an in-line USB hub on each USB port within its integrated cable.
-If a configuration surpasses the limit of the USB layer, the final layers/devices usually do not enumerate, leading them to not show up in the Device Manager. This could be incorrectly interpreted as a faulty product.
-It can be difficult to identify USB layers during diagnostics as they may not always align directly with physical components. To check USB tiers, it’s best to follow these methods.:
To check your USB on a Mac, go to the Apple menu, select “About This Mac,” and then choose “System Report.” From there, you can access information about your USB.
On a Windows computer, you can use Microsoft’s USBView to view your USB details.
