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I want to connect 4 USB peripheral devices to two computers using a USB Switch. One of the devices is a Cam Link 4K HDMI to USB 3.0 converter (i.e. I want the HDMI camera stream available (one at a time) to the two computers).Cam Link 4K

The other items I wish to switch are all USB 2.0 devices, e.g. mouse, keyboard, audio interface.

I am looking at USB 3.0 switches. I have noted that some have USB 3.0 A ports to connect to the computers, like this UGreenUGreen USB switch with USB3.0A ports.

Another device uses USB 3.0 B ports to connect the the computers, like this Rosewill: enter image description here

Q1: Am I likely going to be able to successfully switch a video device through a USB 3.0 switch like these examples? If not, what is the primary technical reason? (assume that I am an electrical engineer with a networking background, but no direct experience with the tech details of USB.)

Q2: Given that these devices are essentially switchable USB hubs, is there any reason to choose the type B ports instead of the type A ports?

Many thanks!

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  • USB-A are probably used because USB 3.0 USB-B ports are way too bulky. USB 3.0 Micro-USB-B ports are not as physically durable.
    – Daniel B
    Commented Jan 6, 2021 at 13:37
  • " USB-A are probably used because USB 3.0 USB-B ports are way too bulky. USB 3.0 Micro-USB-B ports are not as physically durable. " Use of USB-A also means the device violates the USB spec. That's like the electrician that's too lazy to run ground wire or put in a GFCI and puts in an ungrounded 3-prong outlet anyway. It will work, until it doesn't, and someone gets hurt. USB doesn't have enough power to hurt anyone directly but it can start a cable on fire by connecting two live USB-A ports together. If they are willing to violate the spec so visibly then who knows what is inside.
    – MacGuffin
    Commented Jan 6, 2021 at 17:45
  • Look, it’s just a fact. Using USB-A on the device was relatively popular in the early days of USB 3.0 simply because the USB 3.0 B connector is too bulky for many devices like 2.5″ external HDDs.
    – Daniel B
    Commented Jan 6, 2021 at 21:33
  • " Look, it’s just a fact. Using USB-A on the device was relatively popular in the early days of USB 3.0 simply because the USB 3.0 B connector is too bulky for many devices like 2.5″ external HDDs. " Also a fact is this practice violates the USB spec. Another fact is using the cable needed for this violation to work here anywhere else could damage the cable and/or the ports connected to the cable. People so blatantly violating the spec in one case cannot be trusted to not violate in other cases. Such hardware should be avoided. It's penny wise and pound foolish to buy this junk.
    – MacGuffin
    Commented Jan 6, 2021 at 22:52
  • Do they not make type-B ports which could be mounted sideways?
    – grawity_u1686
    Commented Jan 7, 2021 at 19:56

3 Answers 3

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Q1: Am I likely going to be able to successfully switch a video device through a USB 3.0 switch like these examples?

I would say yes, because traditional type-A/B ports didn't have any special "alternate modes" for video capture, so there is nothing special that a hub/switch would need to support – if your stick is a USB device then it's a USB device.

Q2: Given that these devices are essentially switchable USB hubs, is there any reason to choose the type B ports instead of the type A ports?

I would ask the opposite: why does the first hub use a type-A port?

It is normal for a hub's "upstream" (computer-facing) port to use type-B, and it exactly fits the original USB design where hosts use type-A ports and devices use type-B ports, and every cable is A-to-B (with A-to-A cables being outright forbidden in USB 2.0). The hub's downstream ports are type-A because they too connect to type-B ports on your devices.

Recall, original USB was designed to be strictly directional, with type-A ports supplying power and type-B ports receiving power – completely unlike (modern) Ethernet or USB type-C where devices negotiate which side does what.

So when your first example hub uses type-A for its upstream port, that looks fairly odd to me, and a bit suspicious. Even though special A-to-A cables do exist in the USB 3.0 standard1, they are specifically not meant to connect a computer to a hub, and this port misuse raises questions about whether anything else about that hub is standards-compliant. "It's not illegal" is not exactly a glowing recommendation.

1 (They are special because they only have the USB 3.0 data pins wired up, while the USB 2.0 data+power pins are left unconnected to avoid setting your desk on fire.)

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Q1: Am I likely going to be able to successfully switch a video device through a USB 3.0 switch like these examples? If not, what is the primary technical reason? (assume that I am an electrical engineer with a networking background, but no direct experience with the tech details of USB.)

This should work and the switching should be no different than removing the USB devices physically from one computer and connecting them to the other.

Q2: Given that these devices are essentially switchable USB hubs, is there any reason to choose the type B ports instead of the type A ports?

You choose the one with the USB-B ports because USB-A ports as inputs violates the spec for connecting any USB 2.0 devices and is only allowed under USB 3.x when connecting USB-A host to USB-A host. Such cables for USB 3.x host to host connection by USB-A are somewhat of a specialty item, used for Windows and Linux kernel debugging for one. The USB switch with USB-A ports as inputs cannot meet the spec since the switch is not a USB 3.x host.

The only way this complies with the USB spec would be in a way that does not allow the use of USB devices, only connection to other USB hosts. If they mean "switch" like "Ethernet switch" where the switch is automatically diverting packets to their intended destination then maybe this somehow complies with the USB spec but that again does not match the intended use of plugging in USB 2.0 and USB 3.x devices.

If you are looking to switch mouse, keyboard, audio, and USB devices then I believe you are looking for a KVM switch, not a USB switch. Look for a KVM switch that allows for the switching of USB 3.x devices. Here's one example: https://www.startech.com/en-us/server-management/sv231dpu34k

That link is not an endorsement of the specific device. I used StarTech KVM switches before and they appear to work well enough. I don't have much experience with the competition to know if there is better stuff.

The KVM in "KVM switch" means keyboard, video, and mouse. These will switch video (HDMI, DisplayPort, VGA, or whatever) with the USB ports. It sounds like this might be useful for you, if not then it may still be a wise choice because these will have been built for your intended use and not for whatever use that UGreen device is for. The only use I see for that UGreen device is to separate people from their money and leave them with something that will likely not work, or not work and damage USB ports on computers.

If there were not so many junk USB switches out there then I might not be so against them. Because so many of them are junk I assume all of them are junk.

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  • I know what a KVM switch is, but discounted it because I can easily run separate video cables from each computer to the monitor and switch inputs on the monitor. Adding video switching to this USB switch device increases costs. Also, I have more confidence in the switch in my nice Dell monitor than some inexpensive, no-name device. Many thanks for your explanation!
    – klaberte
    Commented Jan 7, 2021 at 17:33
  • " I know what a KVM switch is " Okay, but I described it for those that might not. " but discounted it " Then perhaps you should reconsider. A quality USB switch is not going to be all that much cheaper than a quality KVM switch. I tried switching the video separate from the USB and that became frustrating quite quickly. Whatever you saved on not getting a KVM switch will be quickly forgotten after having to push multiple buttons when there's something that makes the process easier, faster, and less error prone (switching one but forgetting to switch the other).
    – MacGuffin
    Commented Jan 8, 2021 at 3:35
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Am I likely going to be able to successfully switch a video device through a USB 3.0 switch like these examples? If not, what is the primary technical reason? (assume that I am an electrical engineer with a networking background, but no direct experience with the tech details of USB.)

Tldr: In this case- yes, because its not a video device. Its a webcam.

The easiest way to think of this is that its a "monitor" on one end, and a "webcam" on the other. Your device takes HDMI on one end (emulating a monitor), does some magic, and dumps it out to a chip that takes that video stream and converts it to a standard webcam video stream. Your video source, and the device you are outputting the video to are even unaware of each other.

(i.e. I want the HDMI camera stream available (one at a time) to the two computers).

So in this case - you're essentially using your switching hub to switch a webcam between PCs - that's trivial and should work. You are not switching a video device. You are switching a USB webcam. There is no alternate stream, or any complicated thing going on. As far as your PC is concerned, it is a 'simple' standard USB device. I own a cheaper model, and they're absolutely lovely for certain uses. In this case though, for once, things are simpler than you think they are.

I am looking at USB 3.0 switches. I have noted that some have USB 3.0 A ports to connect to the computers, like this UGreen

USB A on the device side is against spec as per the other answers. That said, I suspect the manufacturer went for it because its slimmer and saves on bill of materials, and presumably is 'easier' to build since its one part, not two. Caveat Emptor

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  • You lost me on "Your device takes HDMI on one end (emulating a monitor)". Monitors receive video content, not produce video content.
    – klaberte
    Commented Jan 7, 2021 at 17:27
  • So PC( or camera's) HDMI out goes into the device HDMI in. Your PC detects it as a monitor. It then processes it, and outputs as a device detected as a webcam.
    – Journeyman Geek ♦
    Commented Jan 7, 2021 at 17:32

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