My USB hub has 4 ports for device connection, and one extended cable than can go into power. None of the 4 ports are connected with any device now.

If I connect the extended cable with PC (which cable is only meant to go into power) , the hub lights up and is recognized by the Windows 7 Device Manager. My mouse and keyboard would work just fine with the hub.

Alternatively I could also use one of those USB male-to-male wires to connect one of those 4 hub ports directly with my PC. Then the hub would light up, but would not be recognized (not even a message indicating that). No mouse or keyboard could be used with the hub either. The mouse would light up, the keyboard's NumLock Led would not. Even I have made that extended cable go into power, but it's no use.

How to explain that? This would be one of a series of questions since I am debugging a home network. Hope that this would not be considered a silly question, I do not have a decent knowledge about Hub Mechanics.

The USB hub

  • a pic or link to a pic, may be helpful.. your terms like "extended cable" and "go into power" are rather unclear and untechnical – barlop Nov 15 '16 at 2:31
  • It might help if you link to some pictures of the hardware and cables and describe what you're trying to do, or add a diagram. The "cable that goes to power that you can plug into your PC" lost me; no idea what you're referring to. There should be a USB cable that goes from a USB port on the computer to the input port on the hub, and that's for both (limited) power and the data connection. You can't plug the computer into one of the hub's output ports. Didn't the hub come with a user manual or diagram? – fixer1234 Nov 15 '16 at 2:31
  • @fixer1234 The hub was one lying around, and I can't remember if it came with a manual. I think you clarified that the extended cable I specified is really the only one that would go into my PC, and so my PC would be the only power source of my hub, even if that source only provides limited power. Then, of course, I was under the wrong impression that the hub could be externally powered by an AC/DC adapter. But such an external power source I desperately needed, to operate a WiFi adapter along with my input devices. – Tony Marshle Nov 15 '16 at 4:18
  • @TonyMarshle, could you try to understand that besides power, the hub needs some data lines working as well? How do you think the data to/from your wi-fi are getting to your PC? – Ale..chenski Nov 15 '16 at 6:55
  • @Ali Chen Yes, fixer1234 clarified that only the extended cable is to connect to the PC; and this is no power issue: it is the way the data line works. Through the hub my WiFi adapter does not operates, but this is a separate issue (which I suspect is a power issue). I actually wonder if this could be resolved by powering the hub with an AC/DC adapter. – Tony Marshle Nov 15 '16 at 7:25

Alternatively I could also use one of those USB male-to-male wires to connect one of those 4 hub ports directly with my PC. ...
How to explain that?

You're trying to misuse/mis-connect the USB hub. The ports in the USB hub are not equilvalent.

What you call the port for the "extended cable" is specifically designated the upstream port that is supposed to be connected to a USB host (master) port.

The other four ports are specifically designated the downstream ports for connecting USB slave devices (aka gadgets).

These designations are fixed by the USB controller IC embedded within the hub.

It's simply wrong to connect a downstream port to a USB host.


Your terms your terms like "extended cable" and "go into power" are rather unclear and untechnical.

In fact some USB hubs can be powered by an ACDC adaptor, but that aside.

It seems you know how to use it (which ports are meant for usb devices and which is meant to be connected to the computer), but as an experiment you have tried connecting a computer to a port meant for a usb device, and that hasn't worked, and you want to know why.

I suppose the logical reason why it doesn't work is if A,B,C,D are hub ports. A= port for computer B,C,D are the other ones. It's designed so A communicates with B,C,D. But B,C,D don't communicate with each other. So if plugging a computer into B or C or D then a device into one of the remaining of B/C/D then the computer won't communicate with the device


Alternatively I could also use one of those USB male-to-male wires to connect one of those 4 hub ports directly with my PC.

No, you can't use "alternatively" the downstream ports of a hub. There is no alternative. A USB hub is a "directional" device, it has an "upstream port" (to be connected to PC host, and only to PC host), and several "downstream" ports, to be connected either to more hubs, or to USB peripheral devices. The downstream ports have the HOST FUNCTION, they supply power and control peripheral devices. The USB has "star" topology, it has one host, and everything gets branched out. Don't confuse USB with a symmetrical full-duplex Ethernet switches. It is not a "network" as you imagine it.

Your hub is apparently on the very cheap side, and has unprotected "ganged" power wiring. The idea is that it gets the power from either a wall adapter, or from VBUS from host cable. When you plug wrong cable into downstream port, the hub gets powered, yes, but from a wrong way.

How to explain that?

You are not supposed to ever use the "male-to-male" dongles or "male-to-male" cables. They are outside USB specifications, specifically for the very reason - so a user cannot connect a PC host port to another host port, either another PC or downstream ports of a hub. For the very same reason the upstream port in hubs has either a Type-B connector (or non-detachable A-plug). When you plug the male-male cable between PC and downstream port, you are setting an electrical conflict, host against host. That's why nothing works when you try this.

It is strongly advisable to get some USB basics before wasting too much time experimenting on wrong assumptions. Unfortunately, there are no non-technical interpretation of USB, the best I know of is this one.

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