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What happens if you connect two USB downstream ports with a USB male to USB male cable?

By rodion15
Aug 7, 2016
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  1. It may seem pointless, but there's a big chance that kids on a school computers connect a laptop to a desktop usb ports with one of the USB male to male cables around.

    To clarify the meaning of Upstream VS Downstream I just did this summary after I clarified it to myself:

    In telecommunications generally, a transmission from an information server toward an end user is referred to as downstream and a transmission toward the server is referred to as upstream.
    My summary:
    In USB terminology:
    Upstream port: Receives power, for example the Micro-USB port on a smartphone is an upstream port.
    Downstream port: Gives power, for example, the USB on an Apple keyboard is a downstream port.

    A computer has a number of downstream ports.

    On USB hubs, the port that connects to the computer is an upstream port, while the ports that connect to devices are downstream ports.
     

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  2. Cycloid Torus

    Cycloid Torus TS Evangelist Posts: 1,657   +309

    USB male plug A connector to male plug A connector: definitely non-standard...why would you have any? I know you can buy them on Amazon, but what good are they? Connecting two female receptacles? Pin 1 will be +5v, so it would be like to 5v batteries in parallel (same voltage, more capacity).

    Some folks might try these as transmission cables. Belkin sells it and apparently it works, but my guess is that the software is essential to manage the non-standard handshake ( https://www.amazon.com/s/ref=nb_sb_...&field-keywords=Belkin+Easy+Transfer+(F5U279) ).
     
  3. EndlessWaves

    EndlessWaves TS Booster Posts: 164   +34

    IIRC the spec says A to A and Male A to Micro A cables don't exist. All client devices were originally connected by captive wires or B connectors and more recently micro-B, OTG (Micro-AB) and Type C connectors.

    The transfer 'cables' are probably devices with two cables coming out of them rather than some sort of special ethernet-style crossover cable.

    If it is nonstandard then who knows? I guess there's probably some sanity checking in a lot of USB controllers but it could potentially cause damage.
     
  4. jobeard

    jobeard TS Ambassador Posts: 9,330   +622

    USB has not notion of Up vs Down stream (which is just the Router terminology for Data Provider vs Consumer).

    With USB 3.0, there is the intent that PC--USB--PC should be allowed as a faster alternative to Ethernet connectivity.
     
  5. Cycloid Torus

    Cycloid Torus TS Evangelist Posts: 1,657   +309

    Is there a software or driver piece to that?
     
  6. jobeard

    jobeard TS Ambassador Posts: 9,330   +622

    I don't think it's necessary
     

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