UD-3900 Slows Down My Gigabit Ethernet

I have the UD-3900 (Rev B2) docking station, which is plugged into a USB 3.0 port on my Lenovo T450s laptop. When I plug my ethernet cable directly into my laptop, I get download speeds of around 500 mbs. However, when I plug my ethernet cable into my Plugable docking station, the download speed maxes out at 200 mbs.

I thought the docking station supported Gigabit Ethernet and that the speed wouldn’t be slowed down by connecting the docking station to the USB 3.0 port on my laptop? Do I have an older version (Rev B2) that didn’t have Gigabit Ethernet? Any other possible solution?

Hi Derek,

Thanks for posting, and I would be happy to help with your docking station.

All versions of our UD-3900 have a gigabit Ethernet adapter, and the version you have is in fact the latest. There can be a lot of variables that can affect the network speed through the dock, and the first thing to double-check as you mention is that the unit is connected to a USB 3.0 port. Looking online at the specification to your laptop it appears all the USB ports are USB 3.0 so that should not be a factor here.

I know you mentioned that if you use the same Ethernet cable connected directly to your system the performance improves, but would you happen to have another Ethernet cable to swap in and test with? I have seen a few rare instances where this can help, and I just want to make sure the cable is not contributing to the behavior.

Can you also let me know what type of network device the dock is connecting to (router, switch) and the brand and model of said device?

Thank you,

Plugable Technologies

Bob - Thanks for the response. I tried swapping Ethernet cables, but that didn’t help. The download speed reduces by more than half when the Ethernet cable goes directly into the docking station before hooking up to my laptop via the USB cable. I actually have 2 of these docking stations, and the problem exist for both of them. Could it possibly be a problem with the cable that goes from the docking station to my laptop?

The router is a 2Wire 5268AC.

Hi Derek,

Thanks for getting back, appreciate you taking the time to swap the Ethernet cables and letting me know you encountered the same results with two docks (and for including the router model).

To your question, I typically would not expect the USB cable that connects the dock to your system to be the source of lower Ethernet speed but of course anything is possible. A quick way to help test the theory would be to swap the USB cable in use with the one from the ‘other’ docking station.

If that helps, great and we will know where to focus. If not, the next thing to check is that the connection speed is not being limited artificially. I have seen in some cases an instance where the network link speed is not negotiated properly. A way to help rule this out as the cause would be to manually set the link speed for the Ethernet Adapter in the dock to 1.0Gbps Full Duplex as described here -> http://support.displaylink.com/knowle…

Just let us know if swapping the USB cable or manually setting the link speed helps when you have a moment and we will go from there.

Thank you for your patience!


Bob - Thanks again for your response. I swapped out the cord and changed the setting to full duplex. Still didn’t change the issue (i.e., when I plug the Ethernet cord directly into the laptop I get around 450-500 mbs, but when I go through Plugable I only get 200-250 mps). thx

Hi Derek,

Thanks for getting back with the update. Our next step is to ensure that the DisplayLink driver for the dock (which includes the Ethernet component) is in a good state and not contributing to the problem by performing a ‘clean’ install of the latest version. If you would, please follow these steps:

  1. Disconnect the dock from the system and please remove the power cable from the dock so it turns off completely (this is important so the unit resets). Please keep it disconnected until the last step.
  2. Uninstall any and all ‘DisplayLink’ software that is present from within the Control Panel -> Programs and Features. Don’t worry if these entries are not present or if the process does not work, just move onto the next step
  3. Download, extract and run the DisplayLink cleaner tool, found here –> http://www.displaylink.com/downloads/… and ensure it displays “Cleaning Complete” when done (video walk-through if you need it -> https://youtu.be/AcVV1gD_FvI)
  4. Once the Cleaner has been run, reboot (even if not prompted to)
  5. Now download and install the 8.0 M2 DisplayLink software, found here –> http://www.displaylink.com/downloads/…
  6. Reattach the power cable to the dock first. Once the dock is powered on, reconnect it to your system which will trigger the final portion of the installation. If the device is not detected, please reboot the system.

Once complete, please also double-check that the 1.0 Gbps setting you changed recently is still set as intended and then test the behavior again.

Just let us know if that helps when you have a moment and we will go from there.

Thanks again for your patience!


Hi Derek,

We’re closing this thread due to inactivity, but if you have any updates or wish to resume troubleshooting please just email support@plugable.com (re: Ticket 156509) and we’ll be glad to revisit.