Ethernet speed randomly cuts in half

[dennyhita]

Hello,

I have a pc connected directly to a ZyXEL VMG5313-B30A router with an ethernet cable. Normal internet speeds are 20mbps download and 2.5mbps upload.

Problem is, sometimes I get exactly half of that speed. No other devices are connected to the network. I usually unplug and then plug the cable back in, and that solves it, but not every time in first try.

How can I fix this?

Thank you

 

[anotherdrew]

Is the upload speed also cut in half? 10 mpbs is a standard Ethernet speed and I wonder if there is some noise or something on your Ethernet cable and so the hardware is cutting the speed to 10 mpbs (10base-T). Unplugging and replugging resets the connection allowing for faster speed until the hard detects the noise again and drops the speed again. If this is the case, then upload speed should be unaffected. The fix ... an issue like this is most likely the cable, but could also be one of the ports. Try a different cable first (Cat 6 preferably) and if that does not help, move the cable to a different port on the router. A bit of dust or lint in a port could also do this.

Let us know if that helps or if I am off track.

 

[dennyhita]

Is the upload speed also cut in half? 10 mpbs is a standard Ethernet speed and I wonder if there is some noise or something on your Ethernet cable and so the hardware is cutting the speed to 10 mpbs (10base-T). Unplugging and replugging resets the connection allowing for faster speed until the hard detects the noise again and drops the speed again. If this is the case, then upload speed should be unaffected. The fix ... an issue like this is most likely the cable, but could also be one of the ports. Try a different cable first (Cat 6 preferably) and if that does not help, move the cable to a different port on the router. A bit of dust or lint in a port could also do this.

Let us know if that helps or if I am off track.

Upload speed is unaffected.

I've spent the last 2 days testing other ports, but there doesnt seem to be any difference.
The cables are cat6. Only thing that might be causing this is that since I didnt have 1 cable long enough, I've connected 2 of them with an adapter, which is also cat 6. Total cable length is about 12m.

Is the adapter causing the problem?

 

[anotherdrew]

With everything you found out so far and knowing that the upload speed is unaffected, it seems very likely that there is a physical fault somewhere. It seems you've tested all the ports that are possible and cables, leaving the connector as one of the few thing that has been untested. I would be tempted to spend $10 to $15 on a new cable to find out.