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I noticed very bad latency (ping times) when playing Rocket League on my PC connected to the internet over PLC (power-line communication, i.e. ethernet over power) -- 60 ms when my gaming PC is the only one sucking data and around 120 ms with other clients. Using the command line to ping 8.8.8.8 for testing purposes gives me a 24 ms ping and even pinging the EU Rocket League servers directly gives me no more than 40 ms of ping.

I had the idea to try different packet sizes, and I was dead-on with that guess. Pinging my own router over PLC gives a RTT of 3 ms if the packet's size is 975 bytes, but a RTT of 22 ms if the packet's size is 976 bytes.

Both packet sizes have a RTT of around 0.5 ms when I connect to the router directly using an ethernet cable, which makes me think it's not an issue with the router but the PLC.

As this seemed to map exactly onto the concept of MTU (maximum transmission unit), I tried setting the MTU on my PC to higher and lower values than the default 1500 using the command sudo ifconfig enp3s0 mtu 1500. Sadly, no improvement in Rocket League ping. It also seems to NOT be possible to set the MTU of my router manually. I also downloaded TP-Link's settings utility for the adapters (tpPLC) and couldn't find an MTU setting there either.

Technical information:

  • device connecting router to power line: TP-Link TL-PA4020P
  • devices connecting power line to PCs: TP-Link TL-WPA4220
  • "gaming" PC running Linux Mint 18.3 and Windows (high latency occurs on both)
  • residential gateway device: Fritz!Box 7490 (did a factory reset today so it's all default settings)
  • as is clear from the Fritz!Box, I'm in Germany (mains electricity varies between countries)

How can I eliminate the 19 ms penalty when sending a "large" packet over PLC? Additionally, should I worry about the Rocket League servers (for small packets) having worse ping than 8.8.8.8?

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  • I don't have enough for an answer, but I'd investigate buffer bloat – Tetsujin Oct 4 '18 at 6:37
  • Buffer bloat would be relevant for the multiple clients part, but not the PLC part, which is my main problem, right? – xjcl Oct 4 '18 at 13:45
  • Note that the emulated Ethernet MTU might not necessarily correspond to the Homeplug/PLC connection's MTU. – user1686 Oct 4 '18 at 13:53
  • Yeah. But I downloaded TP-Link's settings utility for the adapters (tpPLC) and couldn't find an MTU setting. Let me add that to the question. – xjcl Oct 4 '18 at 13:59

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