Periodical Powerline LAN Performance Spikes

Question

I have some problems with my powerline LAN: The network works perfectly fine 80% of the time, but 20% of the time it is really slow. E.g. if PC1, PC2 and PC3 are playing an online game the ping drops from 50 ms to 200 ms once or twice per hour. These performance spikes only last a few minutes and after that, everything goes back to normal again.

Network Overview:

PC1|Adapter1|\                                     
PC2|Adapter2|-> (powerline) -> |Adapter4| -> |Router| -> Modem -> Internet
PC3|Adapter3|/                                \- PC4 (UPS, lots of devices), PC5

Some random facts about the network:

• Even if PC2 and PC3 are offline the lag issue still remains
• The network worked perfectly before the USP and PC5 were added¹
• I recently changed the adapter on PC1 and the frequency of lag issues decreased
• Sometimes PC3 can't connect to the network at all
• Adapter4 is not connected to the UPS
• PC5 is used a server and does backups for all the other computers

What could cause this issues?

• The UPS that was recently added?
• The increased number of devices connected to the power outlet on PC4?
• A broken network card?
• A broken powerline LAN adapter?

I can do some tests with the network, but the amount of the time where PC4, PC5 or the UPS can be disconnected from the network or switched off is very limited.

¹: I am not really sure about this one. I don't play online games so frequently that I can pinpoint it to that exact date.

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Answers to comments on this question:

My bet is that it's just network load. It could be two PCs talking to each other, saturating the powerline. It could be one PC saturating the Internet link

I can somehow exclude the powerline saturation issue, because I had a case where only PC1 and PC4 (PC4 is not connected to the powerline network) were online and the lag issue was still there.

Regarding the Internet link saturation: What I think is odd is that it happens periodically and only for a short time. I would understand a relation between heavy Internet usage (downloads, streaming, etc.) and performance problems for the other clients, but the problems would be long and random in this case.

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Update:

Did some testing yesterday: When PC4 is online, the lag issues start. Normal web browsing on PC4 causes periodic performance issues on all other clients.

Answer 1

Turned out the router was causing the problem. I don't know what the issue was, but as soon as the old router was replaced everything was working fine, and all network problems were solved.

Answer 2

According to your update, it might be a faulty network card on PC4.

Try replacing the card, or switching cards between computers.

Answer 3

Now that you have narrowed it down to one PC (sortof), two iterations of "bisectination" are complete. (I say sortof, because it could just be PC4's location or external components, not the PC itself)

• dump the UPS on that box (just because it is fast and easy) - fixed? - remove/replace UPS
• use a different PC in PC4's place using all of its cables (same lan adapter, UPS, cables etc... that PC4 was using) - fixed? - must be in PC4 (lan card or its driver or internal interference from some other component)
• if replacing PC4 did not fix it, it could be lan adapter or "interconnecting wiring" - try using a different lan adapter and/or swapping out your lan cables (bad ethernet cables are a fairly common problem and could have been damaged while you were shifting stuff around to put in your shiny new UPS)
• if none of that works try a different outlet (a long extension cord will work temporarily), something on that circuit could be causing interference

Answer 4

Ethernet over Powerline is notoriously sensitive to noise in the power line that doesn't bother any power devices. One place I lived, every time the refrigerator compressor turned on to cool the refrigerator the EoP pretty much stopped working. Now in that case it was near its limits to begin with, but it wouldn't surprise me if you had something similar. Any electric motor (refrigerator, dishwasher, clothes washer, blower for central heat, etc.) can cause serious degradation of the network and there's not much you can do about it.

What kind of UPS do you have? Where do you have power filtering (e.g. surge suppression)? One thing to note is that if a surge suppressor is plugged into the same outlet (or even the same circuit but a different outlet nearby) as the EoP adapter it can degrade network performance. So you may have lowered your safety margin by recently plugging in a new surge supressor and now suffering from refrigerator noise where you didn't used to.

I'd start by making sure that at the very least you don't have the UPS or any surge protectors plugged in within 6 feet of an EoP adapter.