Ping skyrockets + Packet Loss when Uploading
 

I'm posting this on behalf of a friend who I've been having a nightmare playing online games with recently because of his Virgin Media connection.

Essentially, whenever he's doing an upload his ping spikes up massively, and he gets packet loss. These uploads are capped at 1MB/s so aren't maxing-out his bandwidth (in speedtests he gets 12Mbps upload).

See BQM:
https://www.cableforum.uk/images/local/2020/07/8.png

You can see at 6pm he has some uploads running and the average pings spike up to the 160ms range. More worryingly, you can see some red packet loss.

I asked him to show me the Downstream and Upstream pages on the router.
Note, the "Pre RS Errors" and "Post RS Errors" were after about an hour from last rebooting the router.

Downstream:
https://www.cableforum.uk/images/local/2020/07/9.png

Upstream:
https://www.cableforum.uk/images/local/2020/07/10.png

Any idea what the cause of this issue might be? Is this the famous bufferbloat issue on underpowered routers?

Re: Ping skyrockets + Packet Loss when Uploading
 

1MB/s = 8Mbit + overheads, so it doesn't surprise me his ping skyrockets when he's uploading files, if his max upload speed is 12mbit.

But that doesn't sound right, either. What's his actual Virgin package and what's his modem provisioned to? If he's on 100Mb, his max upload is actually 10mbit, not 12. If he's on 200, it should be 20, 350 should be 35. Something doesn't check out.

Re: Ping skyrockets + Packet Loss when Uploading
 

Presumably the 10M upload is over provisioned, so may read as up to 12 on a speed test.

However, it doesnt matter, uploading at you max speed is going to kill pings, regardless of what that max is.

Re: Ping skyrockets + Packet Loss when Uploading
 

The rule of thumb I'd read is you should cap uploads to 80% of your upload speed, so I just suggested he do a speedtest (which was 12Mbps), then 80% is 9.6Mbps, which was reduced to 8Mbps for some leeway. I will suggest he reduces this even more.

I understand maxing out your download/upload will affect pings, but it surely shouldn't cause packet loss?

This is my home connection (VM 200Mbps), I run PC backups which take a few days to complete. There is no upload bandwidth limit imposed, meaning it saturates my upload bandwidth.
My BQM chart shows rises in ping, but not to the same extreme, and there is no packet loss (my backup finished at 2pm here):
https://www.cableforum.uk/images/local/2020/07/11.png

Compare this to my friend's BQM chart, even with a bandwidth limit imposed there are much higher average pings and even some packet loss.

https://www.cableforum.uk/images/local/2020/07/8.png
Are the number of "Post RS Errors" on Downstream Channels 1-4 (but not 5-8) normal on my friend's router?

Re: Ping skyrockets + Packet Loss when Uploading
 

no, you shouldnt be getting the T3 timeouts on the upstream either. Click on reset counters on the post-rs errors and reboot the shub and see what happens.

Re: Ping skyrockets + Packet Loss when Uploading
 

These screenshots were taken about an hour after rebooting the shub, which I believe resets these numbers. But I will continue to monitor it.

What causes these timeouts? The power levels look in-spec (upstream power looks of 48-49 is borderline from what I've read) and SNR looks about right too.

Re: Ping skyrockets + Packet Loss when Uploading
 

48 is mint and mine has been 48 since the dawn of time. There can be several different types of problems with upstream channels which is why there are the 4 different T levels and depending on what the problem is it can impact the downstream and make it looks like there is a downstream fault when there isnt one.

Re: Ping skyrockets + Packet Loss when Uploading
 

This graph shows my system (170Gb) being backed up to Acronis Cloud between about 02:30 and 04:00 last Sunday morning. (uncapped upload) Upload speed for this backup tends to be in the range 30-45 Mbps out of the over-provisioned 50Mbps I pay for. This is the kind graph profile I would expect from a decently performing connection. I would agree that the graph in the OP isn't satisfactory.

https://www.cableforum.uk/images/local/2020/07/12.png

Re: Ping skyrockets + Packet Loss when Uploading
 

Are you and your friend both using the same Hub?
Are you both using the hub in hub mode, or router or what?
If so, do you have the same router?

Is your friend actually experiencing packet loss? The TBB graph is only showing that the ping request didn't get a response, this can happen with some setups when the connection is being throttled, as IPMC responses are fairly low in the priority.

Re: Ping skyrockets + Packet Loss when Uploading
 

No, we live at different houses, but are just playing video games on the internet together.

Both hubs are in router mode, I have the SH3 and my friend (with the connection problems) has the SH2ac.

Interesting theory about the IPMC responses.

Re: Ping skyrockets + Packet Loss when Uploading
 

ICMP

Re: Ping skyrockets + Packet Loss when Uploading
 

Its not a theory.

Routers treat ICMP (pings) as low priority, so when they get busy, they can end up just ignoring/dropping them.

Re: Ping skyrockets + Packet Loss when Uploading
 

theory = explanation