U

Monday, July 31st, 2023 3:49 PM

Closed

2000+ Latency every 10-12 minutes after recent storms

We recently had some storms come through last week and knocked down a lot of trees and power. Once the outages were resolved, I started having intermittent latency issues. The issue occurs roughly every 10-12 minutes where I will go from 10-20ms to 2000+ms. This is causing issues with gaming / streaming / etc. The latency last about 5-10 seconds then clears. All equipment has been rebooted/bypassed/isolated. I can ping my modem gateway IP and the response times are normal (1ms). It only occurs when I ping anything outside of my network on the Xfinity network or beyond. This happens using a wired connection and wifi connection, it does not matter. I've used multiple computers as well.

This is a sample of it occurring:

9:47 PM
Reply from 1.1.1.1: bytes=32 time=1706ms TTL=54
Reply from 1.1.1.1: bytes=32 time=54ms TTL=54
Reply from 1.1.1.1: bytes=32 time=14ms TTL=54
Reply from 1.1.1.1: bytes=32 time=13ms TTL=54
Reply from 1.1.1.1: bytes=32 time=2167ms TTL=54

9:58 PM
Reply from 1.1.1.1: bytes=32 time=1918ms TTL=54
Reply from 1.1.1.1: bytes=32 time=34ms TTL=54
Reply from 1.1.1.1: bytes=32 time=15ms TTL=54
Reply from 1.1.1.1: bytes=32 time=16ms TTL=54
Reply from 1.1.1.1: bytes=32 time=2553ms TTL=54

10:09 PM
Reply from 1.1.1.1: bytes=32 time=2650ms TTL=54
Reply from 1.1.1.1: bytes=32 time=67ms TTL=54
Reply from 1.1.1.1: bytes=32 time=13ms TTL=54
Reply from 1.1.1.1: bytes=32 time=2581ms TTL=54

10:21 PM
Reply from 1.1.1.1: bytes=32 time=2471ms TTL=54
Reply from 1.1.1.1: bytes=32 time=56ms TTL=54
Reply from 1.1.1.1: bytes=32 time=2586ms TTL=54

10:32 PM
Reply from 1.1.1.1: bytes=32 time=2611ms TTL=54
Reply from 1.1.1.1: bytes=32 time=77ms TTL=54
Reply from 1.1.1.1: bytes=32 time=2586ms TTL=54

10:43 PM
Reply from 1.1.1.1: bytes=32 time=2175ms TTL=54
Reply from 1.1.1.1: bytes=32 time=58ms TTL=54
Reply from 1.1.1.1: bytes=32 time=12ms TTL=54
Reply from 1.1.1.1: bytes=32 time=1980ms TTL=54

7 Messages

2 years ago

I've narrowed it down to Channel 41 upstream. The channel is getting added every 11 minutes or so and when this happens, I get a latency spike. You can see the SNR on the channel is very bad and the channel eventually goes away after a minute or so probably due to low SNR power levels. I'd imagine this is an outside plant issue and not an inside home issue. I'm sure someone from comcast could actually check this for me and verify and get the correct tech out to fix the problem.

(edited)

7 Messages

2 years ago

What it looks like once channel 41 disappears. Also, I'm not getting my 100Mbit upload either, getting 65Mbit, which makes since because channel 41 is having issues.

Expert

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110.8K Messages

2 years ago

First. A modem can't display upstream channel SNR values. Those can only be read from their end at the CMTS. You must be referring to that channel's power level at 20.2 dB.

That said. FWIW, this is the very first time here that I've seen the usage of an OFDM channel on the upstream with Comcast. Looks like they are starting to roll it out now and it is likely to be experimental at this time and therefore has bugs. 

Keep in mind that I am NOT saying that this isn't the cause of the problem. What I am saying is that if you'll notice, that channel isn't actually locked in. When a channel is not locked in, the power level reading will not be accurate. Also, in the case of a downstream channel that is not actually locked in, not only will the power level reading be inaccurate, but so too will the SNR reading. Just sayin'.

(edited)

7 Messages

@EG​ I upgraded to 400x100 3 months ago but I had to use the Xfinity gateway they said as it was part of the package. I got an email July 20th saying that "SOON" I will no longer have to have XFi complete/Xfinity gateway in order to get these speeds. July 20th is also the day that storms rolled through. So I'm not sure if they changed something with the CMTS or if it is actually related to storm damage.

Keep in mind, I was uploading 100Mbit before the storm, now I am not. The OFDMA channel allows for much higher upload speeds so I would assume it's always been there and its not locking in because of low power reading (I do have a downstream OFDMA channel locked in). My modulation is also listed as QAM, which I'd imagine should be higher. Specs for upstream power from everything I've read should be 35+ and that 5th channel ranges between 20-27 for about 1 minute before disappearing. It also seems awfully close to the 4th upstream and would be an extremely narrow channel and overlapping. 

I'm sure someone from Xfinity DOCSIS Team or Plant team could quickly verify if there was an issue or not based on all the info I provided. Its just having someone do that. 
My latency spikes happen 100% when that 5th upstream pops in. Suppose it could even be the firmware of the gateway.

Expert

 • 

110.8K Messages

@user_a76899​ wrote;

Keep in mind, I was uploading 100Mbit before the storm, now I am not. The OFDMA channel allows for much higher upload speeds so I would assume it's always been there and its not locking in because of low power reading. 

As I stated, we have never seen an upstream OFDM channel posted here so far. And I know for a fact that they haven't yet offered it on the upstream perhaps until only very recently. How long have you been able to achieve 100 Mbps upload speed ? FWIW. There are other ways for them to provide 100 Mbps without having an OFDM channel. Here's some info on the "Mid-Split" method that they are indeed begun to upgrade their infrastructure to: https://www.cablelabs.com/blog/band-splits-splitting-our-way-to-10g 

My modulation is also listed as QAM, which I'd imagine should be higher.

Yes, it says QAM, but it doesn't list the number QAM that is being used so we don't the capacity that the individual channels can deliver. It is likely to be 64 QAM.

It also seems awfully close to the 4th upstream and would be an extremely narrow channel and overlapping. 

That may be an aberration due to the channel not being locked in. The other upstream QAM's are correctly spaced at 6 Mhz widths. OFDM carriers have very wide bandwidths ! I can't see them physically placing it starting at just 1 MHz above the next lower channel.

I'm sure someone from Xfinity DOCSIS Team or Plant team could quickly verify if there was an issue or not based on all the info I provided. Its just having someone do that. 

That won't likely happen here. Engineering staff do not post here.

My latency spikes happen 100% when that 5th upstream pops in. Suppose it could even be the firmware of the gateway.

It's likely to be that noise ingress in the upstream / return path somewhere is keeping the OFDM channel from locking in reliably. And as stated, it's likely to still be experimental and they still need to get the bugs ironed out of it and / or clean up the interference.

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7 Messages

I've been getting 100Mbit since I got the service 3 months ago. I've tested it multiple times throughout that period. 
I'm familiar with mid and high splits. 

I was assuming the QAM modulation would be listed since it is for the downstream channels (256 QAM), but that is just an assumption. I usually do not check my modem levels from the modem itself. I work for a cable provider and have always had access to the CMTS and other tools to view this information but this is not my job role so I'm no expert. 

Thanks for your feedback. I have a tech coming out tomorrow, hopefully they can provide some answers or escalate to a plant tech. 

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