Intermittent packet loss and high latencies

[Chris134]

I have been experience intermittent periods of high packet loss for a long time now.  It has become a major problem for me in the last few weeks as I need to use voice and video chat for work and I am frequently dropping from calls or people are telling me I am garbled or the can't hear me.

I have done extensive debugging of this issue:  I have experienced it with two different cable modems, while wired directly from the computer to the modem with no router, and using multiple coaxial and ethernet cables and multiple computers.  Using tracert, I can see that the issue occurs between me and the first hop and is not due to internet congestion.

Because the on-the-phone technicians have continued to believe that the problem is in my house (which I understand is reasonable because I'm sure it's true in must cases) over the last two days I have conducted an additional test: I went down into my basement with both cable modems, hooked them directly to the coaxial cable where it enters my house, and wired a laptop to the model via ethernet cable. I have included images and other information below documenting that the issue continues to occur with both modems in this setup, so I do not belive the problem is within my house.

On wednesday afternoon, I went down to the basement and hooked up the first of the two cable modems, which is a Netgear CM600. I ran a test using EMCO ping monitor to three destinations: comcast.com, 1.1.1.1 (CloudFlare DNS) and 8.8.8.8 (Google DNS). Here are the latencies I experience over a 20 minute period:

And here is the overall view showing packet loss to all destinations:

Using tracert, I can see that the issue occurs between me and the first destination. The problem predates the current coronavirus surge in usage. It comes in waves (sometimes the connection will be stable for a few hours, sometimes it is like this, and sometimes it is worse) and seems to happen more frequently during the day than at night.

The next morning, I brought the other cable model downstairs and ran the same test. It is an Arris SB8200. Here are the results:

I understand that low, stable latency can not be guaranteed to internet destinations at all times. However, daily extended periods of high packet loss and latencies bouncing from 20ms to 1000ms seems like a clear indicator of a problem, especially when tracert shows the issue comes between me and the first hop. The data here was not cherry-picked - this is just what was happening when I had a minute to record data, and sometimes it's even worse.

After the second test, I looked at the statistics on my modem, shown below. These mostly look fine to me, though I'm unsure what the high number of correcteds on channel 159 means.  Perhaps it's an indicator of the problem, though when I looked at the stats page for the other modem after that test, the SNR and power levels also looked fine and there were no correcteds or uncorrectables.   I am happy to run again with the first modem and capture these stats if helpful.

I would appreciate it if someone from Comcast could work with me to debug this issue, as it is substatially disrupting my ability to work from home and to use the internet for other purposes. I have of course tried resetting the modems and followed the other steps on the debugging page many times. I think the fact that the issue occurs with multiple cable modems when wired directly to the place where cable enters my house is an indication that the problem is not with my equipment, but I am happy to work with Comcast to debug in whatever way seems best.

Thanks!

[Chris134]

Since the images are not showing up for some reason, here is an imgur album with all of them:

https://imgur.com/a/AopCccE

[Chris134]

Hi,

I'd really appreciate it if I could get help with this issue. Thanks!

[Chris134]

Hi,

Could someone please assist me with this?  The problem is continuing to occur.

Thanks!

[Chris134]

Hello,

I notice that the upstream power levels on the modem debug page shown above are well below the range that the Arris documentation claims is supported. According to the Arris documentation for the SB8200, I should see upstream power levels of 45 to 51 dBmV.

Could this be the cause of the issue I am seeing? I believe upstream power levels are controlled by Comcast, so it could explain why the issue occurs with both cable modems.  According to the Comcast website, this cable modem is supported so I imagine I should see upstream power levels within the supported range, but I am not an expert.

Could someone from Comcast help me with this?  Thanks.

[Chris134]

Hello,

This issue is still present today.  It makes voice/video chat nearly unusable for extended periods, which is making it very difficult for me to work from home.  The issue seems to be more frequent during weekdays than at night or during the weekend (at least, I think so).

Could someone from Comcast help me debug this issue?  Thank you.

[ni82156]

Good luck Chris. Same issue here have had 2 techs come out been chatting them everyday which they've now disabled and I'm still calling. I've replaced my modem, my router, all coax lines, the coax line from the pole to the house and they just keep wanting to send another tech out. I've said over and over again another tech is going to do what exactly?  The issue does not reside on my network there is an issue with the route. I am having 0 success getting through to anyone who can give me a straight answer or seem like they want to fix the issue. 

[pcross616]

Like everyone on this thread I too am having issues.  I have pinned mine down to a downstream issue.  I have about 20% packet loss which making working from home using Zoom or any real telecommiunication program useless.  I have been looking for support from Comast multipul times I called and have not had any luck so let me share what I have done so you all can maybe get more information as well.

I have a very well monitor setup so everything I am posting is direct on the gateway and is NOT traversing my NAT or my firewall.

This is 1hr worth of traffic with packet loss about 20% (That dead spot is me getting told by comcast to reboot my modem).  As you can see it returns to the same rate.

(img link- https://i.imgur.com/fDeMDck.png)

Using iperf3 and public servers I confirmed that my downstream is where my loss happens.

You can get iperf here (https://iperf.fr/)

I am again running this on the edge on my router (no nat, WAN ip). I am using UDP to remove any ACKs and other TCP over head.  By using '-R' I am having the remote server send the UDP traffic if you wanted to test upstream remove the '-R'.   All my upstream tests had no packet loss.

iperf3 -c iperf.he.net -u -p 5201 --get-server-output -b 30M -R

Connecting to host iperf.he.net, port 5201
Reverse mode, remote host iperf.he.net is sending
[  5] local 73.53.XX.XXX port 6995 connected to 216.218.207.42 port 5201
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-1.00   sec  3.40 MBytes  28.5 Mbits/sec  0.009 ms  134/2575 (5.2%)
[  5]   1.00-2.00   sec  3.40 MBytes  28.5 Mbits/sec  0.011 ms  34/2477 (1.4%)
[  5]   2.00-3.00   sec  3.62 MBytes  30.4 Mbits/sec  0.011 ms  60/2660 (2.3%)
[  5]   3.00-4.00   sec  3.54 MBytes  29.7 Mbits/sec  0.010 ms  29/2568 (1.1%)
[  5]   4.00-5.00   sec  3.45 MBytes  28.9 Mbits/sec  0.007 ms  92/2569 (3.6%)
[  5]   5.00-6.00   sec  3.53 MBytes  29.6 Mbits/sec  0.010 ms  30/2565 (1.2%)
[  5]   6.00-7.00   sec  3.35 MBytes  28.1 Mbits/sec  0.008 ms  100/2507 (4%)
[  5]   7.00-8.00   sec  3.49 MBytes  29.3 Mbits/sec  0.006 ms  126/2633 (4.8%)
[  5]   8.00-9.00   sec  3.51 MBytes  29.5 Mbits/sec  0.026 ms  47/2569 (1.8%)
[  5]   9.00-10.00  sec  3.47 MBytes  29.1 Mbits/sec  0.011 ms  27/2517 (1.1%)
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.00  sec  35.8 MBytes  30.0 Mbits/sec  0.000 ms  0/25640 (0%)  sender
[  5]   0.00-10.00  sec  34.8 MBytes  29.2 Mbits/sec  0.011 ms  679/25640 (2.6%)  receiver
Server output:
Accepted connection from 73.53.XX.XXXX, port 24746
[  5] local 216.218.207.42 port 5201 connected to 73.53.XX.XXX port 6995
[ ID] Interval           Transfer     Bandwidth       Total Datagrams
[  5]   0.00-1.00   sec  3.23 MBytes  27.1 Mbits/sec  2318
[  5]   1.00-2.00   sec  3.58 MBytes  30.0 Mbits/sec  2568
[  5]   2.00-3.00   sec  3.58 MBytes  30.0 Mbits/sec  2569
[  5]   3.00-4.00   sec  3.58 MBytes  30.0 Mbits/sec  2568
[  5]   4.00-5.00   sec  3.58 MBytes  30.0 Mbits/sec  2569
[  5]   5.00-6.00   sec  3.58 MBytes  30.0 Mbits/sec  2568
[  5]   6.00-7.00   sec  3.58 MBytes  30.0 Mbits/sec  2569
[  5]   7.00-8.00   sec  3.58 MBytes  30.0 Mbits/sec  2568
[  5]   8.00-9.00   sec  3.58 MBytes  30.0 Mbits/sec  2569
[  5]   9.00-10.00  sec  3.58 MBytes  30.0 Mbits/sec  2568
[  5]  10.00-10.04  sec   366 KBytes  73.1 Mbits/sec  257
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
[  5]   0.00-10.04  sec  35.8 MBytes  29.9 Mbits/sec  0.000 ms  0/25691 (0%)

I then decided to verify my cable modem status page.  I did notice 1 of my channels was at 33.2 (comcast recommends 35 as a min).  So is it odd just that one channel is low?  I have checked all my fittings and they are tight and have compression crimps.   I even changed the cable and routing just to see if there was someting with the wires in the house.  It didnt change.  I still have the same splitter in the line so that would be the next thing to replace.  But would that really equal this much packet loss (20%) ???

 (img link- https://i.imgur.com/IzMbMnD.png)

In the end I am getting no where with the automated tech support modem reboot circles and tier 1 help and really could use help from a technical contact from comcast.  I am willing to do pretty much anything at this point.   (As I feel many of us are..).  

Thanks and keep the idea flowing.

This post was helpful to me: https://forums.xfinity.com/t5/Your-Home-Network/Packet-Loss-and-Latency-Spikes-Online-Chat-and-Games...

And this community post:

https://forums.xfinity.com/t5/Internet/ANSWERED-Tips-for-troubleshooting-your-Xfinity-Internet/ta-p/...

[Chris134]

Hello,

The issue is still present and disrupting my ability to work from home today.  Could someone from Comcast help me with this issue?  Thank you.

[Chris134]

Hello, I am still experiencing frequent packet loss that is disrupting my ability to work from home.  Could someone from Comcast give me a hand?  Thanks.

[pcross616]

Just wanted to follow-up.  I spent a good 1 and a half with a tech from the CDO.  He and I did remote diganostics.  I knew I had noise on the line but nothing I did seemded to help.  Turns out it was my cable box.  I replaced my spiltter and my compression fittings check all my face place connetors.  In the end I just disconnected everything from my splitter other than my cable modem.  Ran the line noise checks and my iperf command above.  No packet loss... slowy I added more connections segment by segment.  Not until I turned my cable box back on I had nosie on the line.

Unforunantly, it is hard to know if there is noise on the line without talking to a tech and them running a check on the line.  But you can get a hint based on the status page of your modem. (192.168.100.1 or 10.0.0.1).  Watch the power levels and dB change based on what is plugged in and run a trhoughput test via iperf.  I had a low level FM noise showing up on the line.  If you call comcasat ask to get a line noise check they may need to redirect you to a different operation tech but push for that and they can help you troubleshoot without stepping in your house.  Now if its outside they will send a tech but its not easy now a days.

Down to about 1-2% packetloss over an 1hour when my cable box is not plugged in (pretty normal for a cable modem).   Now I need a new cable box from them. 🙂

[Chris134]

Hi,

Thanks for the reply.  I've been monitoring my cable modem stats and they seem normal, but I'll look into some of the other diagnostics you mentioned.

I would appreciate it if someone from Comcast could also reply and assist me with this issue directly.  I am still having daily intermittent periods of substantial packet loss and extreme variation in latency.  Thanks!

[Chris134]

Hello,

I am still experiencing intermittent periods of high packet loss and highly variable latency every day, originating between me and the first hop.  As documented above, I have done extensive testing and can not find any issues with the equipment in my house.  Could someone from Comcast please help me with this?  Thanks.