Frequent packet loss, disconnects with CM1200 modem and 600Mb Plan

[kickaha]

Hello! I've been experiencing connectivity issues and packet loss with my Internet service for quite some time. The severity of the problem varies substantially from hour to hour, ranging from rock-solid through various degrees of packet loss and all the way to hour-long connection failures. Interestingly, even when packet loss is occurring, uncorrectable codewords are not reported.

I recently updated my Comcast package to a new plan with a higher speed tier (600Mb vs. 250Mb). The problem began shortly thereafter; my connection had previously been quite good.

Here is the current channel data from my modem:

Downstream Bonded Channels

Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables 1 Locked QAM256 29 639000000 Hz 4.2 dBmV 39.6 dB 1 0 2 Locked QAM256 1 459000000 Hz 4.6 dBmV 40.9 dB 0 0 3 Locked QAM256 2 465000000 Hz 4.7 dBmV 40.8 dB 0 0 4 Locked QAM256 3 471000000 Hz 4.8 dBmV 40.9 dB 0 0 5 Locked QAM256 4 477000000 Hz 5 dBmV 41 dB 0 0 6 Locked QAM256 5 483000000 Hz 5 dBmV 40.9 dB 0 0 7 Locked QAM256 6 489000000 Hz 4.8 dBmV 40.8 dB 0 0 8 Locked QAM256 7 495000000 Hz 4.7 dBmV 40.7 dB 0 0 9 Locked QAM256 8 507000000 Hz 4.9 dBmV 40.7 dB 0 0 10 Locked QAM256 9 513000000 Hz 5 dBmV 40.7 dB 0 0 11 Locked QAM256 10 519000000 Hz 4.9 dBmV 40.7 dB 0 0 12 Locked QAM256 11 525000000 Hz 4.7 dBmV 40.5 dB 0 0 13 Locked QAM256 12 531000000 Hz 4.6 dBmV 40.4 dB 0 0 14 Locked QAM256 13 543000000 Hz 4.3 dBmV 40.2 dB 0 0 15 Locked QAM256 14 549000000 Hz 4.4 dBmV 40.3 dB 0 0 16 Locked QAM256 15 555000000 Hz 4.4 dBmV 40.1 dB 0 0 17 Locked QAM256 16 561000000 Hz 4.3 dBmV 40.1 dB 0 0 18 Locked QAM256 17 567000000 Hz 4 dBmV 40 dB 0 0 19 Locked QAM256 18 573000000 Hz 3.9 dBmV 40 dB 0 0 20 Locked QAM256 19 579000000 Hz 3.9 dBmV 40 dB 0 0 21 Locked QAM256 20 585000000 Hz 4.3 dBmV 40 dB 0 0 22 Locked QAM256 21 591000000 Hz 4.3 dBmV 40 dB 0 0 23 Locked QAM256 22 597000000 Hz 4.4 dBmV 40 dB 0 0 24 Locked QAM256 23 603000000 Hz 4.3 dBmV 39.9 dB 1 0 25 Locked QAM256 24 609000000 Hz 4 dBmV 39.7 dB 0 0 26 Locked QAM256 25 615000000 Hz 4.1 dBmV 39.7 dB 1 0 27 Locked QAM256 26 621000000 Hz 4.5 dBmV 39.7 dB 1 0 28 Locked QAM256 27 627000000 Hz 4.6 dBmV 39.6 dB 2 0 29 Locked QAM256 28 633000000 Hz 4.3 dBmV 39.5 dB 0 0 30 Locked QAM256 30 645000000 Hz 4.2 dBmV 39.6 dB 1 0 31 Locked QAM256 31 651000000 Hz 4.6 dBmV 39.8 dB 2 0 32 Locked QAM256 32 657000000 Hz 4.6 dBmV 39.8 dB 0 0

Upstream Bonded Channels

Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power 1 Locked ATDMA 1 5120 Ksym/sec 17300000 Hz 44 dBmV 2 Locked ATDMA 2 5120 Ksym/sec 23700000 Hz 45 dBmV 3 Locked ATDMA 3 5120 Ksym/sec 30100000 Hz 46 dBmV 4 Locked ATDMA 4 5120 Ksym/sec 36500000 Hz 45.5 dBmV 5 Locked ATDMA 5 1280 Ksym/sec 41200000 Hz 48 dBmV 6 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV 7 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV 8 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV

Downstream OFDM Channels

Channel Lock Status Modulation / Profile ID Channel ID Frequency Power SNR / MER Active Subcarrier Number Range Unerrored Codewords Correctable Codewords Uncorrectable Codewords 1 Locked 0 159 722000000 Hz 7.5 dBmV 40.5 dB 1126 ~ 2969 77616108 29 0 2 Not Locked 0 0 0 Hz 0 dBmV 0.0 dB 0 ~ 4095 0 0 0

Upstream OFDMA Channels

Channel Lock Status Modulation / Profile ID Channel ID Frequency Power 1 Not Locked 0 0 0 Hz 0 dBmV 2 Not Locked 0 0 0 Hz 0 dBmV

Extended Upstream Transmit Power

Enable Extended Upstream Transmit Power (checked, greyed out)

Here is a sample event log from a rough patch, showing a pattern of dynamic range window violations:

Time	Priority	Description
Mon Jul 13 19:50:48 2020	Critical (3)	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:57:57 2020	Warning (5)	Dynamic Range Window violation
Mon Jul 13 17:57:57 2020	Warning (5)	RNG-RSP CCAP Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:57:37 2020	Warning (5)	Dynamic Range Window violation
Mon Jul 13 17:57:37 2020	Warning (5)	RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:57:20 2020	Critical (3)	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:57:18 2020	Warning (5)	Dynamic Range Window violation
Mon Jul 13 17:57:17 2020	Warning (5)	RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:56:49 2020	Critical (3)	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:56:18 2020	Warning (5)	Dynamic Range Window violation
Mon Jul 13 17:56:18 2020	Warning (5)	RNG-RSP CCAP Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:56:18 2020	Warning (5)	Dynamic Range Window violation
Mon Jul 13 17:56:18 2020	Warning (5)	RNG-RSP CCAP Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;
Mon Jul 13 17:56:18 2020	Warning (5)	Dynamic Range Window violation
Mon Jul 13 17:56:18 2020	Warning (5)	RNG-RSP CCAP Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW;CM-MAC=XX:XX:XX:XX:XX:XX;CMTS-MAC=XX:XX:XX:XX:XX:XX;CM-QOS=1.1;CM-VER=3.1;

And here are the troubleshooting steps I've already tried:

• Resetting the modem.
• First and second level tech support, which included resetting and reprovisioning the modem, hooking a PC directly to the modem to bypass internal equipment, etc.
• Trying a Comcast-supplied replacement modem.
• Replacing the wall-to-modem coax cable with a Comcast-supplied cable. (There are no splitters on the interior side of the wallplate; I don't know the details of how this house was originally wired for cable.)
• Inspecting the wallplate (including the connection on the back side). No apparent problems there.
• Run Net Uptime Monitor and other connectivity checkers over several weeks to verify that the problem doesn't seem to correlate with anything I'm doing at the time (it occurs even when I'm not here, for example) and that the house wired and wireless networks are sound (I've never seen packet loss on connections among my local devices; and when the problem occurs, it affects all wired and wireless devices in the house simultaneously).

Any other things I should try short of "have Comcast roll a truck and check the exterior connection"? Thanks in advance for any advice.

[kickaha · Accepted solution]

Comcast tech support has now booked a tech visit to check the outside wiring, so let's call this one solved.