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

Regular Visitor

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

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.

Highlighted
Regular Visitor

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

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