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Wednesday, January 22nd, 2025 1:37 AM

Frequent packet loss and intermittent lags - looking for answers

Been at this house for 9 years with consistent service, but some terrible packet loss has cropped up in the last month. Frequent lags in any video game (every 2-3 minutes) and occasionally will briefly cut out on video calls while working. (tested hard wired direct to modem, issue persists on 3 different PCs)

I've had a technician visit twice in the last week. The first tech claimed there was no issue with the signal coming to my home, but poor signal on the cable from the box on the outer wall to the splitter inside. He replaced the splitter with a MoCA filter (I don't have cable TV and have never needed one here before), told me my signal looked good and left. Issues did not change so I scheduled a follow-up visit noting the issue had not been resolved. Because I rescheduled, they sent another tech (may have been a supervisor) who said the MoCA filter made no difference, but did not see signal issues anywhere. Strong signal all the way up to the modem. Because of this he told me there was nothing they could do, and to try replacing my modem. 

I replaced my 2 year old Netgear CM2000 with a CM3000 today, running through Xfinity's internet trouble shooting guide both before and after the purchase and set-up of the new modem. Unfortunately the new modem has made no difference. There has got to be noise ingress somewhere. I live in a group of townhomes with a lot of units sharing pedestals, it feels difficult to pinpoint where there is noise or getting Xfinity to take a serious look at where it is coming from. The issue being intermittent makes it difficult to test, open to suggestions! I am willing to work with Xfinity and pay to replace wiring in my home if necessary, but need them to meet me halfway and stop dismissing the issues with my service.

Some errors I get from the Event log on both the old and new modem:

Started Unicast Maintenance Ranging - No Response received - T3 time-out

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing

RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW

Based on the Xfinity trouble-shooting guide, some of the ranging errors can be normal but I don't know how often is normal. Viewing the export from the modem, the signal looks good and matches the specs Xfinity provides in the guide. No correctables/uncorrectables that I see, but not sure how to catch that "in the act" so to speak. Thank you in advance for any help!

Netgear CM3000

Downstream Bonded Channels

Channel

Lock Status

Modulation

Channel ID

Frequency

Power

SNR

Correctables

Uncorrectables

1

Locked

QAM256

4

393000000 Hz

1.5 dBmV

41.0 dB

0

0

2

Locked

QAM256

1

375000000 Hz

2.1 dBmV

41.2 dB

0

0

3

Locked

QAM256

2

381000000 Hz

2.5 dBmV

41.3 dB

0

0

4

Locked

QAM256

3

387000000 Hz

2.1 dBmV

41.2 dB

0

0

5

Locked

QAM256

5

399000000 Hz

1.0 dBmV

40.8 dB

0

0

6

Locked

QAM256

6

405000000 Hz

0.3 dBmV

40.5 dB

0

0

7

Locked

QAM256

7

411000000 Hz

0.5 dBmV

40.5 dB

0

0

8

Locked

QAM256

8

417000000 Hz

0.1 dBmV

40.3 dB

0

0

9

Locked

QAM256

9

423000000 Hz

0.1 dBmV

40.3 dB

0

0

10

Locked

QAM256

10

435000000 Hz

0.8 dBmV

40.6 dB

0

0

11

Locked

QAM256

11

441000000 Hz

0.6 dBmV

40.6 dB

0

0

12

Locked

QAM256

12

453000000 Hz

1.3 dBmV

40.9 dB

0

0

13

Locked

QAM256

13

459000000 Hz

1.2 dBmV

40.7 dB

0

0

14

Locked

QAM256

14

465000000 Hz

1.4 dBmV

40.7 dB

0

0

15

Locked

QAM256

15

471000000 Hz

1.3 dBmV

40.7 dB

0

0

16

Locked

QAM256

16

477000000 Hz

1.5 dBmV

40.8 dB

0

0

17

Locked

QAM256

17

483000000 Hz

2.0 dBmV

40.9 dB

0

0

18

Locked

QAM256

18

489000000 Hz

2.1 dBmV

40.9 dB

0

0

19

Locked

QAM256

19

495000000 Hz

2.1 dBmV

41.0 dB

0

0

20

Locked

QAM256

20

501000000 Hz

1.7 dBmV

40.9 dB

0

0

21

Locked

QAM256

21

507000000 Hz

2.0 dBmV

41.0 dB

0

0

22

Locked

QAM256

22

513000000 Hz

2.4 dBmV

41.2 dB

0

0

23

Locked

QAM256

23

519000000 Hz

2.3 dBmV

41.1 dB

0

0

24

Locked

QAM256

24

525000000 Hz

2.3 dBmV

41.1 dB

0

0

25

Locked

QAM256

25

531000000 Hz

1.8 dBmV

41.0 dB

0

0

26

Locked

QAM256

26

537000000 Hz

3.0 dBmV

41.3 dB

0

0

27

Locked

QAM256

27

543000000 Hz

3.1 dBmV

41.3 dB

0

0

28

Locked

QAM256

28

549000000 Hz

2.4 dBmV

41.1 dB

0

0

29

Locked

QAM256

29

555000000 Hz

2.1 dBmV

41.0 dB

0

0

30

Locked

QAM256

30

561000000 Hz

3.1 dBmV

41.3 dB

0

0

31

Locked

QAM256

31

567000000 Hz

3.2 dBmV

41.4 dB

0

0

32

Locked

QAM256

32

573000000 Hz

2.8 dBmV

41.3 dB

0

0

 

Upstream Bonded Channels

Channel

Lock Status

US Channel Type

Channel ID

Symbol Rate

Frequency

Power

1

Locked

ATDMA

6

2560 Ksym/sec

10400000 Hz

39.0 dBmV

2

Locked

ATDMA

2

5120 Ksym/sec

22800000 Hz

36.0 dBmV

3

Locked

ATDMA

3

5120 Ksym/sec

29200000 Hz

36.0 dBmV

4

Locked

ATDMA

4

5120 Ksym/sec

35600000 Hz

36.0 dBmV

5

Locked

ATDMA

5

2560 Ksym/sec

40400000 Hz

33.5 dBmV

6

Locked

ATDMA

1

5120 Ksym/sec

16400000 Hz

37.0 dBmV

7

Not Locked

Unknown

0

0

0

0.0 dBmV

8

Not Locked

Unknown

0

0

0

0.0 dBmV

 

Downstream OFDM Channels

Channel

Lock Status

Profile ID

Channel ID

Frequency

Power

SNR / MER

Active Subcarrier
Number Range

Unerrored
Codewords

Correctable
Codewords

Uncorrectable
Codewords

1

Locked

0 ,1 ,2 ,3

193

690000000 Hz

1.38 dBmV

40.6 dB

1108 ~ 2987

445484276

414412226

0

2

Not Locked

0

0

0 Hz

0 dBmV

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

 

 

Event Log from setup of new CM3000 today

Time

Priority

Description

Tue Jan 21 19:12:46 2025

(Critical (3))

Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:21:51 2025

(Warning (5))

Dynamic Range Window violation

Tue Jan 21 12:21:51 2025

(Warning (5))

RNG-RSP CCAP Commanded Power Exceeds Value Corresponding to the Top of the DRW;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:21:46 2025

(Critical (3))

Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:21:30 2025

(Notice (6))

DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:21:25 2025

(Notice (6))

TLV-11 - unrecognized OID;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Time Not Established

(Notice (6))

Honoring MDD; IP provisioning mode = IPv6

Time Not Established

(Critical (3))

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:20:13 2025

(Critical (3))

Resetting the cable modem due to docsDevResetNow

Tue Jan 21 12:19:33 2025

(Critical (3))

Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:15:53 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Time Not Established

(Critical (3))

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:14:08 2025

(Critical (3))

Resetting the cable modem due to docsDevResetNow

Tue Jan 21 12:14:06 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 12:03:12 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Time Not Established

(Critical (3))

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:55:17 2025

(Critical (3))

Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:50:31 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:50:09 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Time Not Established

(Critical (3))

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:47:56 2025

(Critical (3))

Resetting the cable modem due to docsDevResetNow

Tue Jan 21 11:45:11 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:44:29 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Time Not Established

(Critical (3))

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:41:30 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:40:59 2025

(Critical (3))

No Ranging Response received - T3 time-out;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Tue Jan 21 11:40:07 2025

(Critical (3))

SYNC Timing Synchronization failure - Loss of Sync;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Time Not Established

(Critical (3))

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

Time Not Established

(Critical (3))

SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=(Redacted);CMTS-MAC=(Redacted);CM-QOS=1.1;CM-VER=3.1;

 

Question

 • 

Updated 

3 months ago

85

4

0

Accepted Solution

internet_enthusiast

3 Messages

3 months ago

I think I'll mark this as the solution post!

Xfinity support confirmed they saw the frequent T3 timeouts on my modem, but to determine what was causing them we needed to get a technician back out. I requested a senior technician to help get to the root of my issue.

The technician was here yesterday, and it took him all of 2 minutes to confirm the signal frequency band looked funky when he hooked in to the line. The first 2 technicians did not identify this issue and said there was no issue because I was getting my promised speed. He traced this issue all the way back to the tap, which means it was effecting more users than just myself. They sent the main line team out the same day to do some emergency work (sorry to say I am not sure what they worked on), which has helped mitigate the issue and now it happens much less frequently. The next step is to bury a replacement line from the tap to my house. Given that it is Minnesota and the winter, it will be spring before they can truly bury the new line. We are seeing if there is a creative way to run a temp line in the meantime (HOA also has to ok the work)

I would say the solution is to be persistent. I went through 3 techs, probably 10 support bots, and 14 hours of my time. If you are having issues with lag, and you have run through the trouble shooting guide and done the leg work to rule out your own equipment: reach out to support via DM either here or on Reddit. And not the AI Xfinity assistant or the front line tech support chat that ghosts you and uses the (frankly useless) automated troubleshooter that tells them nothing obvious is wrong. You yourself know if the service isn't performing well, and Xfinity has people that will help you if you can get there. The care team that has been working with me has been outstanding so far.

The trouble shooting guide listed on this forum:

https://forums.xfinity.com/conversations/your-home-network/connection-troubleshooting-tips/602da777c5375f08cdea3db9

0

XfinityRaf

Official Employee

 • 

853 Messages

3 months ago

Good evening @internet_enthusiast. Thanks for taking the time to post here with your packet loss and lag concerns. If you could please send our team a direct message with your full name and full address, we can look into this for you.

To send a "Direct Message" ("Private") message:

Click "Sign In" if necessary

• Click the "Direct Message chat" icon

• Click the "New message" (pencil and paper) icon

• Type "Xfinity Support" in the "To:" line and select "Xfinity Support" from the drop-down list which appears. The "Xfinity Support" graphic replaces the "To:" line

• Type your message in the text area near the bottom of the window

• Press Enter to send it

0

0

EG

Expert

 • 

109.9K Messages

3 months ago

@internet_enthusiast @XfinityRaf 

Please circle back here and post any possible solutions for the issue here in these open public forums so that all readers here may benefit from the exchange / info. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.

1

internet_enthusiast

3 Messages

Sure, thanks EG. I have connected with Xfinity Support and thus far we have done pretty standard troubleshooting. Re-provisioning the modem, and are beginning to look at the modem logs. No change in speed after the re-provisioning (which wasn't an issue, speed has been what they promised) but also no change in the packet loss. A packet loss test I ran over a 30 second period after the re-provisioning shows high variability in latency (jitter) and over 55% late packets. I noticed 1 of the upstream channels is a little below the specs Xfinity provided so waiting on them to confirm if that's only on my side or if they can see that as well. They have acknowledged they also see the frequent T3 timeouts. I have been asked if I notice any obvious damage to any of the connections/cables either coming into my home or in my home, unfortunately nothing that I can see from the parts that are visible.

Thank you to Xfinity Support for working with me and trying to get this figured out.

Like

Reply

3 months ago

EG

Expert

 • 

109.9K Messages

3 months ago

Thanks for the update thus far ! Good luck with it ! Please update us with a solution if you have one.

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