Cm600 connection issues xfinity

[chewy75]

I've been having connection issues with modem on and off for about 6 months. It usually happens when my router, or modem loses power and starts back up. My router is a asus RT-AX86U Pro running asuswrt-merlin firmware.

I spoke to support desk for xfinity and they said my line is clean and shows a healthy signal. They suggested I try manufacture support and here I am.

Any help would be appreciated.
Thanks

Checking on the cm600 logs I noticed that I only have 1 Upstream bonded channel locked, but should have more.

1 Locked ATDMA 3 5120 Ksym/sec 22800000 Hz 57.0 dBmV

Here's the event log
Time Priority Description
2024-12-11, 12:49:18 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:48:29 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:48:23 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:47:34 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:47:31 Critical (3) No UCDs Received - Timeout;;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:47:11 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:46:26 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:46:22 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:49 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:27 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:23 Critical (3) SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:22 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:11 Critical (3) SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:10 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:07 Critical (3) SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:45:00 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:44:57 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:44:04 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:43:17 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:43:13 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:42:22 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:41:31 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:41:24 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:40:41 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:39:50 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:38:13 Critical (3) No UCDs Received - Timeout;;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:37:56 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:37:51 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:37:43 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:37:31 Critical (3) REG RSP not received;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:36:05 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:36:00 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:35:13 Critical (3) No UCDs Received - Timeout;;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:34:56 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:34:51 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:34:03 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.0;CM-VER=3.0;
2024-12-11, 12:33:57 Critical (3) Unicast Ranging Received Abort Response - Re-initializing MAC;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:33:40 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=04:2a:e2:c6:49:5d;CM-QOS=1.1;CM-VER=3.0;
2024-12-11, 12:33:08 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=b0:39:56:45:5a:d0;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;
Time Not Established Notice (6) Honoring MDD; IP provisioning mode = IPv6

[chewy75 · Accepted solution]

So xfinity tech came out today and traced my coaxial cable back to a splitter. My apartment complex is old and the splitter was hidden. To make it worse, the previous tenants set it up with the input/output cables reversed. That combined with my older modem is what was causing the issues. The tech removed the splitter and my old router is now able to connect to 4 Upstream channels.

I'm also getting a new modem this weekend and went with a surfboard sb8200.

Thanks everyone for the help and input. It's much appreciated. Happy Holidays

[FURRYe38]

Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.

Please post a copy and paste of the modems connection status log page.
https://kb.netgear.com/30007/How-do-I-obtain-the-cable-connection-information-from-a-NETGEAR-cable-m...

[chewy75]

Frequency start Value

This field below allows you to modify the frequency the cable modem start with its scan during initialization and registration. Enter the new start frequency and restart the cable modem for it to take effect.

Starting Frequency

Startup Procedure

Procedure	Status	Comment
Acquire Downstream Channel	459000000 Hz	Locked
Connectivity State	OK	Operational
Boot State	OK	Operational
Security	Enable	BPI+
IP Provisioning Mode	Honor MDD	IPv6 only

<tabindex=-1>Downstream Bonded Channels</tabindex=-1>

Channel	Lock Status	Modulation	Channel ID	Frequency	Power	SNR	Correctables	Uncorrectables
1	Locked	QAM256	5	459000000 Hz	-0.1 dBmV	42.5 dB	0	0
2	Locked	QAM256	22	561000000 Hz	0.3 dBmV	41.9 dB	0	0
3	Locked	QAM256	23	567000000 Hz	0.4 dBmV	42.1 dB	0	0
4	Locked	QAM256	24	573000000 Hz	0.6 dBmV	42.2 dB	1	0
5	Locked	QAM256	1	435000000 Hz	0.4 dBmV	42.4 dB	0	0
6	Locked	QAM256	2	441000000 Hz	-0.1 dBmV	42.0 dB	0	0
7	Locked	QAM256	3	447000000 Hz	-0.7 dBmV	41.8 dB	0	0
8	Locked	QAM256	4	453000000 Hz	0.6 dBmV	42.9 dB	0	0
9	Locked	QAM256	6	465000000 Hz	0.4 dBmV	42.8 dB	0	0
10	Locked	QAM256	7	471000000 Hz	0.6 dBmV	42.8 dB	0	0
11	Locked	QAM256	8	477000000 Hz	-0.4 dBmV	42.0 dB	0	0
12	Locked	QAM256	9	483000000 Hz	0.6 dBmV	42.6 dB	0	0
13	Locked	QAM256	10	489000000 Hz	0.1 dBmV	42.3 dB	0	0
14	Locked	QAM256	11	495000000 Hz	-0.1 dBmV	42.4 dB	0	0
15	Locked	QAM256	12	501000000 Hz	0.7 dBmV	43.0 dB	0	0
16	Locked	QAM256	13	507000000 Hz	0.3 dBmV	38.6 dB	0	0
17	Locked	QAM256	14	513000000 Hz	-0.4 dBmV	42.4 dB	0	0
18	Locked	QAM256	15	519000000 Hz	-0.5 dBmV	42.0 dB	0	0
19	Locked	QAM256	16	525000000 Hz	-1.0 dBmV	41.9 dB	0	0
20	Locked	QAM256	17	531000000 Hz	-0.4 dBmV	41.9 dB	0	0
21	Locked	QAM256	18	537000000 Hz	-0.6 dBmV	41.9 dB	0	0
22	Locked	QAM256	19	543000000 Hz	-0.5 dBmV	41.8 dB	0	0
23	Locked	QAM256	20	549000000 Hz	-0.1 dBmV	41.9 dB	0	0
24	Locked	QAM256	21	555000000 Hz	-0.3 dBmV	41.9 dB	1	0

<tabindex=-1>Upstream Bonded Channels</tabindex=-1>

Channel	Lock Status	US Channel Type	Channel ID	Symbol Rate	Frequency	Power
1	Locked	ATDMA	3	5120 Ksym/sec	22800000 Hz	57.0 dBmV
2	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 dBmV
3	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 dBmV
4	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 dBmV
5	Not Locked	Unknown	0	0 Ksym/sec	0 Hz	0.0 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

[FURRYe38]

Cable Connections data is good. 

Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...
https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/

The CM600 is of older model so you may need to upgrade the modem at some point. 

[Kitsap]

Your connection status sheet shows only one upstream bonded channel.  I would expect at least four.  That is an issue Xfinity should correct.

Your CM600 is an older DOCSIS 3.0 modem, I echo the recommendation from @FURRYe38 that you should consider replacement sometime soon.

[plemans]

Your cable connection is not good. At an upstream of 57dbmv, we'd expect your downstream to be pretty low. Probably in the -7.5 to -15dbmv.  That high of an upstream indicates the modem has to send significant power just to reach the hub/cmts. And it tends to be reciprocal. So, if it's takes that much power for the modem to send data to the hub/cmts, it should have lower downstream values. Yours doesn't. It's sitting about 0 (ish). Something in the line is causing resistance one way (like specific attenuators or cable connection issues), or you're using an amplifier to boost a sketchy signal. 

Back to checking the line for amplifiers or other issues because that isn't a good signal level. They need to be roughly representative of each other's values. 

[plemans]

and @Kitsap is correct. You're coming up on end of life for the cm600. Xfinity is pushing docsis 3.1 devices for speed tiers. 

Keep on eye on their mid-split list for the modems with the higher upstream. You don't think you need it until you have it and appreciate the faster uploads. 

https://assets.xfinity.com/assets/dotcom/projects/cix-4997_compatible-devices/2024.08.14%20Full%20Li...

[chewy75 · Accepted solution]

So xfinity tech came out today and traced my coaxial cable back to a splitter. My apartment complex is old and the splitter was hidden. To make it worse, the previous tenants set it up with the input/output cables reversed. That combined with my older modem is what was causing the issues. The tech removed the splitter and my old router is now able to connect to 4 Upstream channels.

I'm also getting a new modem this weekend and went with a surfboard sb8200.

Thanks everyone for the help and input. It's much appreciated. Happy Holidays

[plemans]

Glad you got it resolved!