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

Recently I've started to notice intermittent internet drops throughout the day. I decided to poke around the modem logs and saw these messages.

Fri Jul 29 13:26:16 2022	Critical (3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Fri Jul 29 13:26:16 2022	Warning (5)	MDD message timeout;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Fri Jul 29 13:26:54 2022	Critical (3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Fri Jul 29 13:26:58 2022	Warning (5)	MDD message timeout;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Fri Jul 29 13:27:10 2022	Critical (3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Fri Jul 29 13:27:10 2022	Warning (5)	MDD message timeout;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Fri Jul 29 13:27:23 2022	Critical (3)	SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Fri Jul 29 13:27:25 2022	Critical (3)	SYNC Timing Synchronization failure - Failed to acquire FEC framing;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Sat Jul 30 08:49:05 2022	Critical (3)	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Sat Jul 30 08:49:05 2022	Critical (3)	Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Sat Jul 30 08:49:05 2022	Critical (3)	16 consecutive T3 timeouts while trying to range on upstream channel 1;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Sat Jul 30 09:13:11 2022	Critical (3)	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Sat Jul 30 09:13:11 2022	Critical (3)	Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Sat Jul 30 09:13:11 2022	Critical (3)	16 consecutive T3 timeouts while trying to range on upstream channel 1;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;
Sat Jul 30 09:22:42 2022	Critical (3)	Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=xxx;CMTS-MAC=xxx;CM-QOS=1.1;CM-VER=3.0;

Here's what I see for downstream channels.

Channel	Lock Status	Modulation	Channel ID	Freq. (MHz)	Pwr (dBmV)	SNR (dB)	Corrected	Uncorrected
1	Locked	QAM256	24	531.0	4.9	40.3	136569	90124
2	Locked	QAM256	25	537.0	5.0	40.3	133760	95526
3	Locked	QAM256	26	543.0	5.2	40.3	132297	93846
4	Locked	QAM256	27	549.0	5.2	40.3	127270	86335
5	Locked	QAM256	28	555.0	5.3	40.2	124281	86301
6	Locked	QAM256	29	561.0	5.1	40.3	124939	86619
7	Locked	QAM256	30	567.0	5.4	40.3	122802	82731
8	Locked	QAM256	31	573.0	5.4	40.2	121373	79714
9	Locked	QAM256	32	579.0	5.3	40.3	123097	95027
10	Not Locked	Unknown	0	585.0	0.0	0.0	125299	81094
11	Locked	QAM256	34	591.0	5.3	40.2	123114	96758
12	Locked	QAM256	35	597.0	5.0	40.2	147182	94826
13	Locked	QAM256	36	603.0	4.5	38.6	129224	97700
14	Locked	QAM256	37	609.0	4.2	39.8	125074	97701
15	Locked	QAM256	38	615.0	4.1	40.1	128848	108166
16	Locked	QAM256	39	621.0	3.9	40.1	176645	256552
17	Locked	QAM256	40	627.0	3.5	41.1	191098	217355
18	Locked	QAM256	41	633.0	3.3	41.1	191030	156593
19	Locked	QAM256	42	639.0	3.3	40.9	187535	162370
20	Locked	QAM256	43	645.0	3.7	41.1	194263	178027
21	Locked	QAM256	44	651.0	3.6	40.9	225789	192978
22	Locked	QAM256	45	657.0	3.4	40.9	345668	206262
23	Locked	QAM256	46	663.0	3.2	40.8	566630	221968
24	Locked	QAM256	47	669.0	3.0	40.8	805817	263532
Total							4809604	3228105

And for upstream

Channel	Lock Status	Channel Type	Channel ID	Symb. Rate (Ksym/sec)	Freq. (MHz)	Pwr (dBmV)
1	Locked	ATDMA	8	5120	22.8	42.7
2	Locked	ATDMA	6	2560	10.4	42.8
3	Locked	ATDMA	7	5120	16.4	42.8
4	Locked	ATDMA	9	5120	29.2	42.9
5	Locked	ATDMA	10	5120	35.6	42.9
6	Locked	ATDMA	12	2560	40.4	41.3
7	Not Locked	Unknown	0	0	0	0.0
8	Not Locked	Unknown	0	0	0	0.0

I have no idea what I'm looking at. Does anything look suspicious? Thank you!!

Responses

U

user_00a52e

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8 Messages

3 years ago

This is on a Motorola MB7621 modem.

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Please redact all of the CM MAC and the CMTS MAC addresses in your error log entries for your privacy. They are considered to be personal information. The posting of personally identifiable information is a violation of their forum guidelines. The forum bot will not allow your post to be seen publically. It flagged your post as "Private".

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user_00a52e

Visitor

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8 Messages

3 years ago

Looking at some past posts on this forum, looks like it could be something with my cables upstream? I was just looking at my setup and noticed a completely unnecessary splitter on my coax that's basically serving as an extension. Will try removing that and see.

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EG

Expert

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110.3K Messages

3 years ago

@user_00a52e

You haven't redacted those MAC addresses from the error log entries as advised. Your post is still "Private"...

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U

user_00a52e

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8 Messages

@EG have removed those addresses

3 years ago

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EG

Expert

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110.3K Messages

3 years ago

The signal stat values were all good at that snapshot in time, except for downstream channel number 10. It's not locked in. Noise ingress into the line(s) somewhere can cause that. The error log entries and the number of "uncorrected" bit errors also point in that direction.

Also. There are other signal stat values that can't be read by the modem. They are the "Upstream Rx Power" (Upstream Receive Power Level), the "Upstream SNR Ch." (Upstream Signal To Noise Ratio), and the "Upstream ICFR" (In Channel Frequency Response). These are as equally important in diagnosing connectivity issues as are the modem's stats.

I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. They will be able to poll the CMTS (Cable Modem Termination System) to check for any real-time degradation and / or error reports, see your node / cable plant, and modem health, and see whether or not everything is in the green zone. They can also see a history plot for the modem and poll for those upstream receive signal stats.

You should get a reply here in your topic. Good luck !

(edited)

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U

user_00a52e

Visitor

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8 Messages

3 years ago

I removed the unnecessary splitter in the coax connection to my modem. Now the channels look like this.

That unlocked downstream channel is gone. The powers on the downstream and upstream have shifted. Although this is a snapshot right after reset so maybe it'll look different later..

Down

Channel	Lock Status	Modulation	Channel ID	Freq. (MHz)	Pwr (dBmV)	SNR (dB)	Corrected	Uncorrected
1	Locked	QAM256	24	531.0	12.9	40.3	0	0
2	Locked	QAM256	25	537.0	12.8	40.3	0	0
3	Locked	QAM256	26	543.0	12.9	40.3	0	0
4	Locked	QAM256	27	549.0	13.1	40.3	0	0
5	Locked	QAM256	28	555.0	13.2	40.3	0	0
6	Locked	QAM256	29	561.0	13.2	40.3	0	0
7	Locked	QAM256	30	567.0	13.4	40.3	0	0
8	Locked	QAM256	31	573.0	13.5	40.3	0	0
9	Locked	QAM256	32	579.0	13.5	40.3	0	0
10	Locked	QAM256	33	585.0	13.4	40.3	0	0
11	Locked	QAM256	34	591.0	13.3	40.3	0	0
12	Locked	QAM256	35	597.0	13.0	40.2	0	0
13	Locked	QAM256	36	603.0	12.6	38.4	0	0
14	Locked	QAM256	37	609.0	12.3	39.7	0	0
15	Locked	QAM256	38	615.0	12.2	40.1	0	0
16	Locked	QAM256	39	621.0	12.0	40.1	0	0
17	Locked	QAM256	40	627.0	11.7	40.6	0	0
18	Locked	QAM256	41	633.0	11.5	40.7	0	0
19	Locked	QAM256	42	639.0	11.5	40.6	0	0
20	Locked	QAM256	43	645.0	11.8	41.0	0	0
21	Locked	QAM256	44	651.0	11.8	40.8	0	0
22	Locked	QAM256	45	657.0	11.8	41.0	0	0
23	Locked	QAM256	46	663.0	11.8	40.5	0	0
24	Locked	QAM256	47	669.0	11.7	40.6	0	0
Total							0	0

Up

Channel	Lock Status	Channel Type	Channel ID	Symb. Rate (Ksym/sec)	Freq. (MHz)	Pwr (dBmV)
1	Locked	ATDMA	6	2560	10.4	34.0
2	Locked	ATDMA	7	5120	16.4	34.3
3	Locked	ATDMA	8	5120	22.8	34.5
4	Locked	ATDMA	9	5120	29.2	35.0
5	Locked	ATDMA	10	5120	35.6	34.8
6	Locked	ATDMA	12	2560	40.4	34.3
7	Not Locked	Unknown	0	0	0	0.0
8	Not Locked	Unknown	0	0	0	0.0

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U

user_00a52e

Visitor

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8 Messages

3 years ago

Also, looking at my first snapshot, the ratio of uncorrected packets to corrected packets is 3228105 / 4809604 = 67%. According to https://www.motorolacable.com/documents/CableConnection.pdf, this number should be 20% or below.

Since I just reset the modem, both these numbers are small now. Will monitor.

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U

user_00a52e

Visitor

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8 Messages

3 years ago

It's been over a day now. I haven't experienced any drops in internet on my devices so that's good news.

Looking at the modem's logs, I don't see any of those T3 time-out events anymore. The log is completely empty.

I still see a very large number of uncorrected events. From what I gather reading other posts, my number is too high.

Channel	Lock Status	Modulation	Channel ID	Freq. (MHz)	Pwr (dBmV)	SNR (dB)	Corrected	Uncorrected
1	Locked	QAM256	24	531.0	13.8	40.3	3021	2195
2	Locked	QAM256	25	537.0	13.7	40.3	3184	2505
3	Locked	QAM256	26	543.0	13.8	40.3	3162	2996
4	Locked	QAM256	27	549.0	13.9	40.3	3583	3422
5	Locked	QAM256	28	555.0	14.0	40.3	3985	4207
6	Locked	QAM256	29	561.0	14.1	40.3	4509	4845
7	Locked	QAM256	30	567.0	14.3	40.3	4971	5726
8	Locked	QAM256	31	573.0	14.4	40.3	5454	6921
9	Locked	QAM256	32	579.0	14.5	40.3	5952	7836
10	Locked	QAM256	33	585.0	14.4	40.3	5996	9214
11	Locked	QAM256	34	591.0	14.3	40.3	6232	10270
12	Locked	QAM256	35	597.0	14.0	40.2	6504	11519
13	Locked	QAM256	36	603.0	13.6	39.0	6446	12258
14	Locked	QAM256	37	609.0	13.2	39.9	6256	13483
15	Locked	QAM256	38	615.0	13.1	40.1	6075	13420
16	Locked	QAM256	39	621.0	12.9	40.2	6041	13256
17	Locked	QAM256	40	627.0	12.5	40.8	5965	10831
18	Locked	QAM256	41	633.0	12.4	40.8	6334	10278
19	Locked	QAM256	42	639.0	12.4	40.8	6330	9866
20	Locked	QAM256	43	645.0	12.8	40.7	6208	9439
21	Locked	QAM256	44	651.0	12.8	40.9	6518	8883
22	Locked	QAM256	45	657.0	12.8	40.8	6260	8603
23	Locked	QAM256	46	663.0	12.8	40.7	6056	8692
24	Locked	QAM256	47	669.0	12.7	40.6	6302	8249
Total							131344	198914

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EG

Expert

•

110.3K Messages

3 years ago

If you are no longer having any connectivity problems, then don't sweat it. Hope things hold up for you. Good luck !

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

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