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Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast...

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Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast...

Can you let me know whether I can fix an internet connectivity problem myself, or if I need service by Comcast (which might not be in the cards due to COVID-19)?

 

Symptom is that once or twice a day I lose internet connectivity. I can fix it by rebooting the device (Netgear Gateway C3700v2), or often by simply waiting a few minutes. But with working from home & school from home, that can be pretty disruptive. So I really want to fix this.

 

Here are the event logs from when it happened this afternoon:

Time Priority Description
2020-05-04, 05:03:00.0 Warning (5) MDD message timeout;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 05:02:40.0 Warning (5) Unicast DSID PSN startup error
2020-05-04, 05:02:03.0 Notice (6) Honoring MDD; IP provisioning mode = IPv6
2020-05-04, 05:01:46.0 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 05:00:50.0 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 05:00:44.0 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 05:00:44.0 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 05:00:01.0 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 05:00:01.0 Warning (5) MDD message timeout;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 04:59:54.0 Critical (3) SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;
2020-05-04, 04:59:54.0 Warning (5) MDD message timeout;CM-MAC=38:94:ed:d6:41:90;CMTS-MAC=00:38:df:9b:12:41;CM-QOS=1.1;CM-VER=3.0;

 

Any advice how to troubleshoot this?

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Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

In case it's helpful, here's what I'm seeing in terms of connection:

 

Downstream - SNR looks ~32dB right now, pretty sure it was a little over 50dB when I looked earlier today. The line to the street isn't great, Comcast put in an amplifer a few years ago which helped a lot.

 

Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 29 639000000 Hz -4.4 dBmV 31.8 dB 20950 1379
2 Locked QAM256 25 615000000 Hz -3.2 dBmV 33.8 dB 374 1381
3 Locked QAM256 26 621000000 Hz -3.7 dBmV 33.5 dB 416 1403
4 Locked QAM256 27 627000000 Hz -3.8 dBmV 33.2 dB 511 1390
5 Locked QAM256 28 633000000 Hz -4.1 dBmV 32.9 dB 1186 1373
6 Locked QAM256 30 645000000 Hz -4.4 dBmV 32.5 dB 2278 1408
7 Locked QAM256 31 651000000 Hz -5.2 dBmV 31.7 dB 38824 1426
8 Locked QAM256 32 657000000 Hz -5.2 dBmV 31.5 dB 72768 1383

 

Upstream

 

Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 17300000 Hz 53.5 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 23700000 Hz 54.0 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 30100000 Hz 54.0 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 36500000 Hz 54.0 dBm

 

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Diamond Problem Solver

Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

You’ll need a tech out your SNR is indeed tanking (it won’t go over 41-42) and your upstream is also out of spec. Take the levels again at the ground block so you have something to compare with

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Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Thank you @CCAndrew! Much appreciated.  I'll call for a tech if I have to, for now considering it last resort.

 

Sorry for the dumb guy question, but can you let me know what it means to measure it at the block? For example I could bring the router down to the basement & plug it in where the line goes into the signal amplier.

 

Meantime I swapped out a splitter for a coax connector (unknown quality, but it's not gold), and I think (?) I've made things a little better, by the numbers pasted below.

 

With some work I can probably move the cable so that I can connect it directly to the modem. Or I can purchase a new connector of known quality.

 

The connectivity problems are hours apart, and I may not always detect them. So it'd take me a few days to determine whether what I've done so far, actually made a difference in the outcome.

 

Thanks again for any advice.

 

Here's the new numbers:

<tabindex=-1>Startup Procedure</tabindex=-1>
Procedure Status Comment
Acquire Downstream Channel 639000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK  
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 29 639000000 Hz -0.5 dBmV 35.9 dB 20950 1379
2 Locked QAM256 25 615000000 Hz 0.2 dBmV 37.2 dB 374 1381
3 Locked QAM256 26 621000000 Hz -0.1 dBmV 36.9 dB 416 1403
4 Locked QAM256 27 627000000 Hz -0.6 dBmV 36.5 dB 511 1390
5 Locked QAM256 28 633000000 Hz -0.6 dBmV 36.5 dB 1186 1373
6 Locked QAM256 30 645000000 Hz -1.0 dBmV 35.9 dB 2278 1408
7 Locked QAM256 31 651000000 Hz -1.6 dBmV 35.4 dB 38828 1426
8 Locked QAM256 32 657000000 Hz -1.5 dBmV 35.4 dB 72805 1383

<tabindex=-1>Upstream Bonded Channels</tabindex=-1>
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 17300000 Hz 50.0 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 23700000 Hz 50.0 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 30100000 Hz 51.5 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 36500000 Hz 52.0 dBmV

 

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Diamond Problem Solver

Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

You can see you already made an improvement in your SNR and your upstream. But upstream still needs to drop 2-3 dB. Testing your modem (not router)at the ground block was to bypass your house wiring see if those levels you posted were an inside or outside issue

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Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Progress!  I was able to remove another splitter, and a coax connector+ cable, such that there's now a single cable between my modem, and the signal amplifier for the incoming line from the street.

 

Now I'm seeing better signal strength, and so far it seems like connectivity issues are resolved. Fingers crossed!

 

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

<tabindex=-1>Startup Procedure</tabindex=-1>
Procedure Status Comment
Acquire Downstream Channel 591000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK  
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 21 591000000 Hz 5.6 dBmV 37.8 dB 1 0
2 Locked QAM256 17 567000000 Hz 6.2 dBmV 39.0 dB 2 0
3 Locked QAM256 18 573000000 Hz 6.2 dBmV 39.1 dB 7 0
4 Locked QAM256 19 579000000 Hz 6.4 dBmV 39.0 dB 0 0
5 Locked QAM256 20 585000000 Hz 5.7 dBmV 38.6 dB 1 0
6 Locked QAM256 22 597000000 Hz 4.8 dBmV 37.4 dB 0 0
7 Locked QAM256 23 603000000 Hz 4.6 dBmV 37.3 dB 0 0
8 Locked QAM256 24 609000000 Hz 4.1 dBmV 36.8 dB 2 0

<tabindex=-1>Upstream Bonded Channels</tabindex=-1>
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 17300000 Hz 46.5 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 23700000 Hz 46.5 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 30100000 Hz 48.5 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 36500000 Hz 49.0 dBmV
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Diamond Problem Solver

Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Is your modem split before the amp or after? What model of amp?

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Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Modem is split after the amp. I just changed the amplifier to add an active return.

 

Old amplifier: Electroline EDA 2100, +15dB forward, passive return

New amplifier: Arris BDA-42-1-AR-R, +15dB forward, +10dB return


I also swapped out the RG6 cable that supplied power to the amplifier (dog had nibbled through to the shielding...). After checking the levels, I added a 7dB splitter/attenuator. 

 

I think all of the levels are now pretty close to the sweet spot. Fingers crossed for reliable connectivity.

 

<tabindex=-1>Startup Procedure</tabindex=-1>
Procedure Status Comment
Acquire Downstream Channel 459000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK  
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 1 459000000 Hz -0.6 dBmV 40.8 dB 0 0
2 Locked QAM256 2 465000000 Hz -1.8 dBmV 39.9 dB 0 0
3 Locked QAM256 3 471000000 Hz -0.9 dBmV 40.5 dB 0 0
4 Locked QAM256 4 477000000 Hz -1.5 dBmV 40.3 dB 0 0
5 Locked QAM256 5 483000000 Hz -0.9 dBmV 40.8 dB 0 0
6 Locked QAM256 6 489000000 Hz -1.1 dBmV 40.6 dB 0 0
7 Locked QAM256 7 495000000 Hz -1.6 dBmV 40.3 dB 0 0
8 Locked QAM256 8 507000000 Hz -1.7 dBmV 40.2 dB 0 0

<tabindex=-1>Upstream Bonded Channels</tabindex=-1>
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 17300000 Hz 44.0 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 23700000 Hz 46.0 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 30100000 Hz 45.5 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 36500000 Hz 47.5 dBmV

 

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Diamond Problem Solver

Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Your modem should be split before the amplifier. Your setup now, you amplify the signal, then attenuate it back down which doesn’t make sense

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Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Thanks. I moved the splitter before the amplifier. I put the cable modem behind a -7dB port of a three-way splitter. So now there's no attenuator or splitter between the amplifier and the modem.

 

I connected the cable TV line to the -3.5 dB port. I don't have cable TV service, so that's basically inert. There remains  an unterminated -7dB port on the splitter. I've got 75 ohm terminators arriving this week from Amazon.

 

The signal looks pretty good to me:

 

<tabindex=-1>Startup Procedure</tabindex=-1>
Procedure Status Comment
Acquire Downstream Channel 459000000 Hz Locked
Connectivity State OK Operational
Boot State OK Operational
Configuration File OK  
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 1 459000000 Hz 0.6 dBmV 39.0 dB 0 0
2 Locked QAM256 2 465000000 Hz 0.7 dBmV 39.0 dB 0 0
3 Locked QAM256 3 471000000 Hz 0.1 dBmV 38.8 dB 0 0
4 Locked QAM256 4 477000000 Hz 0.6 dBmV 39.1 dB 0 0
5 Locked QAM256 5 483000000 Hz 0.4 dBmV 39.0 dB 0 0
6 Locked QAM256 6 489000000 Hz 0.6 dBmV 39.4 dB 0 0
7 Locked QAM256 7 495000000 Hz 0.5 dBmV 39.4 dB 0 0
8 Locked QAM256 8 507000000 Hz 0.3 dBmV 39.0 dB 0 0

<tabindex=-1>Upstream Bonded Channels</tabindex=-1>
Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power
1 Locked ATDMA 1 5120 Ksym/sec 17300000 Hz 42.5 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 23700000 Hz 42.5 dBmV
3 Locked ATDMA 3 5120 Ksym/sec 30100000 Hz 44.5 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 36500000 Hz 45.0 dBmV

 

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Diamond Problem Solver

Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Looks better but why not eliminate the splitter altogether if it’s not being used (it’s just one more thing that can fail).

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Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Without the attenuation from the splitter, the downstream power goes to about +5 dBmV. Upstream power goes to about +37 dBmV, if I recall correctly.

 

I think those numbers are out of spec, aren't they?

 

Net/net, I was aiming for a setup where downstream power was ~0, and upstream power was about 45 dBmV, with a good signal to noise ratio, something like 40 dB. I thought that was about ideal.

Diamond Problem Solver

Re: Intermittent connectivity problem: MDD Timeout, Sync timing synchronization failure, No unicast.

Everything is a range, you’re not going to get everything equal but your numbers are solid without splitter, amp and attenuator

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