U

Visitor

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3 Messages

Thu, Aug 12, 2021 6:21 PM

SYNC Timing Synchronization failure

I am getting occasional drops on our MB8600 cable modem on a 1.2 Gbps plan.

Not sure why is going on and the logs with the power levels and SNR are attached below.

Thank you for all the help.

[Image Removed: "Personal Information"]

This post was escalated on August 12, 2021 by EG

Responses

EG

Expert

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89.6K Messages

2 m ago

@user_cf8a45 

Please redact the CM MAC and the CMTS MAC addresses for your privacy.  They are considered to be personal information. Personally identifying 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".

EG

Expert

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89.6K Messages

2 m ago

O/k it seems that your image of the error log entries has now been completely deleted.

Visitor

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3 Messages

2 m ago

Ok the error logs are something like below. Everytime I get this, my internet drops.

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

Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;

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

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

Unicast Maintenance Ranging attempted - No response - Retries exhausted;

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

No Ranging Response received - T3 time-out;

Honoring MDD; IP provisioning mode = IPv6

DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.

EG

Expert

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89.6K Messages

2 m ago

O/k even though the signal stats looked good at that snapshot in time, the error log entries confirm that something is going on. Perhaps there is noise ingress into the line(s) / an upstream channel-return path impairment somewhere.


There are other signal stat figures 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 can check the CMTS (Cable Modem Termination System) 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 !

Visitor

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3 Messages

@EG Thank you so much. I will wait for the reply.

EG

Expert

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89.6K Messages

@user_cf8a45 You're quite welcome ! :-)

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XfinityBrie

Official Employee

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371 Messages

Hey @EG thanks for bringing this to our attention. I'm inclined to agree with your initial thought in regards to possible noise on the line--something is fishy here.

 

@user_cf8a45 can you shoot us a Direct Message with the account information so we can pull the modem and get a closer look? I'll include information below how to send us a direct message.

 

To send a direct message:

 

Please only send a direct message when requested by an official employee--sending a chat when not requested may result in the chat being lost given the high volume of chat requests received daily.

 

  • Ensure you are first signed in, then you will see an icon at the top right of your page. Click that or follow this link: https://comca.st/2VSEfJx
  • From there, click the 'New Message' icon. In the 'To' field, type 'Xfinity Support'.
  • Type your message in the text area that appears at the bottom of the window and hit enter to send. An official employee, such as myself or whoever is first available, will respond.

 

We ask that you please include your name, the account holder name (if different), and the service address. We'll take it from there.

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New Poster

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3 Messages

1 m ago

I also have the SYNC Timing Synchronization failure in my log , a high channel 33 - OFDM PLC # of corrections.

 33 Locked OFDM PLC 159 702.0 2.4 42.5 4022188 0

I am on the 1.2 speed plan , only 1 have I gotten 1.2 speed to my ASUS AXE-11000 router (via router self test) once in the early am out of hundreds of attempts.

The real issue I am having is that I still get drops (periods of no connectivity) on my home network. As I understand it is up to 1.2 speed.

I was going to move the cable modem (brand new) but it is in the kitchen, the drop comes into the basement and it goes into a powered splitter before going to the modem.

However that was needed when we had CATV (~6 tvs) and the cable modem. Now we just use internet (cable modem), so I figure running direct to the modem might solve my issue. But there is an Attenuator and I believe MOCA filter inline (not sure about the MOCA has a red band) "filters" running into the powered splitter. I assume that if I go straight to the modem I will not need a powered amplifier. But I wanted to check, perhaps I will need just an amplifier and not a splitter? Or noting no amp, no MOCA, no attenuator? Or keep just attenuator?

(edited)

This comment has been converted into a post
EG

Expert

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89.6K Messages

@vbip

Depends on the signal strength. What do the modem's signal stats look like ? Try getting them here; http://192.168.100.1  or here http://10.0.0.1 


Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.

What is the exact make and model number of the cable modem ?

Is this a WiFi connection ?

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.

Was your question answered? Please mark an Accepted Answer!tick

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