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jdub8's avatar
jdub8
Settling in
20 days ago

T3 and Sync error after every reboot, causing severe lag and performance issues

Hi

I've been having connection issues for months now, despite multiple engineer visits, and I'm hoping to maybe get this escalated to the Network Team if possible please. 

The Problem

After every single reboot, I consistently get 1 single T3 timeout on one of the 3.0 Upstream Channels (seemingly random which of the 5 it appears on + strangely the connection is slightly better when it's on one of the higher channels - 3 or 4) as well as a SYNC Timing Synchronization failure (SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing) in the network log. 

This causes a delayed, sluggish connection that gradually becomes worse and worse the longer I go without a reboot. Despite decent speedtest results, online video streaming will buffer - even at 1080p, YouTube will take forever to begin a video. When online gaming, gameplay feels sluggish, delayed, and heavy.

I have literally millions of Corrected Errors on the 3.1 Downstream Channel. I know this is usually seen as 'normal' but I thought I'd mention it since I'm getting them at a rate of around 10,000 a second.

What’s strange is:

  • My signal levels (downstream and upstream power, SNR, etc.) look completely normal since the last engineer visit
  • There are minimal pre/post RS errors.
  • The most recent engineer did a BRILLIANT job: replaced the faceplate, upgraded the Super Hub, replaced every coax cable in the house, removed an old splitter and isolator from the attic, and even changed my position at the cabinet. Everything inside the property should be fine now.

It seems like there might be something going wrong further up the line — maybe a problem with upstream channel performance, CMTS timing, or node-level congestion? Is there any way this can be looked into or escalated to the network team?

As it stands, the connection is verging on unusable. The problems exist at all times of the day. The connection never feels normal. Like I say, even at 144p YouTube videos hang for 10 seconds before beginning. Netflix buffers or degrades in quality every time I have a lag spike. Online gaming is out of the question (one funny example is that playing online on FIFA for example, my opponent takes corners, free-kicks a second before I even see them. It honestly feels like my connection is a second or two behind. I also have extremely high, measurable jitter.

6 Replies

  • jdub8's avatar
    jdub8
    Settling in
    20 days ago

    Trying to copy, paste logs but I keep getting a message saying "Content not published. Your post contains invalid HT.ML'

    But the short story is the levels are all good.

    The 3.0 DS Power ranges from 6.6 on Channel 1 progressively dropping until 3.4 on Channel 31. SNR is 43 on every channel.

    3.1 DS Power is 2.0

    3.0 US Power ranges from 42.5 on Channel 0 progressively dropping until 40.3 on Channel 4.

    3.1 US Power is 37.2

    Log messages immediately after reboot:

    26-06-2025 14:22:51 — critical — Cable Modem Reboot because of - HW or Power-On Reset

    26-06-2025 14:22:52 — critical — SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing

    26-06-2025 14:22:56 — critical — No Ranging Response received - T3 time-out

    26-06-2025 14:23:03 — notice — Honoring MDD; IP provisioning mode = IPv4

    26-06-2025 14:23:05 — warning — DHCP WARNING - Non-critical field invalid in response

    26-06-2025 14:23:11 — notice — TLV-11 - unrecognized OID

    26-06-2025 14:23:12 — notice — DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.

    26-06-2025 14:23:23 — notice — REGISTRATION COMPLETE - Waiting for Operational status

    • Anonymous's avatar
      Anonymous
      20 days ago

      Immediately after a reboot, do expect to see all sorts of error messages logged as the hub syncs and reregisters itself with the CMTS. The post above is showing messages from less than 30 seconds from a hardware reboot; yes there will be, and do expect, all sorts of oddball messages. It’s normal.

      "I have literally millions of Corrected Errors on the 3.1 Downstream Channel. I know this is usually seen as ‘normal'

      Yes it is, well this is ‘corrected errors’ yes, and it’s down to most people not actually understanding how DOCSIS 3.1 works and how the VM implementation logs these. Yes it is confusing and alarming, but yes it is perfectly normal.

      Reboot the hub, wait, wait at least an hour, then post the log entries for the past 30 minutes or so and the stats.

    • Tudor's avatar
      Tudor
      Very Insightful Person
      20 days ago

      "escalated to the network team?" it’s very unlikely the the VM staff members on the board or even the customer services agents can escalate problems like this. I should come from a visiting technician. 
      Note: you can ignore any log messages prior to the REGISTRATION COMPLETE MESSAGE.

      Out of curiosity why are you rebooting the hub? I haven’t rebooted my hub5 in months.

      • jdub8's avatar
        jdub8
        Settling in
        20 days ago

        Thanks for replying. 

        I mentioned escalating to the network team because that's what the most recent engineer said would be the next step if all his work didn't resolve things (and unfortunately it hasn't).

        He actually did a great job. Before he came out I was having tens of thousands of Post-RS, Uncorrectable and T1, T2, T3 and T4 errors. It was literally unusable at that point. Strange thing is, for 5 minutes the levels would all be completely within range and then they'd suddenly collapse to circa -17.0 power levels, the T errors would begin and I'd have an hour of downtime.

        Since he came the levels seem good, they're so much more stable but the overall connection just isn't close to being right.

        Out of curiosity why are you rebooting the hub? I haven’t rebooted my hub5 in months.

        Necessity, unfortunately. Before these issues began I had uptime of over 300 days at one point. Now it's closer to 300 minutes.

        I'll use YouTube as an example. Immediately after a reboot it works OK-ish. Every video takes around 10 seconds to begin playing (obviously not ideal) but once it does I can watch at 720/1080p.

        But things progressively degrade the longer the uptime. A couple of hours of uptime and a YT video will take 20 seconds to begin playing and I'll have buffering issues even at 360p.

        This is the case across all devices.

        I have a Fire TV connected via ethernet. Netflix? Watchable immediately after a reboot. Buffer city and eventually 'your Internet speed is too slow for stable streaming' error message. Streaming from my own LAN on Plex? Works immediately after a reboot, but eventually 'your connection is too unstable to stream this video. Check your network or try a lower quality'.

        Video calls/Teams the issues are even more noticable.

        PingPlotter also shows consistent jumps from 22-28ms to 200+ms

  • jpeg1's avatar
    jpeg1
    Alessandro Volta
    20 days ago

    Don't get too concerned with those logs. The important checks are samknows and the BQM.