Forum Discussion

philmarland's avatar
philmarland
Joining in
2 days ago

Frequent short upstream outages – T3 timeouts, high power, modulation fallback

Hi,

I’m been experiencing frequent short-term connectivity drops on my Virgin Media fibre connection (Hub 3 in modem mode) for the past month. These outages occur roughly 50 times a day, each lasting 5 to 30 seconds. They’re consistent across all wired and wireless devices and only affect upstream traffic.

Symptoms

  • Continuous pings to 4.2.2.1 time out for 5-30 seconds at a time repeatedly throughout the day.
  • During video calls (e.g. MS Teams), I continue to receive video/audio uninterrupted, but other participants report that my video/audio freezes.
  • When the connection resumes, participants describe a “catch-up” effect, suggesting buffering and delayed upstream delivery.
  • The issue affects all wired and wireless devices simultaneously on the network.
  • Downstream performance is fine outside of these dropouts.

Hub 3 logs show consistent issues:

  • 10/07/2025 20:57:45  critical  SYNC Timing Synchronization failure - Loss of Sync
  • 10/07/2025 20:56:11  critical  No Ranging Response received - T3 time-out
  • 10/07/2025 20:39:19  warning   RCS Partial Service
  • 10/07/2025 12:48:51  critical  SYNC Timing Synchronization failure - Loss of Sync
  • 10/07/2025 12:47:25  critical  SYNC Timing Synchronization failure - Loss of Sync

This is happening regularly throughout the day and night.

Modem stats:

Upstream power levels:

Channel 1: 47.5 dBmV (64-QAM)

Channel 2: 52.2 dBmV (fallback to 16-QAM)

Channel 3: 48.5 dBmV (64-QAM)

Channel 4: 48.5 dBmV (64-QAM)

Channel 5: 47.5 dBmV (64-QAM)

Upstream issues:

  • Channel 2 has modulation fallback to 16-QAM
  • T3 timeouts are logged on upstream channels 1 and 5
  • Power levels above 50 dBmV suggest signal attenuation or return path issues

Downstream stats are within acceptable ranges:

  • SNR 37–40 dB
  • Power levels between –1.5 to –3.7 dBmV
  • All channels locked at 256-QAM
  • Some Post RS errors on lower channels, but no complete downstream loss

Request for help

This appears to be an upstream signal quality issue, not a LAN or in-home problem.

Could this be investigated further? Specifically, I’d like:

  • A check on the line quality and return path from my property
  • Inspection of upstream noise, power levels, and cabinet-side performance

Happy to supply more logs or test results as needed. Thanks in advance.

Phil. 

5 Replies

    • philmarland's avatar
      philmarland
      Joining in
      18 hours ago

      Thanks Cardiffman282. This problem has been going on for over a month but I've only just been able to work out that it's definitely not my internal network after I replaced my router etc. The service status page says "Intermittent signal in your area" but nothing more than that. I'm not sure that's related or not though. The problem certainly hasn't gone away of its own accord though.

  • jmbalexander27's avatar
    jmbalexander27
    Just joined
    14 hours ago

    Similar problems for a month or so now. New hub today, mobiles all connecting just laptop having WiFi but no internet. Just went to local tech shop and joined their WiFi and through to internet just like normal. wth?

  • Tudor's avatar
    Tudor
    Very Insightful Person
    14 hours ago

    Your signal levels, both upstream and downstream indicate to me that you are probably a long way from the street cabinet. You need a technician’s visit and possibly moving to a lower attenuated tap on the street cabinet. I am the furthest location from the street cabinet and technicians have moved me to the wrong tap when they have installed other users. Every time I see a VM van in the street I throughly check out my connection!

    • philmarland's avatar
      philmarland
      Joining in
      11 hours ago

      Thanks Tudor. I agree with your suggestion I've been moved around in the cabinet when someone else has been installed. I've had exactly the same problem before and an engineer visit to the cabinet was required to fix it. It had been fine for ages then suddenly it's back with a vengeance. I'm hoping the readings are obvious enough that they can get back on good signal strength all the time as it's made the internet virtually unusable for calls.

      An engineer is coming out on Monday morning apparently.