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Nednats's avatar
Nednats
Dialled in
4 months ago

Hub 5 stuck on DOCSIS 3.0 – Ranging Failures, High Upstream Power, DOCSIS 3.1 Not Engaging

I’m having ongoing issues with my Virgin Media Gig1 connection. Although I’m using a Hub 5, the modem consistently fails to register on DOCSIS 3.1 and falls back to DOCSIS 3.0 after rebooting. This is accompanied by performance instability, occasional packet loss, and errors in the modem logs.

I’ve already:

  • Had the Hub reprovisioned by VM support,
  • Performed full pinhole resets and reboots,
  • Eliminated internal factors (tested with a single device on Ethernet, no VLANs or custom networking),
  • Checked that all coaxial cabling and splitters are secure.

Despite this, the issue persists — and support continues to send boilerplate instructions or suggest a Hub swap, neither of which addresses the real cause.

 

Symptoms:

  • Upstream transmit power: consistently at ~52 dBmV
  • DOCSIS 3.1 channels: detected but not fully locking
  • Repeated modem log entries including:
    • RNG-RSP CCAP Commanded Power in Excess of 6 dB Below DRW
    • T3/T4 ranging timeouts
    • No Unicast Maintenance opportunities received
    • DHCP WARNING – Non-critical field invalid in response

I’ve also monitored performance using ThinkBroadband BQM and observed clear packet loss and latency spikes aligning with the modem errors.

 

Request:

Please can this be reviewed and, if appropriate, escalated to your network or provisioning team? I am happy to accept a technician visit if the purpose is to check the external line or cabinet, but I want to avoid unnecessary in-home diagnostics, which have already been completed.

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  • legacy1's avatar
    legacy1
    Alessandro Volta
    4 months ago

    So how do you know your not on Docsis 3.1? because I'm confused too

    In Status it shows I'm in type docsis 3.0 but can see docsis 3.1 channels listed then in Configuration for Docsis mode is shows 3.1

     

    • Nednats's avatar
      Nednats
      Dialled in
      4 months ago

      That’s a great question and honestly, it’s a bit confusing by design.

      Just because your Hub shows DOCSIS 3.1 channels available or “locked” in the status page doesn’t necessarily mean your connection is actively using DOCSIS 3.1.

      Here’s a quick breakdown:

      • DOCSIS 3.1 channels can appear listed or even "locked", but your modem may still be operating in DOCSIS 3.0 mode if there's an issue with signal quality, provisioning, or upstream compatibility.
      • In the status page, the “Cable Modem Status” or “Primary Downstream Channel” line will often say "DOCSIS 3.0" even when 3.1 is present that’s because it’s falling back to using 3.0 for actual data transport.
      • You can sometimes tell from the logs errors like RNG-RSP, T3 timeouts, or No Unicast Maintenance opportunities suggest that DOCSIS 3.1 tried to engage but failed.
      • The Configuration tab will often show “DOCSIS Mode: 3.1” regardless — that just means the modem supports DOCSIS 3.1, not that it’s currently using it.

      The only definitive way to know if your line is actively running in DOCSIS 3.1 is:

      1. If the modem status shows “DOCSIS 3.1” as the operational mode after startup, and
      2. If you're using an OFDM (3.1) downstream and OFDMA (3.1) upstream profile, without it reverting.

      In my case, it keeps reverting to 3.0 due to upstream power levels and ranging errors.

      Hope that helps clarify!

      • IPFreely's avatar
        IPFreely
        Rising star
        3 months ago

        The primary channel will always show 3.0. Those are the only ones that can be primary channels. 

        The configuration shows 3.1 because that's what your modem has been provisioned to lock to. A 3.1 modem can be provisioned with 3.0 channels and configuration only in which case there's a 3.0 configuration. 

        If provisioned for 3.1, which all VM tiers are, and locked to channels what decides if you use them is how load balancing works on that hardware vendor. It's smart to fill 3.1 first if possible. 

        Don't believe both upstream and downstream need to be OFDMA/OFDM, modems showed 3.1 prior to rollout of OFDMA. 

        Obviously given the software on VM's kit, the 3.1 upstream isn't correctly reported to this day, best to hedge bets.