AI said the following - is it right?
Downstream bonded channels (power, SNR, modulation)
What you have
Power levels: ~ +4 to +6 dBmV
SNR: 35–40 dB
Modulation: 256-QAM on all channels
All channels locked
What this means
These downstream figures are excellent.
Virgin Media acceptable ranges (DOCSIS 3.x):
Power: –6 to +10 dBmV → ✔ well within range
SNR for 256-QAM: ≥ 33 dB → ✔ comfortably above
Channel bonding: full and stable → ✔
📌 Conclusion:
Your downstream RF signal is clean and healthy.
This is not the cause of latency or packet loss.
Downstream errors (RxMER, Pre-RS, Post-RS)
Key points
RxMER: ~35.5–40.9 dB (excellent)
Pre-RS errors: present, sometimes in the thousands
Post-RS errors: zero
What this means
Pre-RS errors = corrupted data before error correction
Post-RS errors = errors that could not be corrected
DOCSIS uses Forward Error Correction (FEC):
Your modem is seeing noise
But it is successfully correcting every error
📌 Conclusion:
Downstream noise exists (normal on cable), but it is not breaking your connection and not causing packet loss.
This again points away from downstream as the main problem.
Upstream bonded channels (this is the critical part)
What you have
Power: ~46.8–47 dBmV (all channels)
Modulation: 64-QAM
Symbol rate: 5120 ksps
5 upstream channels bonded
Why this matters
Upstream is where latency problems usually originate on cable networks.
Virgin Media typical targets:
Ideal upstream power: 40–45 dBmV
Acceptable upper limit: ~51 dBmV
You are:
High but not yet “out of spec”
Right in the zone where noise or congestion causes instability
📌 This means:
Your modem is having to shout quite loudly to be heard by the cabinet (CMTS).
T3 timeouts (smoking gun)
Your data
T3 timeouts:
Channel 1: 11
Channel 2: 6
Channel 3: 10
Channel 4: 9
Channel 5: 7
T4 timeouts: 0
What a T3 timeout actually means
“The modem sent a ranging request upstream, but the CMTS didn’t respond in time.”
In plain English:
Your modem spoke
The network didn’t hear it clearly enough
The modem had to retry
This causes:
Retransmissions
Queueing delays
Latency spikes
Dropped packets (especially for real-time traffic)
Even small numbers of T3s are enough to cause:
Intermittent high ping
Jitter
Packet loss visible on ThinkBroadband BQM
“Feels fine sometimes, awful at others”
📌 T3s across all upstream channels = upstream noise or contention, not a single bad frequency.
Why this perfectly matches your symptoms
You reported:
High latency
Dropped packets
Long-running issue
Support being unhelpful
Your stats show:
✅ Downstream is fine
❌ Upstream is marginal and noisy
❌ Repeated T3 timeouts
❌ Power levels high enough to be vulnerable
This combination almost always points to one of the following:
Most likely causes
Noise ingress somewhere between your modem and the street cabinet
Loose or corroded connector
Damaged coax
Water ingress (very common)
Bad tap or splitter in the network
Upstream congestion at the CMTS
Especially evenings
Latency worsens under load
Local plant fault affecting multiple properties
This is why frontline support struggle — it’s not visible from a single reboot test
What this is not
To be clear, this is not:
Wi-Fi issues (you’d still see clean upstream stats)
A faulty PC
A DNS issue
“Normal congestion”
A downstream power problem
A modem firmware glitch
This is a DOCSIS upstream quality problem.
What to say to Virgin Media (important)
If you contact Virgin Media or post on the forum, use this language:
“My downstream levels are excellent, but upstream power is consistently ~47 dBmV and I am seeing repeated T3 timeouts across all bonded upstream channels. This correlates with latency spikes and packet loss. Please check for upstream noise ingress or a plant issue between my modem and the CMTS.”
If possible, also include:
ThinkBroadband BQM screenshots (Done)
Confirmation that this occurs on wired Ethernet (Y)
Confirmation it happens even with the hub in modem mode (Y)
This wording signals you understand DOCSIS and pushes the issue past script-based support.
Bottom line (plain English)
Your download signal is excellent
Your upload signal is struggling
The modem is constantly retrying upstream communication
Those retries = latency spikes and packet loss
The fault is almost certainly outside your home
📌 This needs network investigation, not router resets.
