Please Help Tier 3 Network Operations for Manhattan! [Detailed Analysis]

Jonathan

Please escalate this directly to Tier 3 Network Operations. Thank you!

Issue Summary:

• Severe return-path impairment / CMTS uncorrectables resulting in complete loss of upstream OFDMA carriers.
• Upload speeds dropping from provisioned 40+ Mbps down to ~500 Kbps/1 Mbps.
• Event Log Alarms: Continuous repeating "UCD invalid or channel unusable", T4 timeouts, and SYNC Timing Synchronization failures.
• Physical Line RF Levels (unpadded drop): Downstream raw power is running hot at +12.6 dBmV; upstream transmit drops down to ~25.5 dBmV.

Please check the neighborhood node's PNM (Proactive Network Maintenance) telemetry for return-path ingress/noise and high downstream RF.

Here are the Event Logs from my modem:

Critical DOCSIS Event Log Excerpt (Netgear CAX80 / DOCSIS 3.1):

Mon Oct 12 17:02:25 2026 | Critical (3) | UCD invalid or channel unusable;CM-MAC=[REDACTED];CMTS-MAC=00:90:f0:27:00:00;CM-QOS=1.1;CM-VER=3.1;
Thu Jan 1 00:00:32 1970 | Critical (3) | UCD invalid or channel unusable;CM-MAC=[REDACTED];CMTS-MAC=00:90:f0:27:00:00;CM-QOS=1.1;CM-VER=3.1;
Thu Jan 1 00:00:29 1970 | Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=[REDACTED];CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;
Mon Oct 12 16:17:27 2026 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=[REDACTED];CMTS-MAC=00:90:f0:27:00:00;CM-QOS=1.1;CM-VER=3.1;
Mon Oct 12 16:17:26 2026 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=[REDACTED];CMTS-MAC=00:90:f0:27:00:00;CM-QOS=1.1;CM-VER=3.1;
Mon Oct 12 16:17:18 2026 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=[REDACTED];CMTS-MAC=00:90:f0:27:00:00;CM-QOS=1.1;CM-VER=3.1;
Mon Oct 12 15:35:19 2026 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=[REDACTED];CMTS-MAC=00:90:f0:27:00:00;CM-QOS=1.1;CM-VER=3.1;
Thu Jan 1 00:00:36 1970 | Critical (3) | DHCP FAILED - Discover sent, no offer received;CM-MAC=[REDACTED];CMTS-MAC=00:90:f0:27:00:00;CM-QOS=1.1;CM-VER=3.1;

Diagnostics & Plant Telemetry:

• Upstream OFDMA Channel 1 dropped to Not Locked (0 Hz / 0 dBmV).
• Upstream throughput collapsed to ~500 Kbps/1 Mbps due to severe return-path packet loss.
• Raw unpadded drop RF levels: Downstream is excessively hot at +12.6 dBmV; Upstream transmits at ~25.5 dBmV.
• Issue points to return-path plant impairment/noise ingress on CMTS node (00:90:f0:27:00:00) and an unbalanced outside street tap.

RAIST515O

Reminds me when some workers exposed the coax and sheared off the outer shielding in my neighborhood one summer. Man that made a mess of the signal. Hopefully it is that obvious and just as "easy" to resolve.

James_M

Hi @ Jonathan

There was a known area issue impacting your service. The issue has cleared and everything looks to be working as expected as this time. If you see any other issues, let us know.

Jonathan

@James_M My Upstream OFDMA Channels and four of my downstream channels aren't locking. Downstream power is running hot at +13-14 dBmV. My upstream drops to ~25.5 dBmV. Should I expect all 32 downstream channels bonded? Thanks.

James_M

You are using your own modem, so troubleshooting is limited, Next step would be to schedule a tech visit.

Jonathan

This is an outside issue. I have one six-foot coaxial cable connected from the PoE to my equipment, with no splitters. The downstream power running hot at +13-14 dBmV is on Spectrum's end. I wish you could resolve this on your end without a visit. I have one scheduled, but it is very inconvenient because of remodeling work I'm getting done.