The dreaded T3 timeouts
Hi!
So, about six or so months ago, we had a new cable pulled from the cabinet to the wallbox because of connection issues - 30 year old coax and DOCSIS 3.1 don't make for a fun time. All was good for a while, and then we had a really big batch of latency issues, to the point it would cause pfSense to fail over to our wet string DSL fallback. That resolved itself, but now we're getting T3 issues and disconnects like we were before. Just blips, but enough to knock us out of work calls and the like. Logs are looking like this - forgive the formatting, the new forum backend is unhappy about the HTML the Hub 5 produces!
14-10-2025 11:42:45 critical No Ranging Response received - T3 time-out;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
14-10-2025 01:11:18 error DHCP RENEW WARNING - Field invalid in response v4 option;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
13-10-2025 12:59:17 critical Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
13-10-2025 12:59:17 critical 16 consecutive T3 timeouts while trying to range on upstream channel 8;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
13-10-2025 12:59:10 critical Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
12-10-2025 21:16:26 critical No Ranging Response received - T3 time-out;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
12-10-2025 21:16:25 critical Unicast Maintenance Ranging attempted - No response - Retries exhausted;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
12-10-2025 21:16:25 critical 16 consecutive T3 timeouts while trying to range on upstream channel 8;CM-MAC=8c:9a:8f:13:39:4d;CMTS-MAC=00:01:5c:85:c8:70;CM-QOS=1.1;CM-VER=3.1;
Our DS power levels are really quite high across the DOCSIS 3 channels, ranging from 12.9 to 9.3 dBmV.
The 3.1 stats are:
3.1 Downstream channels
Channel Channel Width (MHz) FFT Type Number of Active Subcarriers Modulation (Active Profile) First Active Subcarrier (Hz)
33 94 4K 1840 QAM 4096 1108
3.1 Downstream channels
Channel ID Locked Status RxMER Data (dB) PLC Power (dBmV) Corrected errors (Active Profile) Uncorrectable errors (Active Profile)
33 Locked 0 6.2 2420655321 8
US specs:
3.0 Upstream channels
Channel Frequency (Hz) Power (dBmV) Symbol Rate (ksps) Modulation Channel ID
0 49600000 34.8 5120 QAM 64 1
1 43100000 35 5120 QAM 64 2
2 36600000 35.3 5120 QAM 64 3
3 30100000 35.5 5120 QAM 64 4
4 23600000 35.8 5120 QAM 64 5
3.0 Upstream channels
Channel Channel Type T1 Timeouts T2 Timeouts T3 Timeouts T4 Timeouts
0 ATDMA 0 0 4 0
1 ATDMA 0 0 7 0
2 ATDMA 0 0 4 0
3 ATDMA 0 0 4 0
4 ATDMA 0 0 4 1
3.1 Upstream channels
Channel Channel Width (MHz) Power (dBmV) FFT Type Modulation
6 10.4 30.0 2K QAM 256
3.1 Upstream channels
Channel Channel Type Number of Active Subcarriers First Active Subcarrier (Hz) T3 Timeouts T4 Timeouts
6 OFDMA 208 74000000 23 0
I wonder if we just need to attenuate down, or if there's something up at the head. What're your thoughts?
