My wife and I both teach at universities. We are "providing remote instruction" from home.
We have been having service interruptions consistent with some other reports on this board --- clusters of T3/T4 timeouts.
I have ruled out everything downstream from the modem. (The modem logs make it clear that there is a connection issue. My setup is modem -> router -> network, and during these interruptions my router's diagnostics indicate it has lost Internet but there are no issues with physical connections or wifi.)
I have been in touch with XFinity Support but got no help other than suggestion to speak to modem manufacturer (which I did, see below).
I think the signal noise is coming from outside the house. I'm writing to seek support in diagnosing and remedying this issue.
Here is today's example from my modem's logs:
| Tue Sep 22 09:47:56 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out; [macs redacted] |
| Tue Sep 22 09:47:57 2020 | Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;[macs redacted] |
| Tue Sep 22 09:48:00 2020 | Warning (5) | MDD message timeout;[macs redacted] |
| Tue Sep 22 09:48:01 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 09:48:02 2020 | Warning (5) | MDD message timeout;[macs redacted] |
| Tue Sep 22 09:48:11 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 09:48:16 2020 | Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;[macs redacted] |
| Tue Sep 22 09:48:16 2020 | Warning (5) | MDD message timeout;[macs redacted] |
| Tue Sep 22 09:48:22 2020 | Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;[macs redacted] |
| Tue Sep 22 09:48:22 2020 | Warning (5) | MDD message timeout;[macs redacted] |
| Tue Sep 22 09:48:26 2020 | Critical (3) | SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;[macs redacted] |
| Tue Sep 22 09:52:31 2020 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;[macs redacted] |
| Tue Sep 22 09:52:44 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 09:52:49 2020 | Notice (6) | Honoring MDD; IP provisioning mode = IPv6 |
| Tue Sep 22 09:53:35 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 09:54:08 2020 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out; [macs redacted] |
| Tue Sep 22 09:54:20 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 09:54:24 2020 | Notice (6) | Honoring MDD; IP provisioning mode = IPv6 |
| Tue Sep 22 09:55:23 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 09:55:56 2020 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;[macs redacted] |
| Tue Sep 22 10:00:11 2020 | Critical (3) | No Ranging Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 10:01:22 2020 | Critical (3) | Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;[macs redacted] |
| Tue Sep 22 10:01:26 2020 | Critical (3) | No Ranging Response received - T3 time-out;[macs redacted] |
| Tue Sep 22 10:01:34 2020 | Notice (6) | Honoring MDD; IP provisioning mode = IPv6 |
| Tue Sep 22 10:19:25 2020 | Critical (3) | Started Unicast Maintenance Ranging - No Response received - T3 time-out;[macs redacted] |
Here are the connection stats (packet counts reflect 6 days of uptime):
| Downstream Bonded Channels | | |
|
|
| Channel | Lock Status | Modulation | Channel ID | Freq. (MHz) | Pwr (dBmV) | SNR (dB) | Corrected | Uncorrected | | 1 | Locked | QAM256 | 1 | 405.0 | -1.7 | 38.8 | 4767 | 11381 | | 2 | Locked | QAM256 | 2 | 411.0 | -2.1 | 38.7 | 3179 | 6905 | | 3 | Locked | QAM256 | 3 | 417.0 | -2.2 | 38.7 | 2790 | 7287 | | 4 | Locked | QAM256 | 4 | 423.0 | -2.5 | 38.5 | 3028 | 6702 | | 5 | Locked | QAM256 | 5 | 429.0 | -2.6 | 38.7 | 2833 | 7191 | | 6 | Locked | QAM256 | 6 | 435.0 | -2.9 | 38.5 | 2750 | 6837 | | 7 | Locked | QAM256 | 7 | 441.0 | -2.9 | 38.4 | 2915 | 6966 | | 8 | Locked | QAM256 | 8 | 453.0 | -2.8 | 38.4 | 2938 | 6898 | | 9 | Locked | QAM256 | 9 | 459.0 | -2.8 | 38.4 | 2781 | 6383 | | 10 | Locked | QAM256 | 10 | 465.0 | -2.6 | 38.5 | 2919 | 6058 | | 11 | Locked | QAM256 | 11 | 471.0 | -2.6 | 38.3 | 2961 | 6413 | | 12 | Locked | QAM256 | 12 | 477.0 | -2.4 | 38.6 | 2928 | 6291 | | 13 | Locked | QAM256 | 13 | 483.0 | -2.0 | 38.7 | 3075 | 5384 | | 14 | Locked | QAM256 | 14 | 489.0 | -1.5 | 38.8 | 9908 | 6042 | | 15 | Locked | QAM256 | 15 | 495.0 | -1.3 | 35.6 | 20719 | 5684 | | 16 | Locked | QAM256 | 16 | 501.0 | -0.9 | 36.3 | 8104 | 5350 | | Total | | | | | | | 78595 | 107772 |
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|
| Channel | Lock Status | Channel Type | Channel ID | Symb. Rate (Ksym/sec) | Freq. (MHz) | Pwr (dBmV) | | 1 | Locked | ATDMA | 5 | 5120 | 35.6 | 52.5 | | 2 | Not Locked | Unknown | 0 | 0 | 0 | 0.0 | | 3 | Not Locked | Unknown | 0 | 0 | 0 | 0.0 | | 4 | Not Locked | Unknown | 0 | 0 | 0 | 0.0 |
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Usually my modem gets 4 upstream channels, sometimes it gets 1 upstream, it works either way. Our plan is for relatively low speeds.
I called XFinity support about this last week (hence the 6 day uptime -- that's when we power-cycled during diagnostics). XFinity support agreed the open question is whether the issue is the modem, the cable from the modem to the wall jack, or outside my building. XFinity support was unable to offer any help other than suggest I contact the modem manufacturer.
Rep for the modem manufacturer (Motorola MB7420) says that if the modem itself was malfunctioning, the device would most likely be completely inoperable. Rep also says that the error log is consistent with connection trouble upstream (it could be the modem, it's just unlikely). Rep also says that having 1 rather than 4 upstream channels is not necessarily an issue at relatively lower speed plans (like the one we have).
Other people on this board have said that upstream power levels like the one reported here are high. Is it high?
The modem is connected to the wall jack through a daisy chain of 2 coaxial cables:
modem -> coax cable 1 -> coax cable 2 -> wall jack
All of the connections are snug. We've done nothing to disturb those cables so there's no reason to expect a change in the house wiring caused a change in service.
A previous disruption happened one day after an outage was reported in my area.
A disruption happened yesterday and a few minutes afterwards I saw a technician working on a box on a utility pole in the alley behind my building. And another disruption happened again today. All of them show up on the modem's logs.
So I think the signal noise is coming from outside the house.
I welcome suggestions on what to do next, additional information about log readouts, and more information from XFinity/Comcast regarding the state of service in my area.
