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Old 08-10-2019, 12:01 PM
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Help me understand my modem?


Can someone help me decode my modem status?

I got a new DOCSIS 3.1 modem, Netgear CM1200. Comcast is my provider. It seems to be working fine, I'm getting more than the 250 down that I'm paying for, and about 10 up. All 32 downstream channels are locked, but only one upstream channel. Comcast over the phone were clueless about what I should expect. I realize not all 8, but it should be more than 1.

Comcast engineer is coming tomorrow, and I'd like to understand what I should be looking for.

pdf of modem status here:
https://drive.google.com/file/d/1Eml...vXxu78KX3/view

32 locked downstream channels show power 2-3 dBmV, signal-to-noise 40-42 dB. The 1 locked upstream channel shows power 43.5 dBmV, but there's no signal-to-noise column displayed for upstream. Are these the parameters I should be looking at, and are they normal? Do the "Downstream OFDM" and "Upstream OFDMA" channels shown at the bottom matter?
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Old 08-10-2019, 12:14 PM
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nm

Last edited by Riemann; 08-10-2019 at 12:15 PM.
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Old 08-10-2019, 12:17 PM
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Event log shows this kind of thing repeated over and over again:

Quote:
Sat Aug 10 10:11:00 2019 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=[snipped];CMTS-MAC=[snipped];CM-QOS=1.1;CM-VER=3.1;

Sat Aug 10 10:10:45 2019 Critical (3) 16 consecutive T3 timeouts while trying to range on upstream channel 3;CM-MAC=[snipped];CMTS-MAC=[snipped];CM-QOS=1.1;CM-VER=3.1;

Sat Aug 10 10:10:45 2019 Critical (3) Ranging Request Retries exhausted;CM-MAC=[snipped];CMTS-MAC=[snipped];CM-QOS=1.1;CM-VER=3.1;

Sat Aug 10 10:10:45 2019 Critical (3) No Ranging Response received - T3 time-out;CM-MAC=[snipped];CMTS-MAC=[snipped];CM-QOS=1.1;CM-VER=3.1;
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Old 08-12-2019, 01:24 PM
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To return to my own unanswered question after Comcast engineer visit in case anyone has similar issues...

The engineer found that a filter had been installed at the street end of my line, which he said was probably installed by a passing engineer who had found noise coming from my line but who had not followed up to figure out why. (That's not unreasonable, perhaps I wasn't home; but it doesn't account for why the problem wasn't addressed when a Comcast engineer came to set up my original service a couple of years ago.) We found the mundane source of the problem: inside my house, somebody had crudely stapled the coax cable to floor beams in several places. It was squashed flat. It's a remarkable testament to how robust coax cable is that I had been getting a stable 300 Mbps downstream through this. (I guess it's because 0's are not really circular but kind of oval, so they still fit?)

Anyway, fortunately I know enough about my crawlspace by now that we traced the route of the cable and managed to use the old cable to pull completely new coax all the way through from the wall outlets. Problem solved, there's now brand new cable all the way from my modem to the street, I have 32 down and 4 up channels locked, and I can waste my money on upgrading to Gigabit service if I feel the urge.

ETA: and my modem event log has been completely clear for 24 hours! I didn't know that was possible...

Last edited by Riemann; 08-12-2019 at 01:27 PM.
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Old 08-12-2019, 01:54 PM
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Has there been an improvement to your upstream rate? Comcast limits me to about 12 Mbps up. And that's with new cable (I get about 250 Mbps down).

Last edited by Dag Otto; 08-12-2019 at 01:54 PM.
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Old 08-12-2019, 07:12 PM
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No, the rate has not changed, I think I'm limited to ~10 Mpbs up, and I guess the single channel could handle that. The service was actually working fine before despite this, and I generally try to avoid interacting with Comcast unless something is on fire. But I upgraded my modem & router and I have been installing a whole bunch of smart home devices, so I just got on a mission to track down what was going on.
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