Intermittent connection issues (MB8600 "UCD invalid or channel unusable")

One other thing I've noticed is that at times, there can be high packet loss. Right now, when I'm running a traceroute to 1.1.1.1 or 8.8.8.8, I'm getting about 30% packet loss. When things are working normally, there's typically no packet loss. (I'm happy to post the full traceroute info, but I believe the forum may have rules that may not allow posting IPs that may reveal too much info.)

When the cable modem log entries happen, that seems to correspond to a complete loss of Internet access, while other times, when there's partial packet loss, the cable modem log entries don't seem to happen.

@minibusy 

This may or may not be the root cause of the problem (YMMV) but it should be addressed regardless. The upstream power is on the high side and it may be intermittently fluctuating even higher to out-of-spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels. It appears that one or more upstream channels aren't even bonded. This is typical of an upstream channel / return path impairment somewhere.

In an effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1000 MHz, bi-directional, and no gold colored garbage from Radio Shack, Home Depot, Target, etc. Splitters should be swapped with known-to-be-good / new ones to test.

Also check the coax cable for any damage such as cuts, nicks, abrasions, kinks, sharp bends, etc.

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two-way splitter connected directly off of the drop from the street / pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

Good luck with it !

I checked my wiring, and did not observe any cuts or sharp bends in the coax. Previously, the coax that came into the house ran through a splitter, with one split going to the cable modem, and another going to an outlet with nothing connected to it. I have just changed it to go directly to the cable modem. To connect the two coax cables, I used a keystone coax jack I had handy (https://www.amazon.com/gp/product/B01MT9VYGM/ ), which says it is rated up to 3 GHz. The connections are now also all tight, but I had not checked the tightness previously, so I'm not sure what the previous state was.

Since the original problem I reported is intermittent, and historically has only occurred for a few minutes once every several days or week or so, I'll have to monitor to see whether this helps.

At the immediate moment, it looks like the upstream power has dropped a bit (44.0-45.0 dBmV) while the downstream power has increased a bit (2.9-5.1 dBmV). It looks like I now have 4 upstream bonded channels, which was also the case before I removed the splitter, so it seems like that situation may have already improved since my original post. Is this upstream power level still concerning? Is the increased downstream power level concerning?

Thanks! I will attempt to follow up after observing for a while and seeing what happens.

Here's the full updated table:

Downstream Bonded Channels

Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected    1 Locked QAM256 20 567.0 3.9 45.5 0 0    2 Locked QAM256 13 525.0 3.0 45.0 0 0    3 Locked QAM256 14 531.0 3.7 45.3 0 0    4 Locked QAM256 15 537.0 3.4 45.1 0 0    5 Locked QAM256 16 543.0 2.9 44.9 0 0    6 Locked QAM256 17 549.0 2.7 44.7 0 0    7 Locked QAM256 18 555.0 2.9 44.7 0 0    8 Locked QAM256 19 561.0 3.7 45.3 0 0    9 Locked QAM256 21 573.0 3.7 45.2 0 0    10 Locked QAM256 22 579.0 3.2 44.8 0 0    11 Locked QAM256 23 585.0 3.0 44.5 0 0    12 Locked QAM256 24 591.0 3.6 44.8 0 0    13 Locked QAM256 25 597.0 4.4 45.3 0 0    14 Locked QAM256 26 603.0 4.6 45.4 0 0    15 Locked QAM256 27 609.0 4.0 45.2 0 0    16 Locked QAM256 28 615.0 3.6 44.9 0 0    17 Locked QAM256 29 621.0 3.9 45.0 0 0    18 Locked QAM256 30 627.0 4.2 45.3 0 0    19 Locked QAM256 31 633.0 4.5 45.5 0 0    20 Locked QAM256 32 639.0 4.5 45.5 0 0    21 Locked QAM256 33 645.0 3.8 45.0 0 0    22 Locked QAM256 34 651.0 3.5 44.8 0 0    23 Locked QAM256 35 657.0 3.5 44.8 0 0    24 Locked QAM256 36 663.0 4.4 45.3 0 0    25 Locked QAM256 37 669.0 4.9 45.8 0 0    26 Locked QAM256 38 675.0 4.3 44.3 0 0    27 Locked QAM256 39 681.0 3.8 45.0 0 0    28 Locked QAM256 40 687.0 3.7 44.9 0 0    29 Locked QAM256 41 693.0 4.1 45.2 0 0    30 Locked QAM256 42 699.0 4.8 45.6 0 0    31 Locked QAM256 43 705.0 5.0 45.8 0 0    32 Locked QAM256 44 711.0 4.9 45.6 0 0    33 Locked OFDM PLC 193 957.0 5.1 45.0 112229 0

Upstream Bonded Channels

Channel Lock Status Channel Type Channel ID Symb. Rate (Ksym/sec) Freq. (MHz) Pwr (dBmV)    1 Locked SC-QAM 17 5120 16.4 44.0    2 Locked SC-QAM 18 5120 22.8 44.3    3 Locked SC-QAM 19 5120 29.2 44.8    4 Locked SC-QAM 20 5120 35.6 45.0

@minibusy 

Looks good ! A nice amount of wiggle room now. Yes, live with it a while now and see. Good luck !

Looks like this probably addressed the issue! I haven't noticed any notable problems in the meantime.

Good to hear ! Thanks for the update !

It looks like the problem actually returned today, although mostly no errors in the cable modem log. The power levels seem mostly comparable to before (2.9 to 5.4 downstream, 44.0 to 45.0 upstream). It sounds like the next step is to schedule a tech, so I'll do that.

@minibusy 

Hmmm... Sorry to hear that. Please post back with another update after the tech visit.

I managed to get a 2-4 PM appointment today. Around 2 PM, an Xfinity truck arrived outside my house and did some work on the utility pole outside my house, and did not interact with me in any way. This work resulted in an Internet outage of about a minute for my house.

Around 3:30 PM, a tech showed up. They measured the line, said it was fine, said the outside outside equipment was also fine, and attributed the problem to our hardware (cable modem or router).

Since the problem is intermittent, I'm a bit skeptical of blaming the hardware (although I know bad hardware can sometimes cause unusual problems). I do have an SB6183 around, though, so I can try swapping that in later tonight. Our router is a Ubiquiti Unifi Dream Machine (entry-level enterprise-grade hardware). When we observe packet loss, the loss is always past the router, and not to the router.

How likely is it that our hardware is actually the issue? Is the 2 PM Xfinity truck likely related to our service call?

The tech also mentioned the possibility of renting Comcast equipment, which we'd prefer not to do, but may have to if that's what's needed to troubleshoot the problem further. The tech speculated that the 2 PM truck was for someone else's service call, but the timing seems too coincidental.

Thanks!

I swapped the MB8600 with the SB6183 last night. The router still occasionally reports some packet loss, so swapping the modem does not appear to have helped. This graph is taken from the Unifi management web interface just now.

Also, you can probably tell I have some reluctance to test swapping my router, because the data appears to show it's not the problem, it's a higher end router than typical consumer grade hardware (so it's perhaps less likely to be a problem), and because it controls the rest of my network; I can't just swap in an average consumer grade hardware and have the 4 other wireless access points connected to the router work. If we really have to swap the router to proceed with debugging further, I suppose that's something that I'll have to do, but it's not a straightforward operation.

(Also, if the problem were continuous rather than intermittent, I'd be happy to test for a small amount of time with a consumer grade router, but given that it's intermittent, I can't just do a brief swap.)