Dropping Connection, T3 Timeouts, Unicast Maintenance Ranging No Response

The SNR is low to out of spec on the higher frequencies starting at downstream channel 19. Seems that there is noise ingressing in to the line somewhere. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, and latency problems.

In a self troubleshooting effort to try to obtain better connectivity, 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 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

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.

Did the wiring changes recommended by EG help?  I'm having very similar issues and have been unable to get a response from Comcast or through this forum.  Hopefully, you'll have better luck as the issue may be ingress noise in the plant outside your home.

Thanks for your reply.  I was finally able to get up into the attic this morning to check things out.  I am able to trace the coax cable (RG6) from the corner where it enters my house to the modem.  It is a single cable run without any splitters or extra connections. 

There is a cable connection box in my neighbor's front yard, and when we moved in to this house, Comcast had to run an underground line from there, under the street, and it comes up in the corner of myhouse There is a box low on the exterior wall that is labeled TV.  The coax cable comes up from there, and has a singe Female to Female bullet connector that transitions to my house coax cable.  That single cable goes straight to my modem.  We do not have cable TV, and the other coax cable that appears at the corner of my house next to my one for the modem has been abandonded.  

All that to say, my wiring is as good as possible without relocating my modem to directly where the Comcast coax comes into my house.  As it is right now, there is around 75-100 feet of cable total from the corner of the house, to the modem.  Likely the cable running under the street to the Comcast box at the neighbor's house is around 100ft.  

I have been completely unsuccessful in my attempts to get a tech to take a look at this problem.  Every time I have tried to chat with a customer service rep, they just say I need to reboot my modem, and they will re-provision the line, or something like that.

I was hoping I would find a big splitter in the attic, but I guess it isn't going to be that easy.  

I was able to call Comcast and they are quite insistant that I need to eliminate the possibility that this is caused by my wifi router.  They have asked me to plug a computer into the modem via ethernet cable and verify that connectivity issue still exists.  I asked them to explain to me how my router could be causing the system log error seen in my modem, and they just said that they needed me to do that.  I told them that would not work for me.  I am not able to have only one computer connected to the back of the modem while everyone is working from home and trying to do remote schooling.  I asked them how my router would cause signal timeout errors on my modem's system log, and they were unable to answer that question.  Very frustrating.

Comcast offered to send a tech to do "field research" which I believe means checking the signal outside of the house, but not coming into the house.  I told them that would be great, and they will call me to schedule when they can come out.  

Does this sound like a reasonable response?  Should I be purchasing a new modem or router?  

Thanks again.

The low SNR is a physical problem with the connection to the Comcast system. It is not a LAN side problem. A new modem will not fix a coax cable signal impairment.

Thanks for the advice.  It didn't make sense to me that this issue would be related to my lan in any way.  Comcast does a poor job in educating its customer service reps on the technical side of things from my perspective.  

I called Comcast just now to check on my appointment, and whoever I spoke on Saturday said they would create a ticket, but they never did.  I was able to get someone to actually create a ticket, and I'm again waiting for them to contact me with a time/date.  At least this representative seemed to agree that it was a signal strength issue, and did not even bring up the idea that it was caused by my router.  Blah, super frustrating.

Low SNR and traffic congestion are two different types of impairments.

Is there some reference information that would help me understand what "acceptable" signal strength levels are?  Is there a range that my SNR shoud be within?

North of 35 dB, ideally more than 40 dB

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@dbaumbach wrote:

Is there some reference information that would help me understand what "acceptable" signal strength levels are?  Is there a range that my SNR shoud be within?

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So Comcast just came out to do its field research on my cable line.  The tech was very helpful and knowledgeable, and informed me that:

1.  The cabling in my house does not have any problems.  Straight run from the corner of the house to the modem without any splitters.

2.  The line running from my house, under the street, to the pedestal has a lot of interference on it.  He said that a construction crew will be scheduled to replace the line within the next two weeks.

3.  There are some issues at the pedestal with interference from my neighbor's houses backfeeding and potentially affecting my signal.  

But he felt that replacing my drop under the street would resolve the issues I am having.  He said that I might notice a more reliable signal now, from the maintenance work he did in the pedestal, but my SNR read at the modem has not changed much.  He also said that my node is not overloaded, which is good apparently.  I'll look forward to getting a new underground line, and hopefully this issue resolved for good.

What would have to be done to resolve the issue with neighbor's interference coming back through the pedestal connection and degrading my signal?