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jdsel
join:2014-08-17
Bothell, WA

jdsel

Member

[Connectivity] Intermittent SNR drops causing disconnects

Hey everyone, longtime lurker, first time poster

I'm in San Jose, California with Comcast Business Class on the old 27/7 plan. I'm using an SMC D3G cable modem.

Over the last several weeks I've noticed that my connection is dropping at night for a few minutes at a time, then it comes back. I started using the tool at »SMC D3G Logging tool to keep track of my signal, and found that my downstream SNR will intermittently drop really low (less than 25) and then my connection drops. What's odd is that these SNR drops only occur at night - during the day my connection is rock solid. You can see my last two days of signal data here:

»docs.google.com/spreadsh ··· /pubhtml

Times where this happened are 8/15/2014 0:56:10, 8/15/2014 1:47:51, 8/15/2014 2:29:21, 8/15/2014 3:17:57, 8/15/2014 20:54:43, 8/15/2014 21:34:12, and 8/16/2014 20:11:45. You can see that the rest of the time my downstream SNR stays right around 35.

In the past I've had issues with squirrels chewing through the cables on the utility pole, and Comcast has come out to replace that cabling before. To me it doesn't seem likely that that would be the problem this time since the issue is intermittent - I would expect a damaged cable to give me a low SNR all the time.

I also considered that my cable modem might be failing since I've had the same one for 4+ years, but if that was the case I would expect this problem to be completely random instead of only happening at night time.

Any thoughts? I haven't called Comcast yet because it just seems like such an odd problem - I don't want to pay for a tech to come out if they won't be able to find anything wrong and won't be able to fix the problem.

Thanks!

gar187er
I DID this for a living
join:2006-06-24
Seattle, WA

gar187er

Member

probably maintenance doing work on the plant....give it a couple days and see if it goes away....
jdsel
join:2014-08-17
Bothell, WA

jdsel

Member

This has been going on for at least 6-8 weeks.

Streetlight
join:2005-11-07
Colorado Springs, CO

Streetlight to jdsel

Member

to jdsel
What about the other modem parameters - downstream power changes, upstream power changes, frequency changes? Also, if you're watching cable TV, do you see any disruptions? You might need to be watching channels that are at or near the HSI frequencies. If you're asleep at that time, if you have a DVR you might set up a recording and look and see what happens. It very well may mean that some maintenance is going on particularly if you find some improvements in modem parameters.

I had similar problems which was reported in another thread and there was a clear correlation between major changes in HSI and TV pixelation on several high frequency channels. The tech found that a pedestal feeding the one my cable was connected to had an intermittent short circuit and when he wiggled it, the short became permanent and took out the whole neighborhood. On a cold and windy night last winter he and the line tech on call took about three hours to fix the problem.
jdsel
join:2014-08-17
Bothell, WA

jdsel

Member

said by Streetlight:

What about the other modem parameters - downstream power changes, upstream power changes, frequency changes? Also, if you're watching cable TV, do you see any disruptions? You might need to be watching channels that are at or near the HSI frequencies. If you're asleep at that time, if you have a DVR you might set up a recording and look and see what happens. It very well may mean that some maintenance is going on particularly if you find some improvements in modem parameters.

I had similar problems which was reported in another thread and there was a clear correlation between major changes in HSI and TV pixelation on several high frequency channels. The tech found that a pedestal feeding the one my cable was connected to had an intermittent short circuit and when he wiggled it, the short became permanent and took out the whole neighborhood. On a cold and windy night last winter he and the line tech on call took about three hours to fix the problem.

Good point - I was so focused on SNR that I overlooked that everything else is falling apart too. Downstream power is normally around 2-4 dBmV but drops to around -40 or -50 dBmV when this happens. Upstream power drops from around 40 dBmV to -1. The frequencies (both downstream and upstream) change as well - they just go all over the place. For example my downstream frequencies are normally in the 550-620MHz range, but when this happens they're anywhere from 140 - 900 MHz.

I don't have TV service so I can't get any information there.

The problem you had with a short does sound similar to what I'm dealing with, so it may be something like that. I wish there was a more clear, obvious answer so that Comcast doesn't bring a tech out here just for them to not find anything, but with such a weird and intermittent problem that may be the best choice.

Streetlight
join:2005-11-07
Colorado Springs, CO

Streetlight

Member

Get a tech out. A good one wild find the problem. If you can capture modem data when you have this problem and show the tech it might help a lot. If you have neighbors on the same ped or near by, that have Comcast service, it might be worth checking with them about any problems they have.

netengineer
@173.8.164.x

netengineer to jdsel

Anon

to jdsel
It took me a month to have them fix a similar issue effecting all subscribers on the RF cable plant leg of my node here near downtown San Jose. I had to document with PingPlotter every day. They would not tell me what the issue was but I suspect it was the node or their edge QAM gateways. Could have also been a bad amp or ingress noise from some CPE on this particular leg of the node. Pinging the CMTS gateway from outside the Comcast network showed zero packet loss. You can try to give this number a call as it is their "Make it right" team: 1-866-671-5645. That was the only way I could get any traction from them as a Comcast BCI customer.
jdsel
join:2014-08-17
Bothell, WA

jdsel

Member

Alright, thanks for the help and advice everyone. I was hoping to avoid turning this into a big, complicated thing, but it looks like that's how it's going to have to be. Hopefully Comcast is able to figure out the issue in a reasonable period of time without too much back and forth.

In other news I had another drop today that happened at 10:54AM, so apparently it really is random and isn't just happening at night time.

Streetlight
join:2005-11-07
Colorado Springs, CO

Streetlight

Member

According to your original post, you had not called Comcast. Your problem will likely not be solved without getting a tech out to check things out. These problems don't fix themselves. The problem may be very simple to solve such as changing corroded connectors or replacing a cable drop that has been chomped on by squirrels. It might take less than an hour to fix. You can't assume you'll get bad service. Even though one reads about poor service by Comcast support personnel one must remember there are 22 million subscribers and we generally hear from the small percentage that have problems in these forums. People are much more likely to complain than say nice things.
jdsel
join:2014-08-17
Bothell, WA

jdsel

Member

You're correct that I had not called Comcast when I posted this - I was looking for more information first so I might have a better idea of what the problem was before talking to Comcast. Everyone's posts made it clear that the problem could be any number of things and that only a tech would be able to figure it out for sure, so that's when I called Comcast.

I wanted to post a follow-up about what has happened since then. After calling Comcast and having them look at everything, they found that I was getting a significant number of T3 timeouts. The Comcast rep said that this likely indicated a problem with the cable node so we scheduled a tech to come out. Due to my busy schedule (and the fact that this is only an intermittent problem) I scheduled the tech for today, although Comcast originally offered to have someone out within 4 hours.

The tech came out today, listened to my description of the problem, looked at the overhead lines, and told me that he immediately knew what was wrong. At some point (he said it looked pretty recent) a line tech had worked on the feeder line and replaced part of it with the wrong type of cable - he said from the ground it looked like either RG6 or RG11 when it should have been a thicker cable (I didn't get the specifics about which type of cable should have been used). Additionally the tech who did this did not properly weatherproof the cable - there was a blue heatshrink covering around the end of it that was loose. Because of this he said moisture was likely getting into the cable when temperatures dropped or it rained, which explains why my problems almost always happened late at night or early in the morning.

As a result they have to completely replace that part of the feeder line with the correct cable and properly weatherproof it. This was something that today's tech was not able to do, but he scheduled a line tech to come out tomorrow to do it. Once that's fixed I'll keep monitoring my SNR, downstream and upstream power, etc. and see if there are any further issues.

Thanks everyone for your help and advice! As Streetlight pointed out Comcast might have a bad reputation, but despite that they're often able to provide good service. Everyone I've talked to and worked with from Comcast has been friendly and helpful throughout this process.