Cable Modem T4 Timeouts + Network Jabbering + Asus RT-N66U

[kijutsu]

Good evening folks,

I have Comcast's crappy service and I get nonstop T3 and T4 timeouts on the modem.

I've been told it's on my end 'cause the signal looks fantastic on this end'. From what I can find, the numbers look good on this end as well. I was told that I probably have a jabbering network device somewhere that's making the modem crap out. I call BS on this, cause I can bypass everything, do a direct connection with any of 4 different systems I have here and the nonstop T3s and T4s still occur.

What else can I do to verify it's not my end so Comcast doesn't charge me a ridiculous 99.95 fee 'just to come out and tell you it's your problem, not ours.' Exact words from the Comcast Phone Tech.

Any help you can provide would be most appreciated.

 

[PrivateJoker]

Does your coax come inside and that first thing it connects with is the cable modem?

Is your coax grounded on its way into your home?

Do you have an amp anywhere in your coax distribution?

Do you have the comcast phone service? If yes, the modem drops it too? If not, sign up for it because they will troubleshoot it somewhat extensively (they have replaced amps & distribution equipment on telephone poles on both sides [within 50' each direction] of me) in an effort to troubleshoot phone problems, maybe because they're less subjective & open to interpretation than Internet connectivity, then cancel it within the first 30 days so it doesn't even cost you anything. Getting comcast to make my "Digital voice" bulletproof had the side effect of making my internet bulletproof. Past the first trouble ticket they would roll 2-3 trucks out for each digital voice service call! And I never paid for those visits.

 

[stevech]

They charge you to do a service call? Here, the not so loved Time Warner does not, and will help the subscriber get the end to end to work correctly.

Do you have an IP layer problem/symptom such as persistent ping time/lost ping problems-- measured by pinging your first gateway in their system, using a wired-PC (not WiFi)? Tracert will tell you the IP of the first gateway. If you ping that a lot, or use pinplot (freeware) to let it run for hours and plot the result, and if there are faults, then you have evidence for them. If you see such flaws, connect that PC directly to the modem (bypass your router), turn on the software firewall on that PC since you have no NATing router now. Then run the ping/pingplotter test. If this fails too, then try do do it again with a different PC. If this too fails, you have evidence to give them that should demonstrate that the problem is theirs, not your gear, and the Internet itself is not in the loop.

If this is a common DOCSIS cable modem, many have a web page you can view. On Motorola's modems, you can go to 192.168.100.1 and see their pages. One of the pages is signal strength. You should look for a multi-day consistent reading something like:
downstream (them to you) about 0dBmv plus/minus 8
upstream (you to them), about 40dBmv plus/minus 15
The upstream will vary - if their cable plant is having noise and issues, the upstream will increase due to commands from THEIR head-end system- which adjusts your modems upstream power to try to normalize it at their end.

I'll assume that you do not see loss of synch where the LED on the modem showing UP and DOWN or something like that is blinking. Normally the data traffic LED blinks due to activity.

The techs here measure the up/down signal levels, check that you don't have more than one 2-way splitter in the coax from the modem to the incoming cable from them. The check all the coax connectors in your and their equipment to the "demarcation point" and on. They are told to get it right, so that at least your or their PC will work properly independent of the modem.

In my home, there's a 20 year old piece of RG59 coax from my home to their demarc point, not underground, about 100' long. Passing through property I don't own. I had them put an amplifier in my attic that amplifies the UPSTREAM as well as the downstream (most don't do that). That made all the difference.. the upstream was often rising from 45 to 59dBmv (max) and that wasn't enough. It varied by weather conditions. The Amp put about 12dB gain in the upstream.

I hope the modem is theirs, rather than one you bought - to avoid finger-pointing.

 

[kijutsu]

@PrivateJoker:

Direct drop to cable modem via a two-way splitter to attenuate the signal strength (-3.5db on both sides), the other side of the splitter is terminated.

The coax is grounded to the water spigot outside. There is no other equipment attached to the coax cable, no TVs, no phone modems, just the single cable modem. Which is a Motorola SB6141.

@stevech:

Yes, they charge when it's 'customer equipment' causing the problem, because I have a business account due to needing unlimited bandwidth, with having a few web servers and an internet radio station running 24.7.365.

I'm very versed in usage of the cable modem status page and have been on a near constant refresh on it. Down signal strength on all 8 channels range from 36 to 38. Up signal strength is 38 & 40 respectively on the two channels. The problem being, somewhere I'm snagging T3 and T4 timeouts from somewhere, and eventually the cable modem resets to resync the failed upstream signal, thus cutting internet for about 10 minutes at a time.

It is my own cable modem because 10 bucks a month for rental is )#*ing absurd.

 

[stevech]

I pay $5 or so more a month to use THEIR modem so that THEY must make it work right at THEIR expense, and quickly.

For many service calls over 12 years, it's far better to not own the modem, in my opinion.

The dowstream signal strength you report seems odd.

If the modem is dropping synch - and if you have but ONE splitter (2-way) between the modem and the incoming service - make them decide on what's causing it. If they refuse, because they don't own the modem - best you can do is negotiate based on being a high priced biz customer. With my ISP, biz customers get faster response to trouble tickets. My ISP would probably bring out their modem and RF test set and look for a few minutes. If you have a flaky coax connector or too many splitters, or some such, they won't likely see it.

Beware too this gotcha: a bad coax or barrel or splitter can have a tiny air gap in the center conductor. The high freq. downstream is little affected; the upstream, lower at like 30MHz, is greatly attenuated (downstream is like 10x the freq of the upstream.)

Maybe you need to rent from them for 2-3 months to prove/disprove who's at fault on the wiring or owned-modem.
Even the business account may have Terms and Conditions that prohibit running web servers- watch out.

 

[PrivateJoker]

For comparison, here is a screenshot of my Arris, no T3/T4 errors.

@stevech, what do you think (in your expertise) of my levels here?



The last tech that was at my house with one of those full JDSU scanners said my line looked a little hot coming back in the upstream direction. I never did anything about it, and they never did either. . .

To OP, I think @stevech's suggestion of temporarily renting a modem from your ISP, and potentially even trying my idea of signing up for digital voice too could get this hammered out with as little a monetary impact on you as possible. I think the digital voice is the most difficult thing for them to get into a person's house and be trouble free (like it is less tolerant to signal problems), so it's a win/win for your internet, and you're not out anything if you cxl the digital voice quickly.

Also, once you decide your plan of attack (i.e. leasing a modem from them, and/or signing up for the digital voice [if you called them on the phone and asked for free HBO for a few months just for signing up for DV, they'd probably give it to you]), and after you make your first trouble ticket with said plan in place, after the first visit if it is not rectified (then, and only then) would I use these two resources:

If you're on twitter, tweet them at https://twitter.com/comcastcares. They actually are widely known for being a company that has a reputation for not exactly great customer service/interaction, but were ahead of the curve on really really breaking out the big guns to help fix issues that people tweet them with. In part probably people tweeting them back "hey thanks for fixing my cable, comcast!" is amazing PR.

Second, their direct email to a weird kind of customer service triage unit (that has more capabilities and their fingertips than you would ever get going up the normal chain) is We_Can_Help@cable.comcast.com

I definitely used both of those avenues when my digital voice was crapping out all the time and they responded with multiple rolls of 2-3 trucks with 2-3+ techs per visit.

hth