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koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23
reply to koitsu

Re: What to do about 11 weeks of node/network problems?

Been a few weeks since my previous update -- keeping it short this time. Things are still continuing to be investigated (maint/line techs have been out twice in the past 48 hours, for example) and still working on narrowing down what section of cable or devices are susceptible to interference in the 747MHz and above freq. range.

One key point I thought I'd mention: putting me on a "direct line" or "ground line" did not alleviate the issue, meaning the interference is presumably coming in somewhere along Church Street (two spots are being focused on at this time).

I've kept in very close contact with the Network Engineering Supervisor during all of this -- in fact, he's who I mainly communicate with when giving updates/information.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

1 recommendation

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Strange things are afoot at the Circle K! Today a couple trucks from CableCom were out working along Church Street (particularly at the Hope/Church intersection) with a very large spool of cable (not pictured).

I'll have to ask my Comcast contact what was done, but my initial guess is a new set of cable has been run, meaning the existing cable may have degraded/been damaged in some way (identical to that in San Carlos some time ago (reference)). Comcast maint/line techs were out here yesterday for 10-12 hours straight, spending their time along the section of Church Street (map).

I imagine there will be some lengthy downtime in the morning sometime within the next week or so as Comcast switches over to the new cable run, but that's perfectly fine by me assuming it solves the issue.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

1 edit
Yesterday (01/04) morning I lost sync and used the opportunity to run an errand. Both Comcast line/maint techs were out tinkering with the cable which CableCom had installed the day prior, so I had an opportunity to chat with them.

The techs spent a lot of time at very early hours (5-6am) on 01/02 narrowing down exactly where the interference was seeping in. Doing this required placement of terminators on the main cable run each step of the way (starting at behind our building, then down to the spot on Church Street where the cable heads south-east, and so on), then examining the SNR with an analyser. Time consuming but it's what it took.

They found that the interference was being introduced in the stretch of cable between the spot behind our building and Church Street (see map -- referring to the blue line that goes from behind my building heading north-east, where it intersects with Church Street, before going south-east). The cable had no visual anomalies (e.g. no deep gnaw marks from our aggro squirrels ), but was definitely bad in some way. They've taken the cable and will be using it for "educational purposes" + doing further analysis on it using a TDR. The cable was also encompassed by all sorts of tree branches (the trees are on private property; the guy who owns the house next to our building really needs to have someone out to prune them. They're a good 5 or 6 years overdue).

The tech doing most of the analyser work said that with his analyser hooked up and with the terminators in place, on that cable segment, he could see SNR fluctuate badly for the 747 and 753MHz range, jumping around constantly between roughly -28dB and -39dB. "It was all over the place; it shouldn't be like that".

During the troubleshooting process, the techs also found that the cable between that point at Church Street, and the Hope/Church intersection, was also damaged (this time visibly so). This cable was not the source of the interference seepage, but the techs told me that they preemptively had CableCom run a new cable for that as well, because "in 1-2 years the cable would have degraded to the point where the interference issue would have recurred". The root cause of damage to that cable seems to be the (city-owned) trees along the street; they didn't go into details.

On the morning of 01/04 they switched everything over to use the new cables.

Lo and behold, my SNR on all frequencies is now 37dB and steady. With their analyser it shows something like -35 with little to no variance. On my end, there's no variance at all -- it's absolutely rock solid and that's quite apparent in my SNR graphs. In fact, the occasional +/-1dB I'd been seeing on some of the other frequencies too are now also gone.

Rephrased: since the cable replacement, my connection has been rock solid; Youtube videos load quickly, I'm not seeing massively incrementing uncorrected error counts, and no longer do I see packet loss.

The techs and I both agree there is a huge improvement since the cable replacements, but also agree that we should revisit things in some weeks (maybe 4-6 weeks). They'll also use that opportunity to get rid of the "ground line" and put me back on the same splitter/hub as my neighbours (i.e. reverting back to the original cable configuration prior to the work done on 12/19). I also get to discuss with appropriate managers the possibility of service credits.

It's evening time here, but tomorrow I'll go out with my camera and record a short video showing the general vicinity/area of where the cables were replaced.

So assuming the cable replacement fixes the issue: from start to finish, the entire ordeal lasted from roughly August 10th 2012 until January 4th 2013. That's almost 5 months.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.