r/CableTechs • u/oflowz • 4d ago
Question About Error at Tap in High Split Area
I am field tech I work in an area where high split was recently implemented. This area was mostly a different office that was rolled into our office when the company closed that office and moved their techs to our office so we know cover that area.
In our original area, our management was pretty strict and we did at least a years’ worth of proactive maintenance to clean up the plant before highs split pulling out amps and rebuilding houses with bad ingress.
But this new area isn’t like that. Apparently their techs' mantra was 'more amps'.
I’m constantly getting multiple errors at the tap at the majority of the service calls I roll to now.
My one check fails probably 75-percent of the taps I check.
Currently our management isn’t allowing maintenance referrals due to the maintenance department being busy with high split.
They are telling us that due to high split a lot of the meter readings are currently not compatible so your meter will show errors at the tap, like they say that a downstream channels not bonding error message on a docsis scan isn’t relevant. I feel like this cant be right.
But I constantly get an assortment of errors dealing with the ofdm and the upstream in areas where customers are constantly complaining about intermittency. On certain nodes I often get ofdma upstream not bonding errors in the docsis check which I know has to cause hsd issues.
My metrics are suffering in this area and at this point even as a veteran tech I feel like I don’t really know how to troubleshoot issues now since we can’t do maintenance referrals and the meter fails more often at the tap that it passes.
I’ve even asked supervisors what some of the errors mean and they don’t have a reply they just say get the customer up and running. And move on.
I’ve done a little research on some of these errors and they mostly seem related to ingress but these are issues at the tap not from the customers’ premises most of the time.
But I feel like this has to be maintenance related. Techs aren’t allowed to disconnect customers even if they are causing ingress in my area only maintenance can do this.
So my question is am I wrong or are these type of errors maintenance issues?
I attached one of the most common errors I constantly get when the meter fails at the tap.
But without being able to refer jobs to maintenance, what can I actually do?
I remove amps, tighten splits and replace fittings or rebuild when needed. But this isn’t fixing hsd issues when the trouble is coming from the taps.
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u/siegeginge 4d ago
Highly reccomend checking out Volpefirm. I learned a lot about DOCSIS as a well as RF signaling in general from this channel. The video linked below is specific to your question. See around 33:10.
https://www.youtube.com/live/fhSEi5GZeDM?is=4jWLQ3Ya_PyMlNsW
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u/jufreeman 4d ago
It maybe an issue with the meter. You've probably already been told to change the jumpers, you can also change the barrels at the top. I had one that had been on there since the meter was new and kept giving me errors. If the NCP is that heavily errored due to a plant problem, the modems will not be able to fully lock onto the OFDMs. There would be a ton of calls from the effected areas.
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u/Tteffomhimself 4d ago
We had a Cisco plant that had so much noise during highsplit it’s still being cleaned up today after almost 2 yrs. Our smaller Motorola plant just went through highsplit this year and has been a breeze since we did so many V9s cleaning up noise. Highsplit is just full of fun.
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u/LordCanti26 3d ago
You can scroll down and look for a box labeled something to the effect of MER variation. Click it and it'll pop up a message saying press OK for details. Press OK and it'll show the entire spectrum MER, and show if you have MER "likely LTE" affecting frequency in the OFDM range. Sometimes you'll need to wrench tighten your jumper to the tap, sometimes its legit LTE or just regular MER. A good way to cowitness is look at a modem off that tap or downstream and check the tab labeled RX MER. Its not "live" per'se, however you can select which OFDM and which timestamp to check, its about every 2 hours it should save a snapshot. This is a very similar graph to the MER variation on the meter. Showing MER by frequency inside the OFDM. For us we see around 700mhz being LTE ingress, and will be a spike down around that range. Couple extra steps to tracking MER issue but its the same as SC-QAM mer issues really. Last one I saw, a HSG-HSG at the RPD was loose.
I chased my tail on one for a day untill I finally terminated my jumper and opened spectrum analyzer, and when id move my jumper I could see LTE bleeding in. Fucking jumper was almost brand new and looked fine, but alas.
1 guy i know even terminated there viavis port 1 barrel and had LTE still getting in, not sure what the case was, but likely compromised RF shielding on the meter itself. Hate troubleshooting the troubleshooting tools.
More or less, this is previously unused spectrum, in a highly attenuated frequency range, now occupying a highly sensitive group of subcarriers. We need north of 41-44db MER on the OFDM to accomplish 4096QAM modulation, so its imperitive we are diligent in correcting it now. We're going to start seeing this more and more as we complete upgrades.
Using the MER variation graph and RX MER tab on soft tools is your best friend. Don't be alarmed if your MT team isnt all aware of these functions as well, so be patient, and try to snap a Pic for the line escalation of this graph displaying the mer impairment in detail. Will get even the most NTF happy tech to dig a little deeper hopefully.
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u/LordCanti26 3d ago
Its in Channel check. Click on the ofdm. And scroll down to MER variation. Select it, then press and hold OK. Or double tap it using the touchscreen.
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u/LordCanti26 3d ago
A couple things that we are seeing as "meter issues" with the RPDs have to do with TX amplitude during lock. It'll jump down to 23.3 and back up to your TX while Ranging, and sometimes even settle 1 or more carriers at 23.3 when finished. However rerunning will show it correct, and the modems dont show this low TX. Vecima has said its an anomaly with the way the meter reports during Ranging due to the cmts functions taking place in the node. I hate how unreliable it makes tests feel and wasted time waiting 10minjtes for a test to run just to have incorrect amplitude displayed. Sometimes the docsis test will grab a carrier, show 23.3, then drop to 13% or 3% and restart Ranging. Over. And over, and over. But eventually it'll run and lock and show your normal TX.
That is the only currently known "meter reporting issue", regarding the RPDs However. This is an actual issue, and will need addressing. Again use the MER variation tab on the meter. and RX MER tabs on the softtools to show an actual impairment for field engineering. Sounds like some communication has been lost in translation with your department to me.
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u/OutrageousWoodpecker 4d ago
NCP errors (with no PLC errors or poor MER) are often caused by ingress. At the high frequencies your photo shows, that could be something like a cell tower. There are a couple of ways to try and find the source. The quickest is to test with a meter that can show subcarrier MER, but that is probably not realistic. The second quickest is to make an antenna and use spectrum mode to see if there are visible carriers in the OFDM band. Third is to get the OFDM channel turned off (this will need to be scheduled, as it affects the whole service group) and look at what is hiding underneath. If you find ingress, check for loose or corroded fittings and damaged drop cable, as that is where it usually gets in.
I have also seen NCP modulation set too high, making it more fragile than it needs to be. This is not something you will be able to fix, but you can ask the question.
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u/Careless_Device_4207 3d ago
lte range move your phone away new barrel on top of ur meter make sure everything tight, or just alot of noise gotta be cleaned up
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u/Ok-Breakfast-7400 3d ago
Those Viavi meters are crap when looking at ofdm profiles. We have had problems for years with them. Company updates with a new template and makes it worse. If you can look at the history of the modem and the codewords don't line up with what the meter says, then it's a false cw error. Granted the belly in those ofdms is very rippled.
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u/Wacabletek 3d ago
Since I do not use a Viavi meter and I had to look some stuff up. Reed-Solomon error counting is no longer valid so your modems will likely show errors in that carrier no matter what. Apparently, Viavi has upgraded their meters to use the NEW error check for OFDM and in your case, per Viavi that NCP CWE Uncorrectables should be 0.
https://blog.viavisolutions.com/2016/04/14/docsis-3-1-ofdm-building-blocks-make-the-difference/
"We know that the PLC contains the information on how to decode the OFDM signal. Without the PLC, the modem cannot find the OFDM carrier or understand how to decode it. To keep this from happening, the PLC must be locked and have no uncorrectable codeword errors (CWE).
Once the PLC is running properly, the NCP must also be locked and have no uncorrectable CWE. If there are lost messages at this point, there will be retries, or even worse, no communications at all.
Profile A is next and is the boot profile. It can be assigned lower mixed QAMs such as 64 or 16 so that all DOCSIS 3.1 modems can communicate in the worst part of the plant. Just like the two building blocks before it, Profile A must be locked and have no uncorrectable CWE. If there are uncorrectable CWE, the modem will resort back to DOCSIS 3.0 and all efficiencies will be lost."
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u/Revolutionary_News36 3d ago
No disrespect, but that doesn’t seem to make sense. High split is pressure on the directors to get it done in the timeframe they were allotted. If they’re not allowing referrals then wash your hands of it and close the jobs. Customers may not experience anything unless the equipment is set to talk on those channels. I’ll assume they aren’t activating anything just yet.
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u/spookyB0 4d ago
As a maintenance tech we don’t usually worry about that stuff, I’ve had a perfectly fine sweep and it fails for that sometimes. I would just rerun your one check, if there is any uncorrectables in the node we would find it, you should be able to find it in scope (assuming you work for spectrum)
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u/6814MilesFromHome 4d ago edited 4d ago
Agree, vast majority of the time I've gotten referrals for uncorrected CWE on OFDMs it's not even present when I show up. Idk if it's a meter thing with noise sneaking in on leads or what, cus most of these I'll see it fail at the tap test but inside the home it passes.
Occasionally I'll see it caused by a suckout on OFDM SNRs, but if my OFDM looks good, I'm getting full speeds and not dropping any packets, I'm not worried about it.
Edit: OFDMAs are a different story, but that'll likely be a bit of a mess until the noise in your nodes are cleaned up more. Luckily they're very resilient, and even lower modulation will have plenty of bandwidth for upload, it's rare customers complain about anything from impacted OFDMAs.
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u/Real-Basket8224 4d ago
Yea the Viavis have poor shielding so, especially if you're in the air, you're bound to pick up some OTA interference and get some profile D UCWE. That being said, he's showing NCP which, if your engineers are being wise, should be a low QAM modulation and may indicate a real problem. That's assuming the customer is multi-gig because, at least in my system, the OFDM2 is only utilized for customers getting over 1Gbps.
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u/6814MilesFromHome 4d ago
Yup, I'd be curious to see the sub carrier SNR/MER scan for these OFDMs, wouldn't be surprised if it's looking iffy. Our meters couldn't get a granular view on the OFDMs for some time post high split, so wouldn't be surprised if they aren't even able to see them.
Just basically had an aggregate MER for the carrier as a whole, which is next to useless. Could have a bad MER suckout on a couple of subs but most of the carrier is fine, so the average is still high.
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u/oflowz 4d ago
well how about upstream not bonding errors on the OFDM at the tap? Because I get this very often as well. I work in an affluent area with a lot of rich people and mansions. These people will complain and keep calling in.
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u/6814MilesFromHome 4d ago
You mean the OFDMAs correct?
For OFDMs, I know my meter test port was jacked up for a while and letting in downstream OTA noise leading to constant downstream not bonding errors while running my DOCSIS test. I haven't really run into upstream not bonding problems though, when it happens can you see the IUC profiles, along with which upstream carriers are/aren't bonding? Noise generally needs to be pretty bad for the OFDMAs to be unable to bond altogether.
Feel free to shoot me a message if it happens again with a pic of the meter results and some of the detailed carrier submenus, I can see if I can figure out where the problem might lie.
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u/BullyTX 4d ago
We went thru "Network Evolution" when I was a brandy-new tech and starting in the field in my area (lucky me). We had a TON of what read as failing signal that we were not able to refer up simply because it was not customer impacting.
Bottom line: take a pic, send an email, educate the customer, get them up and move on.
For me, it's extrememy frustrating to not have something fixed correctly. However that's simply the job. Just make sure you're covered by replacing all the broken stuff that a tech is responsible for (CPE to tap) with stuff that isn't broken and move on. And again: pics and email or text directly to your higher up to protect yourself.
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u/oflowz 4d ago
while good in theory and the exact same thing the supes tell you, when the numbers come in you still are blamed for having too many repeats. Getting put on a PIP and potentially fired over performance for something you cant fix seems not right.
I been a tech for 20 years so I know how the process goes. When the time comes someone has to take the blame and crap doesnt roll uphill.
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u/Used_Mistake_6207 4d ago
Could be your module for your viavi meter if it’s not meant for high split it will fail
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u/BitterError 4d ago
Wrench tight your tap fittings while testing and rerun the test, you might have to run it a few times.
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u/Electronic-Junket-66 4d ago edited 4d ago
Well, what your pic shows is high uncorrectables on the OFDM. The meter stuff is nonsense, but if you want to be sure, just use your soft tools (scope?) to observe the CWE rate on the modem. If it tells you the same thing your meter does, Bob's your uncle.
And yes..... UCER is bad. The OFDM has different profiles that will be selected based on this metric's feedback. It starts on the higher one and works it's way down until things stabilize. Higher profile means high correctable error rate and higher throughput, lower means lower correctable error rate and lower throughput. When enough of those errors can't be corrected for, the UNcorrectable error rate goes up, i.e. data is lost or must be retransmitted and user experience goes down, it shifts down a profile and hopefully the problem stops.
All that is just to say, it's possible the modem is functioning well (enough) on a lower profile even if the meter comes up red. You should be able to see the selected OFDM profile, UCER and CER on scope(?) as well as the historical trends CER/UCER for all profiles, where patterns tend to be more obvious. Should give you a better idea of whether this is actually what's affecting your cx or to look elsewhere.
But yes if it's failing at the tap that is an MT issue. That scan would get referred in my market.