Hey thanks I didn't realize I could do that. Updated the article with the docsis log.

Bunch of

UCD invalid or channel unusable and SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing

ddtaylor 7 hours ago | parent | next [-]

What used to be very useful was to get the signal to noise ratio. When I had problems it was because they had installed amplifiers at various parts of the line and it eventually added up to a problem with amplifying too much noise.

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razingeden 6 hours ago | parent | prev [-]

gotta ask, just because i went through this with spectrum recently.

have you grabbed an extension cord and tried connecting the modem outside at the drop for awhile?

i hear you that your neighbor has the same issue. but if youre in. say a development by the same builder, or were all part of a comcast upgrade at roughly the same time ..

and well… you both recently upgraded to 1.2(?) because that would be the latter case

after my gig upgrade and a few tech visits i ended up finding a splitter that only goes up to 800mhz or so (if that) inside a wallplate.

TLDR:

you might have a 5-1000mhz splitter. thats widely used by comcast still.

OFDM is 1008mhz or so and you wouldnt notice the problem under, or maybe just UP TO gigabyte speeds (eg: downgrading to 500mb might mysteriously “fix” it).

but you WILL notice this at 1.2gb.

spectrum is future proofing and using 5-2500mhz splitters

ANECODTAL:

my modem locked with the 800mhz splitter, but it dropped , cycled and had horrible upload speeds.

techs never tried or thought of this . the final boss tech took photos and even took the splitter back to show his boss. i guess multiple units had tickets after the gig upgrade and they had an “aha” moment.

TECHNICAL:

i would expect something more like multiplexing errors in this situation. forgive me because im 20 years out of the game (was an RF/install tech on analog CATV , and cable modems when those were brand new to Charter) and had to look it up but i think docsis 3.1 is dependent on 957–1151 MHz or 1008–1152 MHz

its that 1008+mhz where now your splitter is acting like a 5-1000mhz filter.

its not perfect like okay maybe 4-1003mhz gets through the filter maybe even more permissive if its a cheap one. but thats NOT a clean signal for that frequency band its more like bleed-through.

sort of similar to traps (the little barrels theyd screw onto your line to block you from getting pay channels in the olden days) and how you STILL could sort of see and hear. a little bit of what was going on on cinemax at 3am and at least get the IDEA. :>

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vedmed 5 hours ago | parent | next [-]

I had an old 15+ year old line when I moved in. Helped my neighbor cut a few hundred of his monthly by getting xfinity and they ran a brand new drop for him. Then just recently they "upgraded" my line. But I don't have any splitter or filter its just a connector with a ground that attaches my home cable to the drop cable.

	▲	razingeden 4 hours ago \| parent [-]
		the reason id suggested connecting your modem at the outside drop would also cover any and all inside wiring issues. and that could be anything. frayed end. a nail through it. moisture. i think my inside wiring was done no earlier than 1991 , but maybe redone once since then and it looked pretty good but i found this on the back of a wallplate , just yesterday: https://ibb.co/5XjkJ57J - expires in 6 months the easiest thing to do is check it at the box and then if nothing else thats ammo for dealing with customer service “look, i connected at the drop and have the same issue its NOT my inside wiring.” everything from that point back is their problem and they owe you bill credits until its fixed, so get the proof and go back with it. in my case my modem worked perfectly at the drop :D so i unfortunately had some digging to do its not practical to suggest someone on the internet go ripping open all their wall plates and checking every inch of inside wire or maybe even running a new one. unless it passes the drop test, and then yeah, thats what needs to be done. but plugging into the drop will 100% prove whose problem this is. youre california so thats also good ammo for a PUC complaint, that you did that and proved its not your inside wiring and now theyre refusing to deal with it. maybe that will get it to the right person on comcasts end faster when they review it.

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toast0 5 hours ago | parent | prev [-]

This seems pretty likely, but shouldn't a tech roll have included sampling the signal strength/snr at these frequencies? Or would the tech tools be likely to be on old frequencies too?

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razingeden 5 hours ago | parent [-]

the SNR and the lock would be perfect at the drop using tech meter.

or, plugging your modem into your dmarc/outside box for a little bit would also confirm or deny this

	▲	toast0 4 hours ago \| parent [-]
		Tech should plug the meter into where the modem is too, though, right? And if the SNR looks good at the dmarc and not at the modem, there's your problem... Tech can peace out if you don't have inside line coverage.