Some minimal background for context, I work 3rd shift weekend providing customer support for an operating system vendor.  This means that I get to (try to) live through any ISP changes that xFinity/Comcast throws on their victims.  About a month ago some change was made and my SB8200 that had been working fine (with a functioning DOCSIS 3.1 indication), so to speak.  Performance went to heck and none of the troubleshooting suggestions helped (rebooted several times, factory reset, etc).  At the time the modem log had an entry about a failed firmware download and most of the channels had logged both correctable and non-correctable errors.  It should have been a hint that the normal address for the SB8200 config pages didn’t respond but 192.168.0.1 connected.

Enter Comcast…  After the usual foolishness the agent finally tried to ‘look at’ the modem using their tools and that was a total failure.  From my view the modem was working but, honestly, wasn’t performing as well as internet over dial-up or DSL.  Appt with a tech scheduled (or, aka “truck roll”) and in just a couple days.  Again, the usual stuff.  There’s a problem with my DMARC, my “interface/NAT box” on the house and everything from the PoE filter “in” was unusable.  The same collection of electronic giblets that had been working exceptionally until whatever change they tried to pump down the pipe.  Tech removes ALL the nasty “unsupported” hardware (an amp/mux, several splitters that were “wrong.”  Still having trouble so we escalate to one of the “curb” guys because there’s a problem there.

Their second guy shows up and makes some magical changes to our interface to the BIG “pipe” running through the ‘hood.  That interface had multiple “drops” which were unterminated and he fixed those.  Gonna be ALL better now!  When I invited him to come look at the modem status and logfile he “hasn’t looked at modems for years and wouldn’t know what to check.”  Still running at about 20%.  I rebooted and reset to factory, again, with no improvement.  The phone agents still claim that they can’t “touch” my modem so a return visit gets scheduled.  I did some more testing and bought a NEW SB8200 (the previous one was used, from e*bay and had worked FINE for quite a while so it seemed possible that it wasn’t working properly).

Tech 3 (an inside tech) shows up.  He reviews all the pieces-parts to be sure they’re compliant and blessed by xFinity.  Spends most of the visit on the phone, checks the main feed from the street, the signals at the box and where my modem lives.  The new SB8200 still will NOT connect at DOCSIS 3.1 levels.  Tech 3 starts with the “SB8200s they never work for me, etc” and it’ll ALL be better if I get one of their rented units (which by this time many of them are “refurbished” anyway).  He makes a couple more calls and returns with the statement that I should just stop complaining because “our area” hasn’t been upgraded yet to support DOCSIS 3.1?  I will admit that our geography was originally serviced by Adelphia but Comcast bought them years ago.  I’d think that, by now, they’d have gotten around to having most of our area working at DOCSIS 3.1 (when they’ve been in the press for several months about pushing DOCSIS 4.0 out).

I finally poked and prodded one of my lesser used systems to have the same subnet as the SB8200 expected and have logged in.  On the “status” page there are several comments that are alarming.  Under both the “Connectivity State” and “Boot State” the status is “OK” but the comment for both is “Partial Service (DS only).”  The modem has been “provisioned,” both times I spoke with a real human (I didn’t succumb to their whining that I could do everything through some “app,” call me old fashioned like that).

Does this seem, in any way, legitimate?  I’m still puzzled how I had a SB8200 (used) that WAS showing that it had made a DOCSIS 3.1 connection and it seemed faster.  I would expect that a newer  version of the same modem should, at least, work at least as well.  The channel signals do not seem optimal and all are showing errors, both correctable and not.  The frequencies listed seem unusual at best.  All but one are showing 256QAM modulation and that one is OFDM PLC at frequency 690000000Hz, -7dBmV, 37dB signal-to-noise with 160 million correctable and 2.3million uncorrectable errors.  I doubt that a random new SB8200 is the source or cause of this problem but I need something a little more than “my word” to get xFinity to even consider that they still have an issue.  If needed I’ll find a way to get screen scrapes from the modem management pages if that could help.

MrVXT