Welcome to the Spectrum Community

Get answers, share solutions, help your community.

Start here

Netgear CM1200 modem dropping internet, random lagging in games

echao12echao12 Posts: 3 ✭✭
edited August 27 in Connectivity Aug 27, 2020

I originally had an Arris SB6183 that was working fine until it died after a lightning storm. I pulled out my old Arris SB6141 to replace it temporarily. The SB6141 also worked fine for the past few months with the exception that I was only getting ~300Mbps on my 400Mbps plan (this is expected as it only has 8x4 channels).

A couple days ago, I replaced it with the Netgear CM1200. Internet works fine for a while until it randomly slows down (very noticeable in games) and sometimes drops connection several times a day, and then recovers without rebooting. All lights on the modem are solid green, except for the upload light which is constantly blinking green (indicates cable modem is scanning for an upstream channel). When the internet is working, speedtest.net shows ~470Mbps down/~22Mbps up, and ping ~20ms. Also, I am not using LAG/port aggregation.

Anyone else having issues with the CM1200? Should I try to get a technician out, or return the CM1200 and try out the Arris SB8200? I'll probably switch back to the SB6141 later today or tomorrow.


Best Answer

  • echao12echao12 Posts: 3 ✭✭
    Aug 29, 2020 Accepted Answer

    Yesterday evening I decided to buy the Arris SB8200 from my local store and got it activated. Internet has been fine the whole day, and no lagging in games.

    Looks like I will be returning the CM1200. I wish I could do some more diagnosing to find out the issue, but not having stable internet is quite annoying to everyone in the household.

    I will say I suspect that it was an upload issue. Most posts I've seen about the CM1200 do not have an OFDMA upstream channel locked. The lagging/disconnects occurred when there was a spike in upload activity on my router's graphs. There was also an odd situation where in Discord voice chat I could hear everyone perfectly fine, but my friends said that my voice was delayed by several seconds and I sounded robotic. Maybe the Spectrum approved firmware version V1.02.01 still has bugs with OFDMA that is fixed in the latest version V2.02.05.

    @RAIST5150 - 3.1 modems are indeed overkill for my plan, but the SB6183 lasted me over 5 years so I don't mind paying a little extra to future-proof. I also didn't want to risk Spectrum giving me a modem with an Intel Puma 6 chipset. My router is a Ubiquiti UDM-Pro, so I think I've already spent enough money there 🤑

Replies

  • misterjmisterj Posts: 80 ✭✭✭✭
    edited August 28 Aug 27, 2020

    echao12, please look at this thread:

    This looks like the same problem as yours with a CM1000. I will check back to see what you think. Looks like a bad provisioning by Spectrum to me. Thanks and enjoy, John.

    EDIT: I suspect if you can talk Spectrum into correcting your provisioning then there will be no need to talk of replacing any HW. I have a SB8200 in my plans due to Spectrum not allowing me to login to my Ubee equivalent. BTW Arris has a Certified Refurbished one available now for $130.

    Great screenshots!

  • RAIST5150RAIST5150 Posts: 794 ✭✭✭✭
    edited August 28 Aug 27, 2020

    @echao12

    The line has the appearance of being "boosted" somehow... Downstream is higher than normal and upstream is staying lower than normal (modem will increase upstream power if headend is not getting good signal).

    This could pose issues for various reasons... one being any noise on the line also gets boosted with it.

    Guessing this is also happening if wired directly into the modem?

    May want to verify that before calling anything in if you haven't... especially since it is your own hardware--rule out potential router specific issues.

    Not sure how long the CM1200 has been on the approved list. I recall there were some issues at the gig tier when they first introduced some new models to that list a while back--may still be a bit touchy.

    May be worth putting the 6141 back on there for a comparison, at least for the channels you can compare statistics on.... just to see if the pattern persists. Would certainly warrant a trouble call if the signaling doesn't stabilise with the Arris/Motorola in play.

    As for whether to return the CM1200... guess that depends? Do you need all the CM1200 extras if you are staying on the 400mb tier? Even if you are looking at going to the gig tier... may still be "overkill"? IDK if Spectrum will be doing much for aggregating on gig anytime soon and all that. Just wondering if there is some special use case for needing specific features of the CM1200. I am guessing you have a good router that still meets your needs? If not, maybe spend the upgrade money there?

    Just thinking... since you are using the separate modem and router set up, you have the option to bring in a Spectrum modem. They don't charge a modem rental fee on the Spectrum plans, just a wifi management fee if you use their routers. Support upside is it would be their hardware on the coax now, not yours.

    Once you are satisfied with the line performance with their modem and all, then you could look into where to upgrade--the modem or your router.

  • misterjmisterj Posts: 80 ✭✭✭✭
    Aug 28, 2020

    echao12, I have seen at least three of your same type problems. I suggest you do two things. Contact Spectrum support and report that your modem has two complete connections, one DOCSIS 3.0 and one 3.1. These are using 384 MHz of spectrum. Also please contact CM1200 Support and discuss it with them. Please let us know your results. Thanks and enjoy, John.

  • RAIST5150RAIST5150 Posts: 794 ✭✭✭✭
    edited August 28 Aug 28, 2020

    3.0 and 3.1 can coexist... kinda has to with the age of the infrastructure still in play. The cm and cmts negotiate which ones to support.

    The likely problem here is a more typical scenario... how the quality of signal is deviating from this system's historical norms, causing too much data corruption.

    More often than not, the bulk of problems here persist because of signal quality issues and/or utilization levels

    @echao12 ,

    I missed this last night, but your modem is latching primary channel on one that is getting flooded with corrupt packets. The Netgear firmwares have a nice troubleshooting tweak, but I do not want to post it openly as I am unclear on Spectrum's stance on having such discussions openly in the forum. Will see if I can reach out in PM about that to see if we can test against this issue so you can notify support about the findings if it provides a workaround for you. Don't worry, it is quick and easy to both setup and reset to normal operation.

  • RAIST5150RAIST5150 Posts: 794 ✭✭✭✭
    Aug 28, 2020

    @echao12 ,

    Private message sent. If you click on the account button in the upper right corner of the page to access your profile, you can check the message with the envelope icon. Hope it helps!

  • echao12echao12 Posts: 3 ✭✭
    Aug 29, 2020

    If you're curious, here is the signals on the SB8200. I added a 9dB forward path attenuator (FPA9-54) to bring the downstream power closer to 0dBmV. I had tried the same attenuator with the CM1200, but it didn't affect lagging/disconnects. Otherwise, the frequency, SNR, and upstream numbers look pretty similar to what the CM1200 was reporting.


  • RAIST5150RAIST5150 Posts: 794 ✭✭✭✭
    edited August 29 Aug 29, 2020

    @echao12

    Been reluctant to go to 32 channels yet because the channels aren't really consistently clear in our market yet. The growing pains are pretty bad here... way too many homes have RG59 in the walls, and convincing them to run fresh RG6 is like arguing with a brick wall. Poor guy didn't how to act at my last house when I asked him if he had a bit long enough to just drill clean through the outer wall to run the modem line right into the office... no one ever let him do that direct of a run before.

    Downstream is our pitfall. 16 channels is kinda the sweet spot atm... gives us room to breath and rethunk the odd channels that want to flake out on the hotter days. Sometimes channel 1 and/or 32 will just go AWOL on people, so can still run into issues with even a 24 channel model. IDK how these guys keep it together with all the calls they get here.

    Kudos on that Ubiquiti setup. Serious stuff there. Running at that level, you may one day want to actually look into aggregating LAN side against the gig plan. Seen some guys reporting they were actually able to consistently pull 1.2g off the coax that way in some markets.

    Once toyed with the idea of a managed switch. Looks like we will be stuck at the 100mb tier for a while. But now that my daughter started the career track and is out on her own, I only have to compete with my mom doing the occasional Hulu stream. So far the old Asus's QoS manages to keep her Roku's in check well enough. I hear QoS is much better on the newer models since they can use the new Merlin builds, so may windup going that route instead.

    Good luck out there.

    Edit: nvm... missed the extra post about you preemptively padding the line yourself. Nice that you were able to get it stable with the 9... gives you room to move if it flakes again. But WTH is going on at 267mhz??!! If it gets too out of hand with the winter/summer shifts, might be worth running it up the flagpole with maintenance for an upstream retune... never know if they will be open to it.

  • misterjmisterj Posts: 80 ✭✭✭✭
    edited August 29 Aug 29, 2020

    echao12, I talked to Arris support yesterday and was told that DOCSIS 3.0 and 3.1 should not have simultaneous connections. When looking for best performance the modem will switch between the two and maybe that is what we are seeing. Arris is very nice to talk to me even though I do not use one of their products right now. Support is available 24/7 and glad to hear from customers. I suggest you provide the screenshot you posted above plus any "Downstream OFDM Channels" screenshot you can create (here too, please). I do not know what is going on, but between Spectrum and Arris I think they can determine and correct it. Your levels look great, up and down. I like a little more signal, so I would not have added the attenuation. Before I went blind on my new modem, my old Technicolor Modem/Router ran consistently 6 bBmV to 10 dBmV, the specification is -15 to +15 dBmV. I will step back now, but if you think I can be of any help, please address me by name - always glad to try to help. Thanks and enjoy, John.


    EDIT: BTW, 267MHz is part of the OFDM channel.

  • RAIST5150RAIST5150 Posts: 794 ✭✭✭✭
    Aug 29, 2020

    Again, have to take everything in the proper context of how this system has typically behaved.

    Downstream at the modem is actually now in a sweet spot that they like to see when practical, especially in the summertime... likely why the OP opted to use a specific type of pad... drop 8-9 on one side while only risking roughly 1 on the other, as opposed to heavily impacting both directions.

    3.0 and 3.1 can coexist just fine... it is even baked into the specification. It pretty much has to with the age of the infrastructure in place... as they bring in upgrades, the 3.1 features can be integrated more and more. They have been running like this "mixed mode" for a while now. As mentioned before, the cm and cmts will negotiate which to use for what.

    The concern about the 267mhz channel wasn't about what it is... it was about the absurdly high error rate it is having to correct.

Sign In or Register to comment.