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Getting a max of 4 upstream channels on an 8 channel modem; is this normal?

remeikaremeika Posts: 4
in Connectivity May 10, 2020



Today I upgraded to a 24x8 channel DOCSIS 3.0 modem (The Motorola MB7621), from the 16x4 channel modem supplied by Spectrum. Once the modem was activated, it bonded to all 24 downstream channels (yay!), but only 4 upstream channels, out of the 8 available on my modem. Screen shot of the channel statistics attached.


I'm wondering, is 4 upstream channels a limitation of Spectrum's network in Brooklyn, NY, or should I bug tech support about this? My service level is Spectrum Internet Ultra 400/20 if that helps.



JamesScreen Shot 2020-05-09 at 8.47.53 PM.png

Best Answer

  • Smith6612Smith6612 Posts: 44
    May 10, 2020 Accepted Answer

    Most if not all of Spectrum's cable systems are only running a 4 channel upstream configuration. Mid-split or High-Split (physical plant) upgrades will be required. So it should be considered normal to only see four channels.


  • remeikaremeika Posts: 4
    May 10, 2020

    Thanks, that makes sense. I guess I'll set a reminder to check the modem in 6 months and see if a plant upgrade has happend!

  • karlbeckmankarlbeckman Posts: 2,206 ✭✭✭✭
    May 10, 2020

    Since your UPLOAD speed is only 20 Mbps, four uplink channels are more than sufficient.  There is no reason to expect any future increase in the number of upstream channels to eight or beyond.  The cost to deploy a plant upgrade of that magnitude across the NYC area would be many millions of dollars, which is a lot more than the incremental revenue from customer billings on the 400/20 Mbps service tier. 

  • remeikaremeika Posts: 4
    May 10, 2020

    Was definitely not expecting a speed increase by purchasing a wider modem. I have some vague hope that by spreading across more channels, the new modem will be more resistant to local network congestion, and be able to sustain my max plan bandwidth more consistently. An if even that is not based in reality, at least the new modem has better looking indicator lights! 😄💸

  • RAIST5150RAIST5150 Posts: 642 ✭✭✭✭
    May 10, 2020
    Each upstream channel is technically capable of up to around 27mbps throughput.

    So it will be a while before you would need more than 4 upstream channels.
  • remeikaremeika Posts: 4
    May 24, 2020

    Thought I'd follow up about the behavior of the 24-channel modem after 2 weeks on the Spectrum network in Brooklyn, NY. Short version: getting a modem with more than 16 downstream channels does not seem worth it!


    Here is a chart showing the number of corrected/uncorrected errors per channel after about 2 weeks online. The 8 "extra" channels I bought by upgrading my modem have way more uncorrected errors than the lower channels. It looks like the network near me is just not tuned to perform well on these.

    Screen Shot 2020-05-24 at 7.02.47 PM.png


    That said, the SNR is much better on those channels. I suppose this makes sense if Spectrum is only handing out 16 channel modems, and mine is basically alone communicating on them.

    Much better SNR above channel 16Much better SNR above channel 16


    You can download the dataset from my modem here.

  • Smith6612Smith6612 Posts: 44
    Jun 04, 2020

    Some of the higher frequencies in the 700-850Mhz range are prone to interference by LTE. If there is plant leakage or a less than optimal shield/connection somewhere, you'll get errors on those. Lower frequencies below 700Mhz can also be a bit more error prone for the same reason, but also due to devices, whether faulty or improper, being installed in their homes on the same cable system.


    It's worth noting that the lower frequencies are usually prone to more noise. Bring those errors to Spectrum's attention, though. They probably need plant maintenance to check for ingress.

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