Only 1 downstream channel bonded on CM1200

nao
nao Posts: 2 Novice
in Connectivity

I'm using a NETGEAR CM1200 (DOCSIS 3.1). The modem is online and operational, but the Cable Connection page currently shows only:

  • 1 downstream QAM256 channel bonded
  • 2 upstream ATDMA channels bonded
  • 0 downstream OFDM channels
  • 0 upstream OFDMA channels

The downstream channel currently shows:

  • Frequency: 609 MHz
  • Power: +7.1 dBmV
  • SNR: 46 dB
  • Correctables: 0
  • Uncorrectables: 0

Spectrum performed network work in my area on August 30. Since then, I’ve been experiencing frequent intermittent connectivity issues. The connection was generally stable before that work. I don’t know whether the modem was already bonding only one downstream channel before August 30, so I’m not assuming that the current channel configuration was caused by the network work.

Is it normal for the modem to operate with only one bonded downstream QAM256 channel and no downstream OFDM channel, or should it normally be bonding multiple downstream channels and/or an OFDM channel?

Answers

  • RAIST515O
    RAIST515O Posts: 355 Contributor
    edited October 7

    Have seen markets dropping to only 2 upstream 3.0 channels to make room for the new channels. Basically, required part of the spec for fallback and may aslo be used with value plans possibly.

    Some new cut-ins have had weirdness with the OFDM upstream and failed over to those 3.0 channels, but those can still offer up towards 20/40mbps depending how they are configured and how clean things are.

    What raises an eyebrow though is not seeing multiple downstream channels active. You may only see one OFDM lock downstream, but would still be getting a group of 3.0 channels in the mix for failover support.

    May want to double check. The 3.0 channels will usually get ID's 1-32, likely in the neighborhood of 300,000 to 800,000 mhz, with channels being spaced 6mhz apart.

    The status page may be reporting the primary it latched when initializing, but it will also register signal values with those details and enumerate all it finds that can be used.

  • nao
    nao Posts: 2 Novice

    Hi RAIST515O,

    Thanks for the detailed explanation. I really appreciate it!

    I double-checked the CM1200 status page. The single 609 MHz channel isn’t just the primary channel shown under the Startup Procedure. Downstream Bonded Channels has only one entry.

    I also contacted Spectrum support via chat, but they told me that everything looks normal from their side and that a single downstream channel can be considered normal.

    Fortunately, the connection has been stable today. However, the uptime over the past week has been below 80%. If the problem continues, I’m planning to have a Spectrum technician come out in the next few days. I’ll report back here with what they find.

    CleanShot 2026-10-07 at 14.42.27@2x.jpg
  • RAIST515O
    RAIST515O Posts: 355 Contributor

    Yeah... that could become problematic if it is indeed the only channel it is using, as it is only good for a ballpark of 38-40mbps (depending on overhead). So if you are getting more downstream than that, it is using OFDM or additional channels and you just aren't seeing the details.

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