For the past week I've had serious internet issues where people couldn't use my services because of packet loss and upload speeds plummeting to kbit/s resolution (0.09 mbit/s).

I noted that one of my Upstream frequency was at 39600000 hz even after leaving my modem unplugged for a long time and the channel was reporting 1.280 Msym/sec.

Finally a service man comes out and runs diagnostics and says everything looks fine, I go and check my modem is the Upstream channel has now changed to 16400000 hz and 5.120 Msym/sec and everything is working perfectly fine again.

So my question is how are the frequencies assigned? Does the central hub say "Talk to me on X Mhz" and the modem abides by that?

I honestly haven't a clue and my only deduction was that there was too much noise on that frequency and when he ran diagnostics it told central poor communication on X Mhz and switched?

  • Unfortunately, questions about networks you do not directly control are off-topic here. You need to ask your ISP about that.
    – Ron Maupin
    Oct 30, 2020 at 11:25

1 Answer 1


Your cable modem receives configuration from the CMTS network. Generally, this is provisioned in their system based on your subscriber MAC address. That's why you have to let them know when you buy a new cable modem, for example.

Your problem was most likely caused by the cable company mistakenly re-provisioning your modem as a VOIP terminal instead of an Internet customer modem. Speculating, the low data-rate wasn't the result of poor RF on the upstream channel; it's because they assign ~96Kb/s (or so) for the CPE used by their phone service, and put those CPE onto DOCSIS channels with a legacy configuration that is backwards-compatible with much older equipment to avoid having to upgrade old VOIP CPE.

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