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Power outage require power cycle of UPS-connected cable modem

jeff_cote
jeff_cote Posts: 1 Rookie
in Connectivity

I have an UPS to which my router, my switch, and my cable modem are all connected. We just lost power, and the whole home generator kicked on (as expected), so nothing runs from the UPS for more than ~20 seconds. (It says it can run for ~70 minutes under current load.) The router, and presumably the switch never lost power (it's unmanaged so no logging). My assumption is neither did the cable modem. (Verified it's plugged into a powered socket, not a surge-protected socket on the UPS.) However, every time we lose power, I have to reset the cable modem in order to regain internet access. The cable modem log shows this at the time of the power outage: "Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=xx:xx:xx:xx:xx:xx<redacted>;CMTS-MAC=00:90:f0:25:00:00;CM-QOS=1.1;CM-VER=3.1;" Based on this, it appears as though Upstream scheduling is broken — the CMTS is supposed to periodically grant my modem's specific Service ID (SID) a private "unicast maintenance opportunity" slot to do ranging/keepalive. It's not doing that for my modem specifically, even though it's still broadcasting to everyone. After ~30-40 seconds of not getting its own slot, the modem's T4 timer expires and it's required by the DOCSIS spec to tear down and fully re-initialize (re-scan, re-range, re-register, fresh DHCP). Can I get someone at Spectrum to check if there's a known issue with stale SID state on that CMTS after node power events? Some CMTS software versions have documented bugs with this.
FYI: This is 100% reproducible on every outage.

I'd be happy to supply my address in a private chat if that will help troubleshooting. Thank you in advance!

Best Answer

  • catchtwentytwo
    catchtwentytwo Posts: 216 Contributor
    Answer ✓

    Smaller UPS batteries are commodity items and prone to failure. Most of these batteries have a date of manufacture stamped on their case and two years of service would be stretching it.

    The only true way to test UPS batteries is to fail the input power of your UPS with the modem connected (pull the plug test) to see how long it lasts.

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