Our good old Cisco UBR-7223 is experiencing a very strange problem:
There are two modem cards installed (MC-11 and MC14C). From time to time (no pattern, sometimes twice in an hour, sometimes once in a week) all the modems on the MC14C card would go offline and will show a receive power at the uBR side of -20, -30 and below dBm.
All the upstreams to the MC14C are also combined and go to the MC11, which operates fine at the same times, thus eliminating suggestions about RF plant issues (noise, power, etc.)
Also, rebooting the uBR solves the problem immediately (just to have it reappear in again a random time), but still I haven't managed to solve the problem without rebooting it. Clearing or shutting down the relevant interface doesn't help. We've driven down the modulation back to QPSK - it changes nothing.
These problems are appearing from about half an year, and are becoming more frequent rapidly to the level where customer disgrace is getting higher. The problem have no obvious connection whatsoever with the number of modems online, the ammount of traffic going through the uBR or something else. The uBR is collocated in a constant-temperature UPS-powered colo, so it couldn't be environment problem too.
I'm currently searching for a replacement card to try and see if it's the card itself. Meanwhile - anyone any suggestiongs at what might I look at to debug this problem (if there's any chance it's not a hardware one)?