In context, the upstream power levels need to be 34 dBmV on the upstream, and ideally in the 38-48 range. For FTTP that can go down (IIRC) to 27 dBmV.
The full range of numbers aren't formally admitted by VM, and the full list of things I look for would take me half an hour or more to type out. VM staff rely on some shonky diagnostics that usually work but sometimes miss stuff, the amateurs like me rely on some word of mouth advisories plus observation and experience. This sometimes leads to differences of opinion, but they usually get sorted out. It's difficult to be particularly precise about the numbers because DOCSIS (the technology underlying cable internet) is an ageing analogue technology, and has a Heath-Robinson complexity, so what we look for is an actual problem, and the indicators in the numbers that point to the likely source of the trouble - and that can be upstream and downstream power (both magnitude and range across channels, SNR, modulation levels, error counts, timeouts, network log messages. Often we look for a conjunction of indicators rather than just a single value that's wrong.
