First, a quick explanation.
- Upstream power: should be between 40 and 50 dBmV. Whenever this value gets out of range it's usually by going above 50, which means the modem is pumping too much power attempting to compensate for a bad connection.
- Downstream power: should be between -10 and 10 dBmV, and ideally 0, which would mean the signal is received with the same exact strength it is transmitted by your ISP. If nonzero, it's better for it to be positive rather than negative.
- SNR a.k.a. signal-to-noise ratio: should be 35 dB at least. Since this is a ratio, it has no upper limit, and the higher the better.
(Note that these hints assume DOCSIS 3.x and the modulations displayed in the screenshot)
- Unerrored codewords: data that was received without problems.
- Corrected codewords: data that got corrupted in transit, but was fixed by Forward Error Correction. Less severe than the ones below, but you'll still want them to be as close to zero as possible.
- Uncorrectable codewords: same as above, but couldn't be fixed. You want these to be as close to zero as possible. If you get thousands of these on one or more channels, you have interference or bad wiring along the way.
As you can see, my levels are pretty good, but I've heard of people getting perfect zeros on their downstream power, or SNRs in the low 50s, so I thought it'd be fun to compare.
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