DOCIS Upstream Low Powerlevel

[gbeck78]

The powerlevels of my upstream DOCSIS Channels are generally rather low with <40 dBmV. I am also observing modulation fluctuation between 1024QAM and 64QAM for the upstream DOCSIS 3.1 channel multiple times throughout the day.

Question is:

• Should I be concerned about this as this does not seem to affect the performance of the connection unless the upstream 3.1 channel is lost completely and latency starts to generally increase? Does it justify a complaint?
• docsight reports elevated levels and seems not to differentiate between levels falling below the threshold window of 50-54 dBmV and exceeding the window. I would consider this a bug/enancement request for the tool?

[itsDNNS]

Thanks for the detailed report and screenshots!

Regarding point 2 (the DOCSight behavior): You are absolutely right, and this is a valid bug. The analysis code checks whether the upstream power falls outside the acceptable window (e.g. 41-47 dBmV for the warning tier), but the labels always say "elevated" or "critically high" regardless of direction. In your case the levels are below the window, so reporting them as "elevated" is clearly misleading. I will open an issue to track this. The fix should differentiate between "too low" and "too high" so the messaging actually reflects what is going on.

Regarding point 1 (whether to be concerned): To be honest, we are not really the right people to give you a reliable answer here. We are users ourselves who bundled our cobbled-together monitoring setup into a more polished solution and made it available so others can keep an eye on their line too. The modulation drops from 1024QAM to 64QAM on the DOCSIS 3.1 upstream channel do suggest that something is not quite right on the line, and values consistently below 40 dBmV are on the lower end. But whether that justifies a complaint depends on a lot of factors (house wiring, splitter setup, node utilization, etc.) that we simply cannot assess from here.

If you want a well-informed opinion from people who deal with these kinds of signal issues regularly, I would recommend posting the exact same question with the same screenshots over at kabeluser.de or Vodafone Kabelforum. Kabeluser in particular seems quite active and has folks who really know their way around DOCSIS signal analysis.

[itsDNNS]

Opened #99 to track this and already shipped the fix in d221afc. The analyzer now differentiates between upstream power being too low vs too high, so the labels should accurately reflect what is going on from the next release onwards.