# Meaning of RCA DCM425 Cable Modem Diagnostic Statistics

My home internet connection is provided via a DOCSIS 2.0 complaint RCA/Thomson DCM425 cable modem. As far as I can tell the DCM425 is an un-managed device, but it does provide a web interface for viewing diagnostic information.

This all means something to my ISP, but I don't know much about DOCSIS. Some of these I can figure out via context such as SNR for Signal to Noise ratio. However, I would really like to know more about what these diagnostics refer to.

Can anyone explain 1) what these various pieces of diagnostics information are or refer to and 2) what the normal range of values they should be at?

I realize this question covers a lot of ground, but I don' really need an in depth explanation (although I would certainly welcome it if someone wants to provide it). A simple high-level abstract overview of each item would be more than sufficient.

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This is extremely wide question, so don't expect a single complete answer...

Anyway, I'll start by explaining some basic info.

First you have the signal acquired part. It simply states the frequency of signals going in both directions. After that you have the signal to noise ratio which you already know the meaning of. After that there's the received signal strength and power level fiends measured in dBmV. Decibell is a logarithmic scale unit and the formula to calculate it is . The mV part indicates with respect to what the ratio is calculated and in this case it's 1 mV RMS going through a 75 Ω cable and is used to show power level of television signal. Wikipedia says that normal measurement should be 0 dBmV.

After that you have the bit error rate field. It shows the number of bit errors divided by total number of transferred bits. So basically it shows how reliable the connection is. The lower number are better.

After that you have the modulation field. It simply shows how the signal is transferred. The interesting point here is QAM. It means quadrature amplitude modulation and is used to transmit more signals using a single signal as a carrier. Basically the signals are out of phase with each-other and each signal can then carry separate data. It's a very complicated field, so I'll just leave this articles: http://en.wikipedia.org/wiki/QAM, http://en.wikipedia.org/wiki/Phase-shift_keying, http://en.wikipedia.org/wiki/Amplitude-shift_keying.

I don't know what BP could mean.

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An absolutely excellent amount of detail. Certainly much more than I expected. I wish I could upvote your answer more than once. – kce Sep 12 '11 at 14:54
BPI is 'Baseline Privacy Interface', a method of encrypting the data stream between the CMTS and individual cable modems to help better protect against eavesdropping from a promiscuous listening device (I know of none) on same HFC node. – Nevin Williams May 24 '13 at 18:51