Question Trouble pinpointing possible issue with my internet


Aug 31, 2013
Hello, looking for some assistance in figuring out what could be causing some internet issues as i'm not a big networking guy.

Roughly a week ago, I noticed a severe drop in download speeds (from roughly 800mbps to 30mbps) as well as extremely varied packet latency (jumping between 20ms to 170ms all over the place) and started doing some troubleshooting. I did the usual of checking the PC connections, power cycling the modem, re-seating the connectors on the modem, and changing IPs/using a VPN to check for throttling. Of all the steps, power cycling seemed to recover some download speed but would quickly dip back to around 30mbps after 10-20 minutes. I called my ISP(Cox) to try and see if it was on their end potentially, and was told that my modem was throwing errors and that they'd send a new one.

While i've been waiting on that new modem, I did a bit of digging into both the modem's control panel, as well as the coax lines, at the behest of a friend that knows a little bit about networking. I discovered two potential problems; the modem is showing a lot of Uncorrectable Codewords in its CM Error Codeword table as well as showing some very confusing data under its Downstream Channel Value table. The second potential problem is that the coax line runs outside to a splitter (more than likely to provide a coax out port to the upper floors of our house) and it's exposed to a lot of sea air and looks fairly crusted. Below are the tables for those that can better help me interpret this.

DownstreamChannel Bonding Value
Index 2112345678910111213141516171819202223242526272829303132160159160
Lock Status LockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedNot lockedLockedLockedLockedNot lockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLockedLocked
Frequency 237 MHz117 MHz123 MHz129 MHz135 MHz141 MHz147 MHz153 MHz159 MHz165 MHz171 MHz177 MHz183 MHz189 MHz195 MHz201 MHz207 MHz213 MHz219 MHz225 MHz231 MHz243 MHz249 MHz255 MHz735 MHz741 MHz747 MHz753 MHz759 MHz765 MHz771 MHz777 MHz918 MHz300000000918000000
SNR 38.8 dB0.0 dB30.7 dB33.3 dB33.8 dB34.0 dB32.6 dB32.7 dB35.5 dB35.2 dB35.8 dB0.0 dB0.0 dB0.0 dB33.4 dB0.0 dB35.5 dB36.9 dB37.7 dB37.9 dB38.5 dB38.7 dB38.9 dB39.2 dB41.3 dB41.6 dB42.1 dB41.5 dB41.9 dB40.8 dB42.2 dB42.3 dB41.8 dB40.5 dB41.8 dB
Power Level -14.0 dBmV-18.4 dBmV-17.9 dBmV-17.5 dBmV-17.1 dBmV-17.1 dBmV-17.5 dBmV-17.7 dBmV-16.8 dBmV-16.4 dBmV-16.6 dBmV-16.6 dBmV-17.2 dBmV-16.8 dBmV-15.8 dBmV-15.3 dBmV-15.5 dBmV-14.9 dBmV-14.8 dBmV-14.7 dBmV-14.3 dBmV-14.1 dBmV-14.0 dBmV-13.3 dBmV-6.7 dBmV-6.8 dBmV-6.5 dBmV-6.4 dBmV-6.1 dBmV-6.4 dBmV-6.5 dBmV-6.1 dBmV-4.2 dBmV-11.4 dBmV-4.2 dBmV
Modulation 256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAMUnknown256 QAM256 QAM256 QAMUnknown256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAM256 QAMOFDMOFDMOFDM

UpstreamChannel Bonding Value
Index 12345
Lock Status LockedLockedLockedLockedLocked
Frequency 17 MHz23 MHz30 MHz36 MHz36 MHz
Symbol Rate 51205120512051200
Power Level 54.5 dBmV54.5 dBmV54.5 dBmV54.0 dBmV48.0 dBmV

CM Error Codewords
Index 12345678910111213141516171819202122232425262728293031323334
Unerrored Codewords 1972479251243143756030631651973373375786337415054133005877453326035817311424900030200658043199949306317153360603166815406304559040832110275570336632527733794829523379417352326827184330615242353382717320338275171633830968453383146262338315081633831533703383160725338316522733831663493383168212338317208821019739901972479251
Correctable Codewords 1451921227602293515251834055281390830503642042664327238131232213134231216207791523833067044156152549890803697983215772992962415931827561249291334353080730028227724223121821528420296606041451921227
Uncorrectable Codewords 907624363163354874447350831535223703038371346132637635173035532351896330709050162768614409261324243010772841007733927575734210497447287997250828135961000000272189899076

I've been power cycling the modem every 24 hours and checking these charts every 24 hour period and its been consistently like this for at least 3 days.

My question is what is the most probable cause? A bad modem, corroded cabling, or a fault directly with the ISP? And, what steps should I take to resolve these issues?

Thank you for taking the time to look at this, i'd appreciate any help in getting some answers.
Signal levels are not in the recommended range. Upstream is likely the largest issue but the downstream channels are not the best and they have inconsistent values which sometime causes more issues.

This is generally some kind of cabling issue. Can be as simple as a small bit of water in some connection. It is likely outside your house but you can check the wires inside before you call the ISP