Need some troubleshooting tips for dropped internet

So...I have a pretty basic network layout in my apartment (See pic)



Cable Modem and Router are on the same UPS and are the only devices plugged into it. I did not run the cable for the cable modem through the coax port on the UPS though.

I'm having some major problems which are causing me major headaches.

Problem:
Every single day my connection will drop for anywhere from 5 seconds to 30 seconds then re-connect. It repeats this several times in a row, and it occurs several times a day. I've done the ol' "power cycle the modem and router" bit and it never improves. Sometimes it goes away for hours, most times, though, it continues within a couple minutes after powering everything back up.

What I'm looking for are recommendations/advice on how to check to see where the problem actually is...


Background info (if you want to read it)

Troubleshooting Efforts Thus Far:

1 -- I replaced the previous router (a TP Link 10/100) with the Asus because of this issue. No Change. This tells me it isn't the Router that is at fault.

2 -- Thinking it could be the modem, I purchased a new Cable Modem (Motorola 6120) and have it ready to swap into the old one's place. Since swapping the modem out requires a call to Comcast I have not yet done this...but it is something I can do today

3 -- I checked my Signal Levels on the Cable Modem by accessing the modem's management interface, and the values look to be within the acceptable ranges, but they are close to the high end of the range of acceptable levels.

Cable Modem Signal Levels:
Signal to Noise Ratio is ~37dB
Downstream/Upstream is 41dB/9dB (I may have swapped the two numbers...)
(the 9dB entry is close to the 10dB limit, according to Comcast)

I've tried looking through the cable modem's logs and I'm seeing some T3 errors and T4 errors. Unfortunately, the entries are not recorded in an easy to understand syntax so I'm not sure what to make of the entries...and it's compounded by the fact that power cycling the cable modem causes the date to revert to 1970(!!!)

Are there any sort of tester devices I can connect inline to record the connection drops/signal levels?

What I hope to do with my troubleshooting is eliminate the possibility that the dropped connections are related to the inside wiring or my equipment so Comcast doesn't just blame me/my equipment.

Since you already have the new modem go ahead and swap it.

Are all devices losing internet at the same time or is it limited to wired or wireless?

ATMINSIDE said:

Since you already have the new modem go ahead and swap it.

Are all devices losing internet at the same time or is it limited to wired or wireless?

Click to expand...

Usually by the time I notice the problem and run over to get my HTC One in order to see if the wireless is working, it has stopped. I will call Comcast this evening when I get home and go through the process of swapping out the cable modem.

I was thinking of putting a 4 port switch in between the cable modem and my Asus router, then run a cable from the switch to my Raspberry Pi, and another cable from the switch to my Asus router. I could use the Raspberry Pi when I notice a connection drop to see if the connection that doesn't go through the Asus router is working...but...although it would seemingly narrow down the cause to some sort of problem between the cable modem and Asus router, it doesn't explain why the TP Link router I replaced with the Asus displayed the exact same symptoms.

Put the 5 port switch between the modem and router and run a continuous ping on a device on the switch and one on the router.

The downstream power level is more between -12 to 12 so you are fine at 9. All your other levels look good as well, I take it the modem only gives one SNR? Install the new modem anyhow, should be pretty painless, just give them the new mac and they should get the new modem up in no time, I have seen modems overheat and have similar symptoms. Log into the modem and just refresh when it is down to see if it has lost it's signal. Also do you have the modem in bridge mode or doing double nat?