Could use some troubleshooting recommendations

[notarat]

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 error is related to the inside wiring or my equipment so Comcast doesn't just blame me/my equipment.

 

[klank]

T3 and T4 errors means there is an issue on the cable network. Call Comcast to swap out the modem and watch it for a few days. If the problem still exists then call Comcast to roll a truck.

Do you have any splitters, amplifiers or other connections between the drop from Comcast and the modem?

 

[notarat]

T3 and T4 errors means there is an issue on the cable network. Call Comcast to swap out the modem and watch it for a few days. If the problem still exists then call Comcast to roll a truck.

Do you have any splitters, amplifiers or other connections between the drop from Comcast and the modem?

Comcast ran 1 line into my apartment when I got service installed back in 1997. They used a splitter about 6 inches out of the wall jack with 1 line going to the cable box and the other going to the cable modem.

I just purchased all-new wiring as well as 2 of the splitters on Comcast's "Recommended" list from Amazon and they should be arriving today.

I plan to replace all the wiring, the splitter, and my Ethernet cable just so I can say it isn't the inside wiring at fault.

I was thinking of putting a 4 port switch between the modem and asus router and connect the router to one port and my Raspberry Pi to another (bypassing the Asus router, in essence) Then, when the computer plugged into the router drops connection again, I can hop over onto the RPi to see if it's lost connectivity as well.

If the RPi has connectivity, then it would seem the problem lies in my computer's NIC rather than the router. (I say it would point towards my NIC because the previous TPLink router showed the same symptoms, and my onboard NIC card is the only shared component in the equation)

 

[klank]

Lets back up.

A switch between your modem and router will not work. Most ISPs only hand out DHCP to one single mac address connected to the modem. You have to power cycle the modem usually for it to learn a new mac address of a new device.

You need to eliminate your router and/or being the source of the problem. Do this by either hooking your computer or laptop straight up to the modem and see if the drops still occur.

T3/T4 drops are usually associated with losing signal/sync. When this happens your online light on the modem will either blink or go off. If this is the case then try the modem before any splitters. If it still happens time to call Comcast.