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I have Comcast cable internet and I am connected using a DOCSIS 2.0 SB5101U Motorola Surfboard cable modem that I own. The surfboard is connected via ethernet to a Linksys E1200 router, and from there I am connecting a number of devices to the Wifi. It works pretty well, except that my connection drops at least once an hour. By that I mean that all devices in the room will simultaneously lose the wireless connection and then automatically reconnect in about 30 seconds. This includes multiple laptops, an iPad, an Android phone, etc. So, it isn't device specific. Sometimes the connection won't totally drop, but none of the web pages will load for a minute or two before it comes back. It affects every device at the same time though.

I've tried tweaking the settings on the router, such as setting the channel to be fixed instead of automatic. Also, I have connected my computer to the router directly using an ethernet cable, and I get the same behavior. When the iPad loses the connection, my ethernet wired laptop also loses internet connection (as in it gets the little yellow exclamation mark in Windows with "limited connectivity" written). It comes back just as fast, so it doesn't seem to be related to the wireless directly. It could be the router, but it is relatively new, and it worked much better (though not 100%) at my last apartment, so I doubt that it is.

Anyway, I called Comcast to complain and get someone out here to fix it, and I have had multiple reps tell me that my modem is "past it's service life" and no longer supported. They say that the network is now upgraded to be DOCSIS 3.0 and that I must upgrade my modem before they will help me further. Everything I've read seems to suggest that DOCSIS 3.0 should be backwards compatible, and that this modem will only limit my speed. Since I'm only paying for the low tier 20Mbps, I don't care that much about that. They want me to buy the Motorola SB6141 Surfboard modem to replace mine. It's $80, so I wasn't quite in a hurry to do that. Do you think that will fix it? Or is there something else I can try?

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To me, this sounds far more likely to be a wireless problem than a DOCSIS problem.

When the wireless drops happen, does wired Ethernet access to the Internet still work the whole time? To test, leave a machine plugged in via Ethernet to a LAN port on the E1200, make sure you've turned off wireless on that machine, and leave it doing once-per-second pings of an IP address of a reliable box somewhere at your ISP or elsewhere on the Internet. Then, after the next wireless drop happens, see if the wired pings were interrupted.

If the wired connection is getting interrupted at the same time, it might be that your E1200 is flaking out and/or spontaneously rebooting, or it might be that your cable modem is doing the same, or it might be that your cable line is having problems. Do you have TV service on the same cable line? Does your TV service drop at the same time? (I'm talking about normal TV channels, not IP-based streams like on-demand, Netflix, Hulu, etc.)

If the wired connection isn't getting interrupted, then the problem isn't your cable modem, it's probably your Wi-Fi AP or the wireless medium itself (i.e. severe acute transient 2.4GHz radio interference).

Do you have the latest firmware on your AP? Make sure you do, because maybe there was a bug that made E1200's flake out or crash and reboot that Linksys already fixed.

Do the drops correspond to when someone uses the microwave oven or the cordless phone? Do you live in a dormitory, apartment, condo, townhouse, duplex, or semi-attached house or other kind of relatively high-density housing situation? What channel is the AP on now? Does the problem happen when the AP is on other channels? Be sure to test channels 1, 6, and 11.

I guess the gist of my Answer is that there are a lot of different things that may have gone wrong, and it seems like you jumped to the conclusion that it's your cable modem without actually doing any kind of normal process-of-elimination troubleshooting. Your current problem description leaves too many variables in play. You need to do a little more of your own legwork isolating the cause of your problem before anyone else is going to be able to help you.

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I totally get what you're saying and I completely agree, there's too many variables. I also tested with a wired connection to the E1200, and I found that the connection drops at the same time as the wireless for other devices when it happens. I don't have TV service so I can't test that. I've tried channels 6 and 11, and I already flashed the latest firmware. I get the same behavior. It's on channel 6 now. I only jumped to the cable modem conclusion because Comcast insisted on it. I'll be doing more experimentation, I'm going to borrow a router from a friend to see if that works better. – mattgmg1990 Nov 21 '13 at 7:29

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