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I have a Motorola SB5120 cable modem. My provider is Atlantic Broadband in North Miami Beach. I've had this modem for over 5 years and has always worked the same way. Even in 2 different locations. The connection is fast and all of a sudden it pauses. For example, I'm watching a YouTube video and you can see the loaded part of the video loading very quick until all of a sudden it stops. Changing the video quality (higher or lower) makes the movie continue loading. Another example is file downloads. It doesn't matter how big or small the file might be. I'm downloading and boom, out of nowhere, it stops. Sometimes I have to restart the download 5/6 times before it finishes. Now with all the video content being delivered through the web (Roku, Netflix, HBO Go, Xbox, etc) it is getting very frustrating for the buffering to appear.

I have download speeds of 12 mbps and various speed test throughout the day confirms it. I also download files at over 1MB per second, so it doesn't sound like speed is the issue.

My question to you is. Can it be the modem? Is it possible that modem doesn't handle those high speeds? Maybe it's defected? Maybe I can modify some of the settings in the modem. Or should I just get a new modem?


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The modem was not provided by the cable company. I bought it at Best Buy, but it is the same model that they used back then. – Jonas Stawski Apr 30 '12 at 14:52
up vote 1 down vote accepted

Could it be the Modem? Since you imply that you have connected different devices on your network and experienced this same issue, it certainly isn't any one computer. So, yes. It could be the modem.

Since you have multiple devices (you mention XBox, and you are typing on a computer, so that's two) you must have a router. Have you used the same router for all that time as well? If so, the problem could be your router.

Have you contacted your cable company to have them check your modem from their end? If you did not purchase this modem on your own, I would contact Atlantic Broadband and request a new modem. After 5 years, you deserve one.

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The specs say max download rate is 38 Mbps, so 12 should not be difficult for it to handle. The important question is, when everything slows down, are you using the full 12 Mbps that your connection allows? You may very well be over-utilizing your connection.

There are multiple things that can cause a slowdown when it comes to cable (or DSL). Cable runs on a shared pipe as any other, so it is possible that the trunk is over-utilized. It is also possible that your own connection is simply over-utilized. It could also be a bad modem. It could be a problem between your router and your modem or your modem and the wall (cabling), or even your router.

Swap out all the cables you can, also connect directly to the modem and bypass your router. Do things improve?

Do you have another modem to test with? if so, swap it out, does it stay the same?

Are you using the modem from another service? if so have you gotten the specs for this service to ensure you are using all the correct parameters?

If you connect the modem to different places in the house (say where the cable comes out on the other end, either at the side of you house, or in the garage) to see if it works better there?

These are all things that your ISP will likely have you test before taking action on their end, so it is a good idea to get it out of the way and take good notes. If you get to that last step and it is still slow, that basically takes everything on your side out of the picture and leaves the issue on the cable companies plate to deal with - give them a call then.

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