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I have Comcast HSI. I have a Motorola Surfboard SB5120 modem which I own. I have a business-related Juniper box that plugs into the modem. My Linksys E4200 router plugs into the Juniper and then the computers on the network plug into the Linksys.

For the past few days, I've found that my internet connectivity has been turning off for a few seconds and then reconnecting. In normal usage, I probably wouldn't even notice it, but I use a business program that runs from the cloud and it stops and notifies me each time it disconnects and reconnects.

I am trying to isolate the problem. I've called Comcast and they say there's no problem with my service. I've power cycled all above mentioned devices. I have now bypassed both the Juniper and the Linksys router and have my system connected directly to the modem and the problem continues. I have also noticed that the modem's status lights do not change when connectivity goes out.

Does this mean the modem is likely bad (it is by far the oldest component involved)? If so, what should I buy to replace it?

Thanks.

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it could be the modem, try a new piece of cable? , comcast doesn't check anything as far as line quality, if they can see your modem, they stop looking, not a criticism, if you get a new modem you might consider something that supports DOCSIS 3, comcast has rolled that out to most places, perhaps your area

It isn't the cable because different cables are used whether the router is plugged into the modem or if my computer is plugged directly into the modem.

After posting signal levels & trace results to DSLReports someone told me that:
"Your downstream SNR is quite low (32 dB). It is quite likely that it is fluctuating enough that your modem is losing sync.You should call tech support and have them come out to investigate the signal."

Does that sound possible, and it it something that Comcast would deal with? While I don't mind buying a new modem, I want to be sure it will solve the problem if I do so.

have you inspected all the coax connections? outside as well, you can certainly schedule a service call with comcast, they will check signal at the nearest box, like next to the sidewalk that feeds a couple addresses, then likely out side, then at your wall, they also sell this tester at Home Depot, but if they can come out in a reasonable time for you, but have a look at your coax cables for now .

CMeys said:   
Does that sound possible, and it it something that Comcast would deal with? While I don't mind buying a new modem, I want to be sure it will solve the problem if I do so.
It is more than possible. But the only way to be sure is to have them test it. They can only do that with a service call

More likely than a modem problem

I had a very similar problem with my Comcast internet a few months back. The only difference between my problem and your problem, from what I can tell, is that when my connection dropped it would be out anywhere from a few seconds to hours.

ellory is right - the only way to know is to have a technician come out and measure your signals.

For my issue, as soon as the technician arrived and I told him the symptoms, he immediately knew that the issue was a poor signal (too low SNR ratio, like you have). He verified this by measuring the signal at the box outside and ran a new cable for me.

Call Comcast and tell them you need to have someone come out and check the line between the box and your house.

Thanks. I've got Comcast coming out tomorrow.

Comcast was here today. After checking inside the tech went outside and looked at the connections. He replaced all of them reporting that they looked "nasty". All seems well now.

I am also inclined to replace my modem. I presently have a Motorola SB5120 which I own.

I was looking at the Motorola SB6141 -- I am on Blast -- will I benefit additionally from a DOCSIS 3 modem?

CMeys said:   Comcast was here today. After checking inside the tech went outside and looked at the connections. He replaced all of them reporting that they looked "nasty". All seems well now.

I am also inclined to replace my modem. I presently have a Motorola SB5120 which I own.

I was looking at the Motorola SB6141 -- I am on Blast -- will I benefit additionally from a DOCSIS 3 modem?



what kind of speeds do you get?


i'm @ 25 down 3 up, i downgraded from blast to "performance internet or some such BS" save some money and the speed didn't change

DOCSIS 3 binds multiple streams, but check your speeds now and report

speedtest.net

Speed is great -- around 34/6 now and was only a little less than that before the tech was here. My issue wasn't about speed it was about the connection going out numerous times daily for a few seconds. It seems fine now, but I think I will get a new modem (probably the SB6141) since mine is the SB5120 and is around 7 years old.

Why are you getting a new modem?

ellory said:   Why are you getting a new modem?

I don't know that it is really necessary, but I want to be sure that my old one isn't problematic and that way I'll be able to take advantage of the D3 available here.

You found the problem. Bad connectors / splitter /cable

If it was me, I would leave well enough alone



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