I’ve got some problems with internet connection lately: sometimes it works just fine – sometimes it just disappears. It happens several time during a day and it’s rather on ISP/cable modem problem. Before I’ll start to discuss with ISP I would like to have some numbers in my hand - so basically I’m looking for a freeware program that monitors if I’m on-line and logs it to simple text file. Any suggestions?

I see a shareware that will do exactly that : http://www.connectionmonitor.net/ It's not freeware, but you can use it without registration for 30 days

Could you define on-line? Are you talking about an established IP connection, or a connection to your provider (e.g. DSL connection)? There's a crucial difference (ISP wise), so you might want to have a more detailed look into what's going on behind the scenes before contacting the technical support. At least I found it useful to have such data present for the (rare) case that you find somebody on the line that actually knows what s/he's talking about and that can really help you. I'm going to assume (though that's a sin with computers and especially programming ;)) that you have a router of some sort, so if you tell us which one you obtain, it's likely that your router actually records these data by default (or has an option to record it for you), which would be better than any program, given that the router has access to a far more detailed protocol.

I use Motorola SURFboard cable modem SB5101E received from ISP and connected to my PC via network card. It’s equipped with 4 green lights that (if all goes fine) after short blinking give a steady light. Those lights are marked as power, receive, send, online. So normally it looks like this: I turn power on: green “power light” lights on, than “receive light” starts blinking and after few seconds it give steady light, after that “send light” starts blinking and after few seconds it give steady light …and so on. Now after “online light” lights steady - “PC activity” light starts blinking and I’ve got access to internet.
My problem is that without powering modem down it looses connection to network. Those green lights starts to blink like modem was just turned on and it sometimes take 10 min to reestablish connection – sometimes it takes 2 hours. I checked cables – no problem here. While this blinking I still have IP address assigned, I can ping gateway (which probably is the modem) but I can’t access any internet site (or ping google – what I can do while on-line). ISP wants to replace my modem – it’s an obvious solution but I’m not sure it will help. Modem is an electronic device - it either works or not. It could work for some time – and than stops working but it’s loosing connection at random and than it reestablishes it. Doesn’t look as hardware problem to me. The worst case is that they want to send a tech guy to my place to check modem. But what if guy comes here and modem will behave properly (as I said failures are at random order)?

Thanks for your post. I've got now full access to diagnostics of my modem. With it I was also able to google some message boards with people having similar problems. Cannot really say when I loose my connection most frequently. I’ve started monitoring it just today. What I noticed that I’ve got my modem set to: Upstream Channel ID 4. When all is fine on Signal Page Upstream Channel Id is also shown as 4 with a steady Power at 48 dBmV. But when I go off-line Channel Id changes from 1 to 4 every time I refresh page and Power is ranging from 10 to 59 dBmV.
So it seems that it's truly cable lines & signal quality problem. Which is bad news for me - I don’t expect ISP will take extra effort to find a random problem and solve it.

I've had this exact same problem with a Motorola cable modem, although mine was hooked up to an Asus router/switch/wi-fi access point. I had gotten a new NetGear cable modem/router/switch/wireless access point with a new internet subscription (the Motorola was from my previous one, although from the same company), but kept the old setup because I had everything configured the way I wanted it. Then the exact same thing you're describing started to happen. Several times a day, for anywhere from 5 minutes up to two hours. In the end, I believe I fixed it by switching over to the NetGear equipment. So it may very well be your cable modem that has developed a periodical error like mine did, and those are the worst to debug.

If they are willing to replace the equipment without sending a technician, that's certainly worth a shot.

Actually, there are multiple possible issues, ranging from something as trivial to heat (both on the line as well as on the router itself), to a buggy port on the ISP.
I wouldn't give up hope yet if I were you, there are plenty of cases that your ISP *can* handle and some of them even do :p

Just give them a call and describe the problem, I'm sure they're going to give it a try.

Ok, thanks for all help. I think with this info I got now - it will be easier to speak to ISP. I mark HampsterStyle's post as a solution...and +1 Rep for Phc7006 - thanks again.