Small internet problem

Hey,

Recently when i leave my computer on overnight to download like large files, about 2-3 days later the speed when using the internet the speed drops dramatically, and i either have to refresh the page a couple of times to get everything to show properly, or sometimes the page doesn't even load at all. It does return to normal usually within like another 2-3 days, but i was wondering if you guys might know what might be causing this? I do have a monthly cap of 30GB (the ISP doesn't specify what the daily cap is, i assume it's 1GB a day), so i'm guessing if i go over it, they restrict it or something like that.

How do u access the net?
directly or by router and which type?

the problem might something like this:
IP-connections which are not properly disconnected usually stay there for whole 5 days. My ISP disconnects me every 24 Hours, so alot of connections are not closed properly. The number of open connections builds up until the router can't handle that much anymore. (about 3000 in my case; i just don't know why it can't handle that much. afaik max connections are only limited by RAM. my router has 64mb which should be enough for several thousands)

The easiest way to get around this is to reboot your router / directly connected PC everytime it gets too much.

The solution is to set the timeout for open connections to a smaller value. (I've set it to 1 day since i get disconnected every 24h)
Problem: With most "Hardware"-routers you won't be able to do that. So the only way would be to reboot it every 2 days or so...

hope this helps...