Some ISPs operate time outs. My last ISP operated 2 types:

1: A maximum connection time of 3 hours.

2: A cut off after so many minutes of inactivity this could mean that if I was simply reading a long thread here, I could get cut off because there was no data being sent to and from my ISP. If suspect that this might be your problem, try tuning into one of the Mudcat Radio Archives anything else that should ensure there is always some data flowing. It is possible to keep pinging your ISP at periodic intervals but I know that my last ISP did not allow that so it is probably best to choose something that at least makes it look as if there is some legitimate activity going on.

Jon