I don't know. I have called the isp numerous times about the issue, and they always say everything seems fine on their end that they can tell. They have sent a guy out to check things out twice, and both times couldn't find a problem.
I think it is possible that the problem could be wiring. It doesn't make any sense at all though. The router gets shut on and off randomly as if it is losing, but only when connected to the modem. The ups filters the electricity going to the modem and the router, and even filters the coaxial cable connection itself. I have gone through like 4 routers that all have this problem, and two different cable modems. Nothing seems to work.