dial up internet connection freeze

I have a celeron 400, 256 ram with win98 and a 56k dial up connection through my phone line. I will be on the internet and in the bottom right corner my conection will show that I am connected represented by the two green blinking monitor symbols near the clock. Then after I am on for a bit the green goes out, I am still connected but nothing happens. Then after maybe 10 seconds to sometimes 3 minutes the green light will reappear and then my internet activity starts again. Is this my isp, modem,?????