Internet repeatedly lost but wireless network stable

I have Cox cable running through a Scientific Atlanta DPC2001R2 cable modem into a D-Link WBR-2310 wireless router to two laptops.

At unpredictable intervals, from once or twice a day to several times in one hour, the internet will go out on either or both computers. The network connection however does not go out. Disabling and re-enabling network connection on the computer restores the internet connection for that computer.

What could be causing this and how do I fix it. I assume there is some setting I could change in how the router and the modem interact.

Thanks for any help! this is very frustrating!