If it is a dynamic IP and if the lease is expiring you can avoid the annoyance by "re-leasing" (option in your router menu somewhere) the IP address and getting a new one before you start anything time consuming. The lease should last for 4,8,12,24 hours depending on your ISP. Look for something ike DHCP release adn DHCP Renew.
If the IP is static (your ip address never changes) then it's not a lease issue.
It could be a problem with an inadequate signal level on the cable line. Cable companies are notorious for not maintaining quality connections (or as in the case of a friend of mine his neighbors are stealing cable so they screw it up every now and then splicing into the line). Or the modem sensitivity could be degrading with age.
Check the lease first if that is not the problem call the cable comapny and ask. You may need to do a lot of *****ing to get them to check it but hey, you're paying $600 a year for life so it better be up to spec! If the cable company blows you off try calling your city councilman. They hate the cable comapnies too.