Sorry to hear about the connectivity issues with both Modern Warfare 3 and Black Ops. Are you still experiencing the same issue? If so, what console do you have the game for? Also how long have you been having this problem for?
One thing we suggest is to reboot the router and modem. If it's still causing issues try the following as well:
For Xbox 360 - Clear the system cache.
For PlayStation 3 - Remove the game data file and redownload the DLC and updates.
I would also like to find out what your Internet Service Provider is as well. So keep us posted if the problem still continues. Thanks!^RT