Some players have reported constant connectivity issues with the game. Not only, that but at some points the game also freezes up. These complains seem to be generating more for the PS3 version, even though PC and Xbox 360 players have reported similar issues.
Activision posted on twitter that they are aware of the problems and are looking at it right now.
We are aware of connectivity issues that some players are facing in Black Ops II on PlayStation 3. We are working on resolution, thank you.
For now, the company has advised PC gamers to use only the latest drivers for Black Ops 2.