What is offline mode in minecraft?

I play minecraft for the playstation 3 and while I'm playing online with my fiend as a host it constantly exits and reloads the game and says switching to offline mode and kicks my friend, I have to exit the game and reload it for him to join again. How do I keep it from switching to this "offline mode"?

Normally that occurs when the Wi-Fi signal is not as good as it should be to work with the data that "online mode" is using. If your signal is weak, or not fast enough to handle the game, it defaults to offline mode.

Hope this helps!