Handling lost connection with smack

hii all,

Now, i develop an android messenger, and i use smack for API to connect with openfire.

But, I have some question :

1. some time client A send message to client B and Client B receive the message, and some time Client B can't receive a message from Client A, what i must to do to fix this condition?
2. in stand by condition, some time i having a lost connection to internet, and then reconnect again, but my roster showing offline for all user. how to make handling to reconnect to server / restore session if some time i having lost connection?

I hope any one can help me to solve this problem .

Thank you