: Diameter CM state machine

Hi
	I have some doubts about the DIAMETER state machine (sec 5.6 of
RFC 3588):

1. R-Open    R-Rcv-CER        R-Snd-CEA        R-Open
    
I-Open   I-Rcv-CER        I-Snd-CEA        I-Open

What is the use of the state transition considerations above? 
Could any one tell me how after the peers have exchanged CER-CEA (& thus
moving to the open state) can receive a CER again?

2. For the above 2 transitions, if the received CER has some protocol
error, what should be the behaviour? Ignore / only send error CEA / send
error CEA  & close connection?

Regards

Rajith