AT+CIPMODE=1 
OK 
AT+NETOPEN 
OK +NETOPEN: 0 
AT+CIPOEPN=0,"UDP","1.241.xxx.xxx",45000 
ERROR 
AT+CIPOEPN=0,"UDP","1.241.xxx.xxx",45000, 25000,-1 
ERROR
AT+CIPOEPN=0,"UDP","1.241.xxx.xxx",45000, 20000
CONNECT 115200 

Finally I can send AT+CIPOPEN command without error.
I misunderstood syntax of this AT+CIPOPEN command, I missed my local port (ex. 20000 in above command usage) FYI. +++ is the exit code in transparent mode

Thank you for the hint !