im devlping TFTP server with MINA, i have a prob…( describing here)

i want to send a packet and i need to for ACK,
if and only if ACK comes then i have to send next packet and so….
( here I must wait for ACK)

I tried( even now trying) but not geting… Hope u can do it easily,
If you can plz try and send me…..

thanq…….