blocking of recvfrom() even if data has been sent
 

hi,
i am trying to transfer a file using UDP. When I am sending the file byte by byte , it reaches the receiver. But when I am sending more than one bytes at a time in a packet, the receiver blocks after some time . It is not able to receive the whole file. What can be the reason ?
The sender is sending all the packets but receiver is getting blocked at recvfrom() somewhere in between.