Recovery of an incomplete transfer of a file from a sender to at least one recipient connected to the sender via a network is disclosed. In an example embodiment, the at least one recipient receives one or more packets of the file sent by the sender via the network. The at least one recipient sets a bit in a bitmap, for each received packet, to efficiently keep track of and request for retransmission of missing packets. Thus, after the file is sent by the sender, the at least one recipient requests from the sender a retransmission of any packet corresponding to a bit that has not been set. The sender then sends packets including the missing packets via unicast to the at least one recipient which has sent a request for retransmission.