Fast retransmit for flooding-based routing in underwater wireless sensor networks

In underwater wireless sensor networks (UWSNs), flooding-based routing protocols are preferred for reducing routing overhead. In addition to routing, a transport protocol should operate to provide the end-to-end reliability in USWNs. Fortunately, the Fast Retransmit technique can be exploited for fast retransmissions of lost DATA segments. However, if it operates over the flooding-based routing protocols, each source node will receive multiple copies of ACKs which are transmitted along different paths. Since the source node cannot distinguish between these multiple copies of ACK segments and real duplicate ACK segments (defined as an ACK indiscretion problem in this paper), unnecessary retransmissions are performed. In this paper, we therefore propose a new Fast Retransmit technique to address the ACK indiscretion problem. In our proposed technique, the sink records a new count number into a header, informing how many duplicate ACK segments have been transmitted from the sink. The source nodes becomes aware of the number of duplicate ACK segments transmitted from the sink and can perform the Fast Retransmit correctly.