Underwater Acoustic Sensor Network (UASN) has become increasingly important, with numerous applications emerging from various areas such as commercial, environmental-research and defense. This paper provides a comprehensive view of current state-of-the-art in UASN by analyzing the research done by various communities. It briefly states the basics of underwater acousticcommunication and cites advances in research and development at various layers of networking modules, namely physical, data link, network, transport and application layer.

It also covers interesting new concepts of cross-layer protocol stack design along with requirement of network management protocols pertaining to UASN. Finally, various hardware, software tools and test-beds developed by prominent universities/research organizations are described. We also briefly provide information about the test-bed set-up at our laboratory at BITS -Pilani K K Birla Goa Campus.