  Underwater acoustic sensor networks (UASNs) are often used for environmental
and industrial sensing in undersea/ocean space, therefore, these networks are
also named underwater wireless sensor networks (UWSNs). Underwater sensor
networks are different from other sensor networks due to the acoustic channel
used in their physical layer, thus we should discuss about the specific
features of these underwater networks such as acoustic channel modeling and
protocol design for different layers of open system interconnection (OSI)
model. Each node of these networks as a sensor needs to exchange data with
other nodes; however, complexity of the acoustic channel makes some challenges
in practice, especially when we are designing the network protocols. Therefore
based on the mentioned cases, we are going to review general issues of the
design of a UASN in this paper. In this regard, we firstly describe the network
architecture for a typical 3D UASN, then we review the characteristics of the
acoustic channel and the corresponding challenges of it and finally, we discuss
about the different layers e.g. MAC protocols, routing protocols, and signal
processing for the application layer of UASNs.
