Underwater wireless communications can enable
many scientific, environmental, commercial,
safety, and military applications. Wireless signal
transmission is also crucial to remotely control
instruments in ocean observatories and to enable
coordination of swarms of autonomous underwater
vehicles and robots, which will play the role
of mobile nodes in future ocean observation networks
by virtue of their flexibility and reconfigurability.
To make underwater applications
viable, efficient communication protocols among
underwater devices, which are based on acoustic
wireless technology for distances over one hundred
meters, must be enabled because of the
high attenuation and scattering that affect radio
and optical waves, respectively. The unique characteristics
of an underwater acoustic channel —
such as very limited and distance-dependent
bandwidth, high propagation delays, and timevarying
multipath and fading — require new,
efficient and reliable communication protocols
to network multiple devices, either static or
mobile, potentially over multiple hops. In this
article, we provide an overview of recent medium
access control, routing, transport, and crosslayer
networking protocols.