Underwater sensor networks are an important field of research. Several
applications require the use of this kind of networks like tsunami or oil spill
alerts. The underwater medium is very harsh and only acoustic signals can be
used for the transmission of information. The use of this kind of networks is
still in a developing state far from reaching standard consensus on basic
aspects like carrier frequency or modulation techniques. The use of these
networks for realtime applications has not been analyzed previously. In this
paper we present two solutions for the scheduling of real-time messages and we
provide a time constraint analysis of the performance of the network.