Successful prediction of the performance of medium access control protocols is dependent on a realistic model of the underlying propagation channel. Such a model needs to capture the characteristics that are pertinent to the operation of the higher layer. The majority of MAC protocols proposed for underwater acoustic communication networks have so far been evaluated based upon propagation models which often capture only the most basic characteristics. This PhD will explore whether other characteristics of acoustic wave propagation need to be captured at the MAC layer, through detailed studies of state of the art channel models used in physical layer research. New propagation models will be developed to provide a MAC layer simulator with a more realistic model of time-varying link availability and packet reception, for comparison with existing models.