The paper describes the Dual Channel Acoustic Communication Protocol (DCAP) and the results of its experimental trials. This open protocol has been developed as an extension of the SWiGacoustic standard proposed by the SWiG Working Group considering requirements and use cases. It enables networking capabilities, simultaneous low and high rate data transfer among acoustic nodes, and frequency division multiple access to the underwater channel. First, the protocol specification and the details of its implementation are described. Then, the methodology for the feasibility testing is presented, followed by the experimental trials at sea in two different environments: confined and open water. The results achieved show the feasibility of using this protocol to allow a network composed of acoustic nodes to simultaneously use low and high rate channels to exchange heterogeneous data through TDMA and FDMA.

The classical result of Lloyd for the optimum scalar quantizer in the asymptotic case of fine quantization is derived from first principles. The derivation is offered as a simple alternative to Lloyd's original and elegant piece of analysis, and the result is used to derive the optimum compander. We then show why a compander that presents uniformly distributed random variables to the quantizer is not a good idea.