The speed of a propagating pulse in polymer networks is strongly influenced by their microscopic structure. The measurement of pulse velocity can be used to determine network parameters, including the molecular weight of the network between chemical cross-links (M-c) and physical entanglements (M-e). We report an experimental method for determining these network parameters from measurements of transverse velocity in stretched samples of well-defined polymer networks. We measured the transverse propagation speed in end-linked poly(dimethylsiloxane) networks under uniaxial tension as a function of the extension ratio, the degree of cross-linking, and the amount of swelling. To determine M-c and M-e from these measurements, we used the theory of elastic wave propagation and molecular models for the networks to relate network parameters to the wave velocity in deformed networks. We compare and contrast the values of network parameters obtained using this method with independent measurements of network characteristics from other measurement techniques.