  In this paper we propose and analyze a fully discrete method for a direct
boundary integral formulation of the scattering of a transient acoustic wave by
a sound-soft obstacle. The method uses Galerkin-BEM in the space variables and
three different choices of time-stepping strategies based on Convolution
Quadrature. The numerical analysis of the method is carried out directly in the
time domain, not reverting to Laplace transform techniques.
