  We consider time domain acoustic scattering from a penetrable medium with a
variable sound speed. This problem can be reduced to solving a time domain
volume Lippmann-Schwinger integral equation. Using convolution quadrature in
time and trigonometric collocation in space we can compute an approximate
solution. We prove that the time domain Lippmann-Schwinger equation has a
unique solution and prove conditional convergence and error estimates for the
fully discrete solution for smooth sound speeds. Preliminary numerical results
show that the method behaves well even for discontinuous sound speeds.
