  We compute the strong coupling limit of the boundary reflection factor for
excitations on open strings attached to various kinds of D5-branes that probe
AdS5 x S5. We study the crossing equation, which constrains the boundary
reflection factor, and propose that some solutions will give the boundary
reflection factors for all values of the coupling. Our proposal passes various
checks in the strong coupling limit by comparison with diverse explicit string
theory computations. In some of the cases we consider, the D5-branes correspond
to 1/2 BPS Wilson loops in the k-th rank antisymmetric representation of the
dual field theory. In the other cases they correspond in the dual field theory
to the addition of a fundamental hypermultiplet in a defect.
