With cable television, confining the application of the compulsory license provisions of the Copyright Act to the territory of the United States does not pose a major technical challenge: the wire must stop at the water's edge. Direct broadcast satellite poses a greater challenge, since the "footprint" on the ground where the satellite signal can be received often crosses national boundaries. However, since these signals are encrypted and require a special decoder for viewing, territorial limitations can be enforced by controlling the availability of the decoders.