'A box with a _command key was received.
Dispatch it to a local handler call it.
@param proto: an AMP instance.
@param box: an AmpBox to be dispatched.'

def dispatchCommand(self, box):

    cmd = box[COMMAND]
    responder = self.locator.locateResponder(cmd)
    if (responder is None):
        description = ('Unhandled    Command:    %r' % (cmd,))
        return fail(RemoteAmpError(UNHANDLED_ERROR_CODE, description, False, local=Failure(UnhandledCommand())))
    return maybeDeferred(responder, box)
