docs: def _send_request(self, xml_request):
          """ Send the prepared XML request block to the CPS using the corect protocol.
  
              Args:
                  xml_request -- A fully formed xml request string for the CPS.
  
              Returns:
                  The raw xml response string.
  
              Raises:
                  ConnectionError -- Can't establish a connection with the server.
          """
          if self._scheme == 'http':
              return self._send_http_request(xml_request)
          else:
              return self._send_socket_request(xml_request)