code: def _send_loop(self):
          
          while self._enable_send:
              hub.sleep(self._xmit_period)
  
              # Send BFD packet. (RFC5880 Section 6.8.7.)
  
              if self._remote_discr == 0 and not self._active_role:
                  continue
  
              if self._remote_min_rx_interval == 0:
                  continue
  
              if self._remote_demand_mode and \
                      self._session_state == bfd.BFD_STATE_UP and \
                      self._remote_session_state == bfd.BFD_STATE_UP and \
                      not self._is_polling:
                  continue
  
              self._send()
docs: A loop to proceed periodic BFD packet transmission.