code: def start_pinging(self) -> None:
          
          assert self.ping_interval is not None
          if self.ping_interval > 0:
              self.last_ping = self.last_pong = IOLoop.current().time()
              self.ping_callback = PeriodicCallback(
                  self.periodic_ping, self.ping_interval * 1000
              )
              self.ping_callback.start()
docs: Start sending periodic pings to keep the connection alive