Start sending periodic pings to keep the connection alive

def start_pinging(self) -> None:
        """Start sending periodic pings to keep the connection alive"""
        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()