docs: def _update_rto(self, R):
          """
          Update RTO given a new roundtrip measurement R.
          """
          if self._srtt is None:
              self._rttvar = R / 2
              self._srtt = R
          else:
              self._rttvar = (1 - SCTP_RTO_BETA) * self._rttvar + SCTP_RTO_BETA * abs(self._srtt - R)
              self._srtt = (1 - SCTP_RTO_ALPHA) * self._srtt + SCTP_RTO_ALPHA * R
          self._rto = max(SCTP_RTO_MIN, min(self._srtt + 4 * self._rttvar, SCTP_RTO_MAX))