code: func (c *cubicSender) OnRetransmissionTimeout(packetsRetransmitted bool) {
  	c.largestSentAtLastCutback = 0
  	if !packetsRetransmitted {
  		return
  	}
  	c.hybridSlowStart.Restart()
  	c.cubic.Reset()
  	c.slowstartThreshold = c.congestionWindow / 2
  	c.congestionWindow = c.minCongestionWindow
  }
docs: // OnRetransmissionTimeout is called on an retransmission timeout