implement cubic sender connection migration

congestion/cubic_sender.go

@@ -21,6 +21,8 @@ type cubicSender struct {
 	stats           connectionStats
 	cubic           *Cubic
 
+	reno bool
+
 	// Track the largest packet that has been sent.
 	largestSentPacketNumber protocol.PacketNumber
 
@@ -55,17 +57,20 @@ type cubicSender struct {
 	// ACK counter for the Reno implementation.
 	congestionWindowCount uint64
 
-	reno bool
+	initialCongestionWindow    protocol.PacketNumber
+	initialMaxCongestionWindow protocol.PacketNumber
 }
 
 // NewCubicSender makes a new cubic sender
-func NewCubicSender(clock Clock, rttStats *RTTStats, reno bool, initialCongestionWindow, maxCongestionWindow protocol.PacketNumber) SendAlgorithm {
+func NewCubicSender(clock Clock, rttStats *RTTStats, reno bool, initialCongestionWindow, initialMaxCongestionWindow protocol.PacketNumber) SendAlgorithm {
 	return &cubicSender{
 		rttStats:                   rttStats,
+		initialCongestionWindow:    initialCongestionWindow,
+		initialMaxCongestionWindow: initialMaxCongestionWindow,
 		congestionWindow:           initialCongestionWindow,
 		minCongestionWindow:        defaultMinimumCongestionWindow,
-		slowstartThreshold:     maxCongestionWindow,
-		maxTCPCongestionWindow: maxCongestionWindow,
+		slowstartThreshold:         initialMaxCongestionWindow,
+		maxTCPCongestionWindow:     initialMaxCongestionWindow,
 		numConnections:             defaultNumConnections,
 		cubic:                      NewCubic(clock),
 		reno:                       reno,
@@ -272,3 +277,18 @@ func (c *cubicSender) OnRetransmissionTimeout(packetsRetransmitted bool) {
 	c.slowstartThreshold = c.congestionWindow / 2
 	c.congestionWindow = c.minCongestionWindow
 }
+
+// OnConnectionMigration is called when the connection is migrated (?)
+func (c *cubicSender) OnConnectionMigration() {
+	c.hybridSlowStart.Restart()
+	c.prr = PrrSender{}
+	c.largestSentPacketNumber = 0
+	c.largestAckedPacketNumber = 0
+	c.largestSentAtLastCutback = 0
+	c.lastCutbackExitedSlowstart = false
+	c.cubic.Reset()
+	c.congestionWindowCount = 0
+	c.congestionWindow = c.initialCongestionWindow
+	c.slowstartThreshold = c.initialMaxCongestionWindow
+	c.maxTCPCongestionWindow = c.initialMaxCongestionWindow
+}

congestion/cubic_sender_test.go

@@ -464,4 +464,36 @@ var _ = Describe("Cubic Sender", func() {
 		expected_send_window += protocol.DefaultTCPMSS
 		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
 	})
+
+	It("reset after connection migration", func() {
+		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
+		Expect(sender.SlowstartThreshold()).To(Equal(protocol.MaxCongestionWindow))
+
+		// Starts with slow start.
+		sender.SetNumEmulatedConnections(1)
+		const kNumberOfAcks = 10
+		for i := 0; i < kNumberOfAcks; i++ {
+			// Send our full send window.
+			SendAvailableSendWindow()
+			AckNPackets(2)
+		}
+		SendAvailableSendWindow()
+		expected_send_window := defaultWindowTCP + (protocol.DefaultTCPMSS * 2 * kNumberOfAcks)
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+
+		// Loses a packet to exit slow start.
+		LoseNPackets(1)
+
+		// We should now have fallen out of slow start with a reduced window. Slow
+		// start threshold is also updated.
+		expected_send_window = uint64(float32(expected_send_window) * renoBeta)
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+		Expect(sender.SlowstartThreshold()).To(Equal(protocol.PacketNumber(expected_send_window / protocol.DefaultTCPMSS)))
+
+		// Resets cwnd and slow start threshold on connection migrations.
+		sender.OnConnectionMigration()
+		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
+		Expect(sender.SlowstartThreshold()).To(Equal(protocol.MaxCongestionWindow))
+		Expect(sender.HybridSlowStart().Started()).To(BeFalse())
+	})
 })

congestion/interface.go

@@ -15,6 +15,7 @@ type SendAlgorithm interface {
 	SetNumEmulatedConnections(n int)
 	OnRetransmissionTimeout(packetsRetransmitted bool)
 	InRecovery() bool
+	OnConnectionMigration()
 
 	HybridSlowStart() *HybridSlowStart         // only for testing
 	SlowstartThreshold() protocol.PacketNumber // only for testing