implement more cubic sender tests

congestion/cubic.go

@@ -215,3 +215,8 @@ func (c *Cubic) CongestionWindowAfterAck(currentCongestionWindow protocol.Packet
 
 	return targetCongestionWindow
 }
+
+// SetNumConnections sets the number of emulated connections
+func (c *Cubic) SetNumConnections(n int) {
+	c.numConnections = n
+}

congestion/cubic_sender.go

@@ -5,11 +5,13 @@ import (
 	"time"
 
 	"github.com/lucas-clemente/quic-go/protocol"
+	"github.com/lucas-clemente/quic-go/utils"
 )
 
 const (
 	maxBurstBytes                                        = 3 * protocol.DefaultTCPMSS
 	defaultMinimumCongestionWindow protocol.PacketNumber = 2
+	renoBeta                       float32               = 0.7 // Reno backoff factor.
 )
 
 type cubicSender struct {
@@ -46,17 +48,27 @@ type cubicSender struct {
 
 	// Maximum number of outstanding packets for tcp.
 	maxTCPCongestionWindow protocol.PacketNumber
+
+	// Number of connections to simulate.
+	numConnections int
+
+	// ACK counter for the Reno implementation.
+	congestionWindowCount uint64
+
+	reno bool
 }
 
 // NewCubicSender makes a new cubic sender
-func NewCubicSender(clock Clock, rttStats *RTTStats, initialCongestionWindow protocol.PacketNumber) SendAlgorithm {
+func NewCubicSender(clock Clock, rttStats *RTTStats, reno bool, initialCongestionWindow, maxCongestionWindow protocol.PacketNumber) SendAlgorithm {
 	return &cubicSender{
 		rttStats:               rttStats,
-		minCongestionWindow:    defaultMinimumCongestionWindow,
 		congestionWindow:       initialCongestionWindow,
-		maxTCPCongestionWindow: protocol.MaxCongestionWindow,
+		minCongestionWindow:    defaultMinimumCongestionWindow,
-		slowstartThreshold:     protocol.MaxCongestionWindow,
+		slowstartThreshold:     maxCongestionWindow,
+		maxTCPCongestionWindow: maxCongestionWindow,
+		numConnections:         defaultNumConnections,
 		cubic:                  NewCubic(clock),
+		reno:                   reno,
 	}
 }
 
@@ -105,6 +117,10 @@ func (c *cubicSender) ExitSlowstart() {
 	c.slowstartThreshold = c.congestionWindow
 }
 
+func (c *cubicSender) SlowstartThreshold() protocol.PacketNumber {
+	return c.slowstartThreshold
+}
+
 // OnCongestionEvent indicates an update to the congestion state, caused either by an incoming
 // ack or loss event timeout.  |rttUpdated| indicates whether a new
 // latest_rtt sample has been taken, |byte_in_flight| the bytes in flight
@@ -159,6 +175,8 @@ func (c *cubicSender) onPacketLost(packetNumber protocol.PacketNumber, lostBytes
 	// TODO(chromium): Separate out all of slow start into a separate class.
 	if c.slowStartLargeReduction && c.InSlowStart() {
 		c.congestionWindow = c.congestionWindow - 1
+	} else if c.reno {
+		c.congestionWindow = protocol.PacketNumber(float32(c.congestionWindow) * c.renoBeta())
 	} else {
 		c.congestionWindow = c.cubic.CongestionWindowAfterPacketLoss(c.congestionWindow)
 	}
@@ -168,6 +186,17 @@ func (c *cubicSender) onPacketLost(packetNumber protocol.PacketNumber, lostBytes
 	}
 	c.slowstartThreshold = c.congestionWindow
 	c.largestSentAtLastCutback = c.largestSentPacketNumber
+	// reset packet count from congestion avoidance mode. We start
+	// counting again when we're out of recovery.
+	c.congestionWindowCount = 0
+}
+
+func (c *cubicSender) renoBeta() float32 {
+	// kNConnectionBeta is the backoff factor after loss for our N-connection
+	// emulation, which emulates the effective backoff of an ensemble of N
+	// TCP-Reno connections on a single loss event. The effective multiplier is
+	// computed as:
+	return (float32(c.numConnections) - 1. + renoBeta) / float32(c.numConnections)
 }
 
 // Called when we receive an ack. Normal TCP tracks how many packets one ack
@@ -187,8 +216,19 @@ func (c *cubicSender) maybeIncreaseCwnd(ackedPacketNumber protocol.PacketNumber,
 		c.congestionWindow++
 		return
 	}
+	if c.reno {
+		// Classic Reno congestion avoidance.
+		c.congestionWindowCount++
+		// Divide by num_connections to smoothly increase the CWND at a faster
+		// rate than conventional Reno.
+		if protocol.PacketNumber(c.congestionWindowCount*uint64(c.numConnections)) >= c.congestionWindow {
+			c.congestionWindow++
+			c.congestionWindowCount = 0
+		}
+	} else {
 		c.congestionWindow = protocol.MinPacketNumber(c.maxTCPCongestionWindow, c.cubic.CongestionWindowAfterAck(c.congestionWindow, c.rttStats.MinRTT()))
 	}
+}
 
 func (c *cubicSender) isCwndLimited(bytesInFlight uint64) bool {
 	congestionWindow := c.GetCongestionWindow()
@@ -209,3 +249,26 @@ func (c *cubicSender) BandwidthEstimate() Bandwidth {
 	}
 	return BandwidthFromDelta(c.GetCongestionWindow(), srtt)
 }
+
+// HybridSlowStart returns the hybrid slow start instance for testing
+func (c *cubicSender) HybridSlowStart() *HybridSlowStart {
+	return &c.hybridSlowStart
+}
+
+// SetNumEmulatedConnections sets the number of emulated connections
+func (c *cubicSender) SetNumEmulatedConnections(n int) {
+	c.numConnections = utils.Max(n, 1)
+	c.cubic.SetNumConnections(c.numConnections)
+}
+
+// OnRetransmissionTimeout is called on an retransmission timeout
+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
+}

congestion/cubic_sender_test.go

@@ -11,6 +11,7 @@ import (
 
 const initialCongestionWindowPackets protocol.PacketNumber = 10
 const defaultWindowTCP = uint64(initialCongestionWindowPackets * protocol.DefaultTCPMSS)
+const renoBeta float32 = 0.7 // Reno backoff factor.
 
 type mockClock time.Time
 
@@ -35,12 +36,13 @@ var _ = Describe("Cubic Sender", func() {
 	BeforeEach(func() {
 		bytesInFlight = 0
 		packetNumber = 1
+		ackedPacketNumber = 0
 		clock = mockClock{}
 		rttStats = congestion.NewRTTStats()
-		sender = congestion.NewCubicSender(&clock, rttStats, initialCongestionWindowPackets)
+		sender = congestion.NewCubicSender(&clock, rttStats, true /*reno*/, initialCongestionWindowPackets, protocol.MaxCongestionWindow)
 	})
 
-	SendAvailableSendWindow := func(packetLength uint64) int {
+	SendAvailableSendWindow := func() int {
 		// Send as long as TimeUntilSend returns Zero.
 		packets_sent := 0
 		can_send := sender.TimeUntilSend(clock.Now(), bytesInFlight) == 0
@@ -68,6 +70,18 @@ var _ = Describe("Cubic Sender", func() {
 		clock.Advance(time.Millisecond)
 	}
 
+	LoseNPackets := func(n int) {
+		packetLength := uint64(protocol.DefaultTCPMSS)
+		var ackedPackets congestion.PacketVector
+		var lostPackets congestion.PacketVector
+		for i := 0; i < n; i++ {
+			ackedPacketNumber++
+			lostPackets = append(lostPackets, congestion.PacketInfo{Number: ackedPacketNumber, Length: packetLength})
+		}
+		sender.OnCongestionEvent(false, bytesInFlight, ackedPackets, lostPackets)
+		bytesInFlight -= uint64(n) * packetLength
+	}
+
 	It("simpler sender", func() {
 		// At startup make sure we are at the default.
 		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
@@ -79,7 +93,7 @@ var _ = Describe("Cubic Sender", func() {
 		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
 
 		// Fill the send window with data, then verify that we can't send.
-		SendAvailableSendWindow(protocol.DefaultTCPMSS)
+		SendAvailableSendWindow()
 		Expect(sender.TimeUntilSend(clock.Now(), sender.GetCongestionWindow())).ToNot(BeZero())
 	})
 
@@ -91,7 +105,7 @@ var _ = Describe("Cubic Sender", func() {
 		// Make sure we can send.
 		Expect(sender.TimeUntilSend(clock.Now(), 0)).To(BeZero())
 
-		SendAvailableSendWindow(protocol.DefaultTCPMSS)
+		SendAvailableSendWindow()
 		for i := 0; i < kNumberOfAcks; i++ {
 			AckNPackets(2)
 		}
@@ -111,7 +125,7 @@ var _ = Describe("Cubic Sender", func() {
 
 		for i := 0; i < kNumberOfAcks; i++ {
 			// Send our full send window.
-			SendAvailableSendWindow(protocol.DefaultTCPMSS)
+			SendAvailableSendWindow()
 			AckNPackets(2)
 		}
 		cwnd := sender.GetCongestionWindow()
@@ -119,4 +133,181 @@ var _ = Describe("Cubic Sender", func() {
 		Expect(sender.BandwidthEstimate()).To(Equal(congestion.BandwidthFromDelta(cwnd, rttStats.SmoothedRTT())))
 	})
 
+	PIt("slow start packet loss", func() {
+		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))
+
+		// Lose a packet to exit slow start.
+		LoseNPackets(1)
+		packets_in_recovery_window := expected_send_window / protocol.DefaultTCPMSS
+
+		// We should now have fallen out of slow start with a reduced window.
+		expected_send_window = uint64(float32(expected_send_window) * renoBeta)
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+
+		// Recovery phase. We need to ack every packet in the recovery window before
+		// we exit recovery.
+		number_of_packets_in_window := expected_send_window / protocol.DefaultTCPMSS
+		AckNPackets(int(packets_in_recovery_window))
+		SendAvailableSendWindow()
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+
+		// We need to ack an entire window before we increase CWND by 1.
+		AckNPackets(int(number_of_packets_in_window) - 2)
+		SendAvailableSendWindow()
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+
+		// Next ack should increase cwnd by 1.
+		AckNPackets(1)
+		expected_send_window += protocol.DefaultTCPMSS
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+
+		// Now RTO and ensure slow start gets reset.
+		Expect(sender.HybridSlowStart().Started()).To(BeTrue())
+		sender.OnRetransmissionTimeout(true)
+		Expect(sender.HybridSlowStart().Started()).To(BeFalse())
+	})
+
+	It("no PRR when less than one packet in flight", func() {
+		SendAvailableSendWindow()
+		LoseNPackets(int(initialCongestionWindowPackets) - 1)
+		AckNPackets(1)
+		// PRR will allow 2 packets for every ack during recovery.
+		Expect(SendAvailableSendWindow()).To(Equal(2))
+		// Simulate abandoning all packets by supplying a bytes_in_flight of 0.
+		// PRR should now allow a packet to be sent, even though prr's state
+		// variables believe it has sent enough packets.
+		Expect(sender.TimeUntilSend(clock.Now(), 0)).To(BeZero())
+	})
+
+	PIt("slow start packet loss PRR", func() {
+		sender.SetNumEmulatedConnections(1)
+		// Test based on the first example in RFC6937.
+		// Ack 10 packets in 5 acks to raise the CWND to 20, as in the example.
+		const kNumberOfAcks = 5
+		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))
+
+		LoseNPackets(1)
+
+		// We should now have fallen out of slow start with a reduced window.
+		send_window_before_loss := expected_send_window
+		expected_send_window = uint64(float32(expected_send_window) * renoBeta)
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+
+		// Testing TCP proportional rate reduction.
+		// We should send packets paced over the received acks for the remaining
+		// outstanding packets. The number of packets before we exit recovery is the
+		// original CWND minus the packet that has been lost and the one which
+		// triggered the loss.
+		remaining_packets_in_recovery := send_window_before_loss/protocol.DefaultTCPMSS - 2
+
+		for i := uint64(0); i < remaining_packets_in_recovery; i++ {
+			AckNPackets(1)
+			SendAvailableSendWindow()
+			Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+		}
+
+		// We need to ack another window before we increase CWND by 1.
+		number_of_packets_in_window := expected_send_window / protocol.DefaultTCPMSS
+		for i := uint64(0); i < number_of_packets_in_window; i++ {
+			AckNPackets(1)
+			Expect(SendAvailableSendWindow()).To(Equal(1))
+			Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+		}
+
+		AckNPackets(1)
+		expected_send_window += protocol.DefaultTCPMSS
+		Expect(sender.GetCongestionWindow()).To(Equal(expected_send_window))
+	})
+
+	It("RTO congestion window", func() {
+		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
+		Expect(sender.SlowstartThreshold()).To(Equal(protocol.MaxCongestionWindow))
+
+		// Expect the window to decrease to the minimum once the RTO fires
+		// and slow start threshold to be set to 1/2 of the CWND.
+		sender.OnRetransmissionTimeout(true)
+		Expect(sender.GetCongestionWindow()).To(Equal(uint64(2 * protocol.DefaultTCPMSS)))
+		Expect(sender.SlowstartThreshold()).To(Equal(protocol.PacketNumber(5)))
+	})
+
+	It("RTO congestion window no retransmission", func() {
+		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
+
+		// Expect the window to remain unchanged if the RTO fires but no
+		// packets are retransmitted.
+		sender.OnRetransmissionTimeout(false)
+		Expect(sender.GetCongestionWindow()).To(Equal(defaultWindowTCP))
+	})
+
+	It("slow start max send window", func() {
+		const kMaxCongestionWindowTCP = 50
+		const kNumberOfAcks = 100
+		sender = congestion.NewCubicSender(&clock, rttStats, false, initialCongestionWindowPackets, kMaxCongestionWindowTCP)
+
+		for i := 0; i < kNumberOfAcks; i++ {
+			// Send our full send window.
+			SendAvailableSendWindow()
+			AckNPackets(2)
+		}
+		expected_send_window := kMaxCongestionWindowTCP * protocol.DefaultTCPMSS
+		Expect(sender.GetCongestionWindow()).To(Equal(uint64(expected_send_window)))
+	})
+
+	It("tcp reno max congestion window", func() {
+		const kMaxCongestionWindowTCP = 50
+		const kNumberOfAcks = 1000
+		sender = congestion.NewCubicSender(&clock, rttStats, false, initialCongestionWindowPackets, kMaxCongestionWindowTCP)
+
+		SendAvailableSendWindow()
+		AckNPackets(2)
+		// Make sure we fall out of slow start.
+		LoseNPackets(1)
+
+		for i := 0; i < kNumberOfAcks; i++ {
+			// Send our full send window.
+			SendAvailableSendWindow()
+			AckNPackets(2)
+		}
+
+		expected_send_window := kMaxCongestionWindowTCP * protocol.DefaultTCPMSS
+		Expect(sender.GetCongestionWindow()).To(Equal(uint64(expected_send_window)))
+	})
+
+	It("tcp cubic max congestion window", func() {
+		const kMaxCongestionWindowTCP = 50
+		// Set to 10000 to compensate for small cubic alpha.
+		const kNumberOfAcks = 10000
+
+		sender = congestion.NewCubicSender(&clock, rttStats, false, initialCongestionWindowPackets, kMaxCongestionWindowTCP)
+
+		SendAvailableSendWindow()
+		AckNPackets(2)
+		// Make sure we fall out of slow start.
+		LoseNPackets(1)
+
+		for i := 0; i < kNumberOfAcks; i++ {
+			// Send our full send window.
+			SendAvailableSendWindow()
+			AckNPackets(2)
+		}
+
+		expected_send_window := kMaxCongestionWindowTCP * protocol.DefaultTCPMSS
+		Expect(sender.GetCongestionWindow()).To(Equal(uint64(expected_send_window)))
+	})
 })

congestion/hybrid_slow_start.go

@@ -98,3 +98,14 @@ func (s *HybridSlowStart) OnPacketAcked(ackedPacketNumber protocol.PacketNumber)
 		s.started = false
 	}
 }
+
+// Started returns true if started
+func (s *HybridSlowStart) Started() bool {
+	return s.started
+}
+
+// Restart the slow start phase
+func (s *HybridSlowStart) Restart() {
+	s.started = false
+	s.hystartFound = false
+}

congestion/interface.go

@@ -12,4 +12,9 @@ type SendAlgorithm interface {
 	GetCongestionWindow() uint64
 	OnCongestionEvent(rttUpdated bool, bytesInFlight uint64, ackedPackets PacketVector, lostPackets PacketVector)
 	BandwidthEstimate() Bandwidth
+	SetNumEmulatedConnections(n int)
+	OnRetransmissionTimeout(packetsRetransmitted bool)
+
+	HybridSlowStart() *HybridSlowStart         // only for testing
+	SlowstartThreshold() protocol.PacketNumber // only for testing
 }

utils/utils.go

@@ -141,6 +141,14 @@ func Max(a, b int) int {
 	return a
 }
 
+// MaxUint32 returns the maximum of two uint32
+func MaxUint32(a, b uint32) uint32 {
+	if a < b {
+		return b
+	}
+	return a
+}
+
 // MaxUint64 returns the maximum of two uint64
 func MaxUint64(a, b uint64) uint64 {
 	if a < b {

utils/utils_test.go

@@ -127,6 +127,10 @@ var _ = Describe("Utils", func() {
 			Expect(Max(5, 7)).To(Equal(7))
 		})
 
+		It("returns the maximum uint32", func() {
+			Expect(MaxUint32(5, 7)).To(Equal(uint32(7)))
+		})
+
 		It("returns the maximum uint64", func() {
 			Expect(MaxUint64(5, 7)).To(Equal(uint64(7)))
 		})