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// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <cstddef>
#include <cstdint>
#include <map>
#include <memory>
#include <set>
#include <string>
#include <utility>
#include <vector>
#include "quic/core/congestion_control/pacing_sender.h"
#include "quic/core/congestion_control/rtt_stats.h"
#include "quic/core/congestion_control/send_algorithm_interface.h"
#include "quic/core/congestion_control/uber_loss_algorithm.h"
#include "quic/core/proto/cached_network_parameters_proto.h"
#include "quic/core/quic_packets.h"
#include "quic/core/quic_sustained_bandwidth_recorder.h"
#include "quic/core/quic_time.h"
#include "quic/core/quic_transmission_info.h"
#include "quic/core/quic_types.h"
#include "quic/core/quic_unacked_packet_map.h"
#include "quic/platform/api/quic_containers.h"
#include "quic/platform/api/quic_export.h"
#include "common/quiche_circular_deque.h"
namespace quic {
namespace test {
class QuicConnectionPeer;
class QuicSentPacketManagerPeer;
} // namespace test
class QuicClock;
class QuicConfig;
struct QuicConnectionStats;
// Class which tracks the set of packets sent on a QUIC connection and contains
// a send algorithm to decide when to send new packets. It keeps track of any
// retransmittable data associated with each packet. If a packet is
// retransmitted, it will keep track of each version of a packet so that if a
// previous transmission is acked, the data will not be retransmitted.
class QUIC_EXPORT_PRIVATE QuicSentPacketManager {
// Interface which gets callbacks from the QuicSentPacketManager at
// interesting points. Implementations must not mutate the state of
// the packet manager or connection as a result of these callbacks.
class QUIC_EXPORT_PRIVATE DebugDelegate {
virtual ~DebugDelegate() {}
// Called when a spurious retransmission is detected.
virtual void OnSpuriousPacketRetransmission(
TransmissionType /*transmission_type*/,
QuicByteCount /*byte_size*/) {}
virtual void OnIncomingAck(QuicPacketNumber /*ack_packet_number*/,
EncryptionLevel /*ack_decrypted_level*/,
const QuicAckFrame& /*ack_frame*/,
QuicTime /*ack_receive_time*/,
QuicPacketNumber /*largest_observed*/,
bool /*rtt_updated*/,
QuicPacketNumber /*least_unacked_sent_packet*/) {
virtual void OnPacketLoss(QuicPacketNumber /*lost_packet_number*/,
EncryptionLevel /*encryption_level*/,
TransmissionType /*transmission_type*/,
QuicTime /*detection_time*/) {}
virtual void OnApplicationLimited() {}
virtual void OnAdjustNetworkParameters(QuicBandwidth /*bandwidth*/,
QuicTime::Delta /*rtt*/,
QuicByteCount /*old_cwnd*/,
QuicByteCount /*new_cwnd*/) {}
virtual void OnOvershootingDetected() {}
// Interface which gets callbacks from the QuicSentPacketManager when
// network-related state changes. Implementations must not mutate the
// state of the packet manager as a result of these callbacks.
class QUIC_EXPORT_PRIVATE NetworkChangeVisitor {
virtual ~NetworkChangeVisitor() {}
// Called when congestion window or RTT may have changed.
virtual void OnCongestionChange() = 0;
// Called when the Path MTU may have increased.
virtual void OnPathMtuIncreased(QuicPacketLength packet_size) = 0;
// The retransmission timer is a single timer which switches modes depending
// upon connection state.
enum RetransmissionTimeoutMode {
// A conventional TCP style RTO.
// A tail loss probe. By default, QUIC sends up to two before RTOing.
// Retransmission of handshake packets prior to handshake completion.
// Re-invoke the loss detection when a packet is not acked before the
// loss detection algorithm expects.
// A probe timeout. At least one probe packet must be sent when timer
// expires.
QuicSentPacketManager(Perspective perspective,
const QuicClock* clock,
QuicRandom* random,
QuicConnectionStats* stats,
CongestionControlType congestion_control_type);
QuicSentPacketManager(const QuicSentPacketManager&) = delete;
QuicSentPacketManager& operator=(const QuicSentPacketManager&) = delete;
virtual ~QuicSentPacketManager();
virtual void SetFromConfig(const QuicConfig& config);
void ReserveUnackedPacketsInitialCapacity(int initial_capacity) {
void ApplyConnectionOptions(const QuicTagVector& connection_options);
// Pass the CachedNetworkParameters to the send algorithm.
void ResumeConnectionState(
const CachedNetworkParameters& cached_network_params,
bool max_bandwidth_resumption);
void SetMaxPacingRate(QuicBandwidth max_pacing_rate) {
QuicBandwidth MaxPacingRate() const {
return pacing_sender_.max_pacing_rate();
// Called to mark the handshake state complete, and all handshake packets are
// neutered.
// TODO(fayang): Rename this function to OnHandshakeComplete.
void SetHandshakeConfirmed();
// Requests retransmission of all unacked 0-RTT packets.
// Only 0-RTT encrypted packets will be retransmitted. This can happen,
// for example, when a CHLO has been rejected and the previously encrypted
// data needs to be encrypted with a new key.
void MarkZeroRttPacketsForRetransmission();
// Request retransmission of all unacked INITIAL packets.
void MarkInitialPacketsForRetransmission();
// Notify the sent packet manager of an external network measurement or
// prediction for either |bandwidth| or |rtt|; either can be empty.
void AdjustNetworkParameters(
const SendAlgorithmInterface::NetworkParams& params);
void SetLossDetectionTuner(
std::unique_ptr<LossDetectionTunerInterface> tuner);
void OnConfigNegotiated();
void OnConnectionClosed();
// Retransmits the oldest pending packet there is still a tail loss probe
// pending. Invoked after OnRetransmissionTimeout.
bool MaybeRetransmitTailLossProbe();
// Retransmits the oldest pending packet.
bool MaybeRetransmitOldestPacket(TransmissionType type);
// Removes the retransmittable frames from all unencrypted packets to ensure
// they don't get retransmitted.
void NeuterUnencryptedPackets();
// Returns true if there's outstanding crypto data.
bool HasUnackedCryptoPackets() const {
return unacked_packets_.HasPendingCryptoPackets();
// Returns true if there are packets in flight expecting to be acknowledged.
bool HasInFlightPackets() const {
return unacked_packets_.HasInFlightPackets();
// Returns the smallest packet number of a serialized packet which has not
// been acked by the peer.
QuicPacketNumber GetLeastUnacked() const {
return unacked_packets_.GetLeastUnacked();
// Called when we have sent bytes to the peer. This informs the manager both
// the number of bytes sent and if they were retransmitted and if this packet
// is used for rtt measuring. Returns true if the sender should reset the
// retransmission timer.
bool OnPacketSent(SerializedPacket* mutable_packet,
QuicTime sent_time,
TransmissionType transmission_type,
HasRetransmittableData has_retransmittable_data,
bool measure_rtt);
bool CanSendAckFrequency() const;
QuicAckFrequencyFrame GetUpdatedAckFrequencyFrame() const;
// Called when the retransmission timer expires and returns the retransmission
// mode.
RetransmissionTimeoutMode OnRetransmissionTimeout();
// Calculate the time until we can send the next packet to the wire.
// Note 1: When kUnknownWaitTime is returned, there is no need to poll
// TimeUntilSend again until we receive an OnIncomingAckFrame event.
// Note 2: Send algorithms may or may not use |retransmit| in their
// calculations.
QuicTime::Delta TimeUntilSend(QuicTime now) const;
// Returns the current delay for the retransmission timer, which may send
// either a tail loss probe or do a full RTO. Returns QuicTime::Zero() if
// there are no retransmittable packets.
const QuicTime GetRetransmissionTime() const;
// Returns the current delay for the path degrading timer, which is used to
// notify the session that this connection is degrading.
const QuicTime::Delta GetPathDegradingDelay() const;
// Returns the current delay for detecting network blackhole.
const QuicTime::Delta GetNetworkBlackholeDelay(
int8_t num_rtos_for_blackhole_detection) const;
// Returns the delay before reducing max packet size. This delay is guranteed
// to be smaller than the network blackhole delay.
QuicTime::Delta GetMtuReductionDelay(
int8_t num_rtos_for_blackhole_detection) const;
const RttStats* GetRttStats() const { return &rtt_stats_; }
void SetRttStats(const RttStats& rtt_stats) {
// Returns the estimated bandwidth calculated by the congestion algorithm.
QuicBandwidth BandwidthEstimate() const {
return send_algorithm_->BandwidthEstimate();
const QuicSustainedBandwidthRecorder* SustainedBandwidthRecorder() const {
return &sustained_bandwidth_recorder_;
// Returns the size of the current congestion window in number of
// kDefaultTCPMSS-sized segments. Note, this is not the *available* window.
// Some send algorithms may not use a congestion window and will return 0.
QuicPacketCount GetCongestionWindowInTcpMss() const {
return send_algorithm_->GetCongestionWindow() / kDefaultTCPMSS;
// Returns the number of packets of length |max_packet_length| which fit in
// the current congestion window. More packets may end up in flight if the
// congestion window has been recently reduced, of if non-full packets are
// sent.
QuicPacketCount EstimateMaxPacketsInFlight(
QuicByteCount max_packet_length) const {
return send_algorithm_->GetCongestionWindow() / max_packet_length;
// Returns the size of the current congestion window size in bytes.
QuicByteCount GetCongestionWindowInBytes() const {
return send_algorithm_->GetCongestionWindow();
QuicBandwidth GetPacingRate() const {
return send_algorithm_->PacingRate(GetBytesInFlight());
// Returns the size of the slow start congestion window in nume of 1460 byte
// TCP segments, aka ssthresh. Some send algorithms do not define a slow
// start threshold and will return 0.
QuicPacketCount GetSlowStartThresholdInTcpMss() const {
return send_algorithm_->GetSlowStartThreshold() / kDefaultTCPMSS;
// Return the total time spent in slow start so far. If the sender is
// currently in slow start, the return value will include the duration between
// the most recent entry to slow start and now.
// Only implemented for BBR. Return QuicTime::Delta::Infinite() for other
// congestion controllers.
QuicTime::Delta GetSlowStartDuration() const;
// Returns debugging information about the state of the congestion controller.
std::string GetDebugState() const;
// Returns the number of bytes that are considered in-flight, i.e. not lost or
// acknowledged.
QuicByteCount GetBytesInFlight() const {
return unacked_packets_.bytes_in_flight();
// Called when peer address changes. Must be called IFF the address change is
// not NAT rebinding. If reset_send_algorithm is true, switch to a new send
// algorithm object and retransmit all the in-flight packets. Return the send
// algorithm object used on the previous path.
std::unique_ptr<SendAlgorithmInterface> OnConnectionMigration(
bool reset_send_algorithm);
// Called when an ack frame is initially parsed.
void OnAckFrameStart(QuicPacketNumber largest_acked,
QuicTime::Delta ack_delay_time,
QuicTime ack_receive_time);
// Called when ack range [start, end) is received. Populates packets_acked_
// with newly acked packets.
void OnAckRange(QuicPacketNumber start, QuicPacketNumber end);
// Called when a timestamp is processed. If it's present in packets_acked_,
// the timestamp field is set. Otherwise, the timestamp is ignored.
void OnAckTimestamp(QuicPacketNumber packet_number, QuicTime timestamp);
// Called when an ack frame is parsed completely.
AckResult OnAckFrameEnd(QuicTime ack_receive_time,
QuicPacketNumber ack_packet_number,
EncryptionLevel ack_decrypted_level);
void EnableMultiplePacketNumberSpacesSupport();
void SetDebugDelegate(DebugDelegate* debug_delegate);
void SetPacingAlarmGranularity(QuicTime::Delta alarm_granularity) {
QuicPacketNumber GetLargestObserved() const {
return unacked_packets_.largest_acked();
QuicPacketNumber GetLargestAckedPacket(
EncryptionLevel decrypted_packet_level) const;
QuicPacketNumber GetLargestSentPacket() const {
return unacked_packets_.largest_sent_packet();
// Returns the lowest of the largest acknowledged packet and the least
// unacked packet. This is designed to be used when computing the packet
// number length to send.
QuicPacketNumber GetLeastPacketAwaitedByPeer(
EncryptionLevel encryption_level) const;
QuicPacketNumber GetLargestPacketPeerKnowsIsAcked(
EncryptionLevel decrypted_packet_level) const;
void SetNetworkChangeVisitor(NetworkChangeVisitor* visitor) {
network_change_visitor_ = visitor;
bool InSlowStart() const { return send_algorithm_->InSlowStart(); }
size_t GetConsecutiveRtoCount() const { return consecutive_rto_count_; }
size_t GetConsecutiveTlpCount() const { return consecutive_tlp_count_; }
size_t GetConsecutivePtoCount() const { return consecutive_pto_count_; }
void OnApplicationLimited();
const SendAlgorithmInterface* GetSendAlgorithm() const {
return send_algorithm_.get();
void SetSessionNotifier(SessionNotifierInterface* session_notifier) {
NextReleaseTimeResult GetNextReleaseTime() const;
QuicPacketCount initial_congestion_window() const {
return initial_congestion_window_;
QuicPacketNumber largest_packet_peer_knows_is_acked() const {
return largest_packet_peer_knows_is_acked_;
size_t pending_timer_transmission_count() const {
return pending_timer_transmission_count_;
QuicTime::Delta peer_max_ack_delay() const { return peer_max_ack_delay_; }
void set_peer_max_ack_delay(QuicTime::Delta peer_max_ack_delay) {
// The delayed ack time should never be more than one half the min RTO time.
QUICHE_DCHECK_LE(peer_max_ack_delay, (min_rto_timeout_ * 0.5));
peer_max_ack_delay_ = peer_max_ack_delay;
const QuicUnackedPacketMap& unacked_packets() const {
return unacked_packets_;
const UberLossAlgorithm* uber_loss_algorithm() const {
return &uber_loss_algorithm_;
// Sets the send algorithm to the given congestion control type and points the
// pacing sender at |send_algorithm_|. Can be called any number of times.
void SetSendAlgorithm(CongestionControlType congestion_control_type);
// Sets the send algorithm to |send_algorithm| and points the pacing sender at
// |send_algorithm_|. Takes ownership of |send_algorithm|. Can be called any
// number of times.
// Setting the send algorithm once the connection is underway is dangerous.
void SetSendAlgorithm(SendAlgorithmInterface* send_algorithm);
// Sends up to max_probe_packets_per_pto_ probe packets.
void MaybeSendProbePackets();
// Called to adjust pending_timer_transmission_count_ accordingly.
void AdjustPendingTimerTransmissions();
// Called to disable HANDSHAKE_MODE, and only PTO and LOSS modes are used.
// Also enable IETF loss detection.
void EnableIetfPtoAndLossDetection();
// Called to set the start point of doing exponential backoff when calculating
// PTO timeout.
void StartExponentialBackoffAfterNthPto(
size_t exponential_backoff_start_point);
// Called to retransmit in flight packet of |space| if any.
void RetransmitDataOfSpaceIfAny(PacketNumberSpace space);
// Returns true if |timeout| is less than 3 * RTO/PTO delay.
bool IsLessThanThreePTOs(QuicTime::Delta timeout) const;
// Returns current PTO delay.
QuicTime::Delta GetPtoDelay() const;
bool supports_multiple_packet_number_spaces() const {
return unacked_packets_.supports_multiple_packet_number_spaces();
bool pto_enabled() const { return pto_enabled_; }
bool handshake_mode_disabled() const { return handshake_mode_disabled_; }
bool skip_packet_number_for_pto() const {
return skip_packet_number_for_pto_;
bool zero_rtt_packet_acked() const { return zero_rtt_packet_acked_; }
bool one_rtt_packet_acked() const { return one_rtt_packet_acked_; }
void OnUserAgentIdKnown() { loss_algorithm_->OnUserAgentIdKnown(); }
// Gets the earliest in flight packet sent time to calculate PTO. Also
// updates |packet_number_space| if a PTO timer should be armed.
QuicTime GetEarliestPacketSentTimeForPto(
PacketNumberSpace* packet_number_space) const;
void set_num_ptos_for_path_degrading(int num_ptos_for_path_degrading) {
num_ptos_for_path_degrading_ = num_ptos_for_path_degrading;
// Sets the initial RTT of the connection.
void SetInitialRtt(QuicTime::Delta rtt);
friend class test::QuicConnectionPeer;
friend class test::QuicSentPacketManagerPeer;
// Returns the current retransmission mode.
RetransmissionTimeoutMode GetRetransmissionMode() const;
// Retransmits all crypto stream packets.
void RetransmitCryptoPackets();
// Retransmits two packets for an RTO and removes any non-retransmittable
// packets from flight.
void RetransmitRtoPackets();
// Returns the timeout for retransmitting crypto handshake packets.
const QuicTime::Delta GetCryptoRetransmissionDelay() const;
// Calls GetTailLossProbeDelay() with values from the current state of this
// packet manager as its params.
const QuicTime::Delta GetTailLossProbeDelay() const;
// Calls GetRetransmissionDelay() with values from the current state of this
// packet manager as its params.
const QuicTime::Delta GetRetransmissionDelay() const;
// Returns the probe timeout.
const QuicTime::Delta GetProbeTimeoutDelay(PacketNumberSpace space) const;
// Update the RTT if the ack is for the largest acked packet number.
// Returns true if the rtt was updated.
bool MaybeUpdateRTT(QuicPacketNumber largest_acked,
QuicTime::Delta ack_delay_time,
QuicTime ack_receive_time);
// Invokes the loss detection algorithm and loses and retransmits packets if
// necessary.
void InvokeLossDetection(QuicTime time);
// Invokes OnCongestionEvent if |rtt_updated| is true, there are pending acks,
// or pending losses. Clears pending acks and pending losses afterwards.
// |prior_in_flight| is the number of bytes in flight before the losses or
// acks, |event_time| is normally the timestamp of the ack packet which caused
// the event, although it can be the time at which loss detection was
// triggered.
void MaybeInvokeCongestionEvent(bool rtt_updated,
QuicByteCount prior_in_flight,
QuicTime event_time);
// Removes the retransmittability and in flight properties from the packet at
// |info| due to receipt by the peer.
void MarkPacketHandled(QuicPacketNumber packet_number,
QuicTransmissionInfo* info,
QuicTime ack_receive_time,
QuicTime::Delta ack_delay_time,
QuicTime receive_timestamp);
// Request that |packet_number| be retransmitted after the other pending
// retransmissions. Does not add it to the retransmissions if it's already
// a pending retransmission. Do not reuse iterator of the underlying
// unacked_packets_ after calling this function as it can be invalidated.
void MarkForRetransmission(QuicPacketNumber packet_number,
TransmissionType transmission_type);
// Performs whatever work is need to retransmit the data correctly, either
// by retransmitting the frames directly or by notifying that the frames
// are lost.
void HandleRetransmission(TransmissionType transmission_type,
QuicTransmissionInfo* transmission_info);
// Called after packets have been marked handled with last received ack frame.
void PostProcessNewlyAckedPackets(QuicPacketNumber ack_packet_number,
EncryptionLevel ack_decrypted_level,
const QuicAckFrame& ack_frame,
QuicTime ack_receive_time,
bool rtt_updated,
QuicByteCount prior_bytes_in_flight);
// Notify observers that packet with QuicTransmissionInfo |info| is a spurious
// retransmission. It is caller's responsibility to guarantee the packet with
// QuicTransmissionInfo |info| is a spurious retransmission before calling
// this function.
void RecordOneSpuriousRetransmission(const QuicTransmissionInfo& info);
// Called when handshake is confirmed to remove the retransmittable frames
// from all packets of HANDSHAKE_DATA packet number space to ensure they don't
// get retransmitted and will eventually be removed from unacked packets map.
void NeuterHandshakePackets();
// Indicates whether including peer_max_ack_delay_ when calculating PTO
// timeout.
bool ShouldAddMaxAckDelay(PacketNumberSpace space) const;
// A helper function to return total delay of |num_timeouts| retransmission
// timeout with TLP and RTO mode.
QuicTime::Delta GetNConsecutiveRetransmissionTimeoutDelay(
int num_timeouts) const;
// Returns true if peer has finished address validation, such that
// retransmission timer is not armed if there is no packets in flight.
bool PeerCompletedAddressValidation() const;
// Called when an AckFrequencyFrame is sent.
void OnAckFrequencyFrameSent(
const QuicAckFrequencyFrame& ack_frequency_frame);
// Called when an AckFrequencyFrame is acked.
void OnAckFrequencyFrameAcked(
const QuicAckFrequencyFrame& ack_frequency_frame);
// Newly serialized retransmittable packets are added to this map, which
// contains owning pointers to any contained frames. If a packet is
// retransmitted, this map will contain entries for both the old and the new
// packet. The old packet's retransmittable frames entry will be nullptr,
// while the new packet's entry will contain the frames to retransmit.
// If the old packet is acked before the new packet, then the old entry will
// be removed from the map and the new entry's retransmittable frames will be
// set to nullptr.
QuicUnackedPacketMap unacked_packets_;
const QuicClock* clock_;
QuicRandom* random_;
QuicConnectionStats* stats_;
DebugDelegate* debug_delegate_;
NetworkChangeVisitor* network_change_visitor_;
QuicPacketCount initial_congestion_window_;
RttStats rtt_stats_;
std::unique_ptr<SendAlgorithmInterface> send_algorithm_;
// Not owned. Always points to |uber_loss_algorithm_| outside of tests.
LossDetectionInterface* loss_algorithm_;
UberLossAlgorithm uber_loss_algorithm_;
// Tracks the first RTO packet. If any packet before that packet gets acked,
// it indicates the RTO was spurious and should be reversed(F-RTO).
QuicPacketNumber first_rto_transmission_;
// Number of times the RTO timer has fired in a row without receiving an ack.
size_t consecutive_rto_count_;
// Number of times the tail loss probe has been sent.
size_t consecutive_tlp_count_;
// Number of times the crypto handshake has been retransmitted.
size_t consecutive_crypto_retransmission_count_;
// Number of pending transmissions of TLP, RTO, or crypto packets.
size_t pending_timer_transmission_count_;
// Maximum number of tail loss probes to send before firing an RTO.
size_t max_tail_loss_probes_;
// Maximum number of packets to send upon RTO.
QuicPacketCount max_rto_packets_;
// If true, send the TLP at 0.5 RTT.
// TODO(renjietang): remove it once quic_deprecate_tlpr flag is deprecated.
bool enable_half_rtt_tail_loss_probe_;
bool using_pacing_;
// If true, use the new RTO with loss based CWND reduction instead of the send
// algorithms's OnRetransmissionTimeout to reduce the congestion window.
bool use_new_rto_;
// If true, use a more conservative handshake retransmission policy.
bool conservative_handshake_retransmits_;
// The minimum TLP timeout.
QuicTime::Delta min_tlp_timeout_;
// The minimum RTO.
QuicTime::Delta min_rto_timeout_;
// Vectors packets acked and lost as a result of the last congestion event.
AckedPacketVector packets_acked_;
LostPacketVector packets_lost_;
// Largest newly acknowledged packet.
QuicPacketNumber largest_newly_acked_;
// Largest packet in bytes ever acknowledged.
QuicPacketLength largest_mtu_acked_;
// Replaces certain calls to |send_algorithm_| when |using_pacing_| is true.
// Calls into |send_algorithm_| for the underlying congestion control.
PacingSender pacing_sender_;
// Indicates whether handshake is finished. This is purely used to determine
// retransmission mode. DONOT use this to infer handshake state.
bool handshake_finished_;
// Records bandwidth from server to client in normal operation, over periods
// of time with no loss events.
QuicSustainedBandwidthRecorder sustained_bandwidth_recorder_;
// The largest acked value that was sent in an ack, which has then been acked.
QuicPacketNumber largest_packet_peer_knows_is_acked_;
// The largest acked value that was sent in an ack, which has then been acked
// for per packet number space. Only used when connection supports multiple
// packet number spaces.
// The maximum ACK delay time that the peer might uses. Initialized to be the
// same as local_max_ack_delay_, may be changed via transport parameter
// negotiation or subsequently by AckFrequencyFrame.
QuicTime::Delta peer_max_ack_delay_;
// Peer sends min_ack_delay in TransportParameter to advertise its support for
// AckFrequencyFrame.
QuicTime::Delta peer_min_ack_delay_ = QuicTime::Delta::Infinite();
// Use smoothed RTT for computing max_ack_delay in AckFrequency frame.
bool use_smoothed_rtt_in_ack_delay_ = false;
// The history of outstanding max_ack_delays sent to peer. Outstanding means
// a max_ack_delay is sent as part of the last acked AckFrequencyFrame or
// an unacked AckFrequencyFrame after that.
std::pair<QuicTime::Delta, /*sequence_number=*/uint64_t>>
// Latest received ack frame.
QuicAckFrame last_ack_frame_;
// Record whether RTT gets updated by last largest acked..
bool rtt_updated_;
// A reverse iterator of last_ack_frame_.packets. This is reset in
// OnAckRangeStart, and gradually moves in OnAckRange..
PacketNumberQueue::const_reverse_iterator acked_packets_iter_;
// Indicates whether PTO mode has been enabled. PTO mode unifies TLP and RTO
// modes.
bool pto_enabled_;
// Maximum number of probes to send when PTO fires.
size_t max_probe_packets_per_pto_;
// Number of times the PTO timer has fired in a row without receiving an ack.
size_t consecutive_pto_count_;
// True if HANDSHAKE mode has been disabled.
bool handshake_mode_disabled_;
// If true, skip packet number before sending the last PTO retransmission.
bool skip_packet_number_for_pto_;
// If true, always include peer_max_ack_delay_ when calculating PTO timeout.
bool always_include_max_ack_delay_for_pto_timeout_;
// When calculating PTO timeout, the start point of doing exponential backoff.
// For example, 0 : always do exponential backoff. n : do exponential backoff
// since nth PTO.
size_t pto_exponential_backoff_start_point_;
// The multiplier of rttvar when calculating PTO timeout.
int pto_rttvar_multiplier_;
// Number of PTOs similar to TLPs.
size_t num_tlp_timeout_ptos_;
// True if any ENCRYPTION_HANDSHAKE packet gets acknowledged.
bool handshake_packet_acked_;
// True if any 0-RTT packet gets acknowledged.
bool zero_rtt_packet_acked_;
// True if any 1-RTT packet gets acknowledged.
bool one_rtt_packet_acked_;
// If > 0, arm the 1st PTO with max of earliest in flight sent time + PTO
// delay and multiplier * srtt from last in flight packet.
float first_pto_srtt_multiplier_;
// If true, use standard deviation (instead of mean deviation) when
// calculating PTO timeout.
bool use_standard_deviation_for_pto_;
// The multiplier for caculating PTO timeout before any RTT sample is
// available.
float pto_multiplier_without_rtt_samples_;
// The number of PTOs needed for path degrading alarm. If equals to 0, the
// traditional path degrading mechanism will be used.
int num_ptos_for_path_degrading_;
// If true, do not use PING only packets for RTT measurement or congestion
// control.
bool ignore_pings_;
// Whether to ignore the ack_delay in received ACKs.
bool ignore_ack_delay_;
} // namespace quic