Adding upstream version 0.12.1+dfsg.upstream/0.12.1+dfsgupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1489 insertions, 0 deletions

diff --git a/lib/ngtcp2_bbr2.c b/lib/ngtcp2_bbr2.c
new file mode 100644
index 0000000..508ab55
--- /dev/null
+++ b/lib/ngtcp2_bbr2.c
@@ -0,0 +1,1489 @@
+/*
+ * ngtcp2
+ *
+ * Copyright (c) 2021 ngtcp2 contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include "ngtcp2_bbr2.h"
+
+#include <assert.h>
+
+#include "ngtcp2_log.h"
+#include "ngtcp2_macro.h"
+#include "ngtcp2_mem.h"
+#include "ngtcp2_rcvry.h"
+#include "ngtcp2_rst.h"
+
+#define NGTCP2_BBR_MAX_BW_FILTERLEN 2
+
+#define NGTCP2_BBR_EXTRA_ACKED_FILTERLEN 10
+
+#define NGTCP2_BBR_STARTUP_PACING_GAIN ((double)2.77)
+
+#define NGTCP2_BBR_STARTUP_CWND_GAIN 2
+
+#define NGTCP2_BBR_PROBE_RTT_CWND_GAIN ((double)0.5)
+
+#define NGTCP2_BBR_BETA_NUMER 7
+#define NGTCP2_BBR_BETA_DENOM 10
+
+#define NGTCP2_BBR_LOSS_THRESH_NUMER 2
+#define NGTCP2_BBR_LOSS_THRESH_DENOM 100
+
+#define NGTCP2_BBR_HEADROOM_NUMER 15
+#define NGTCP2_BBR_HEADROOM_DENOM 100
+
+#define NGTCP2_BBR_PROBE_RTT_INTERVAL (5 * NGTCP2_SECONDS)
+#define NGTCP2_BBR_MIN_RTT_FILTERLEN (10 * NGTCP2_SECONDS)
+
+#define NGTCP2_BBR_PROBE_RTT_DURATION (200 * NGTCP2_MILLISECONDS)
+
+#define NGTCP2_BBR_PACING_MARGIN_PERCENT 1
+
+static void bbr_on_init(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                        ngtcp2_tstamp initial_ts);
+
+static void bbr_on_transmit(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                            ngtcp2_tstamp ts);
+
+static void bbr_reset_congestion_signals(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_reset_lower_bounds(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_init_round_counting(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_init_full_pipe(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_init_pacing_rate(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat);
+
+static void bbr_set_pacing_rate_with_gain(ngtcp2_bbr2_cc *bbr,
+                                          ngtcp2_conn_stat *cstat,
+                                          double pacing_gain);
+
+static void bbr_set_pacing_rate(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat);
+
+static void bbr_enter_startup(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_check_startup_done(ngtcp2_bbr2_cc *bbr,
+                                   const ngtcp2_cc_ack *ack);
+
+static void bbr_update_on_ack(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                              const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
+
+static void bbr_update_model_and_state(ngtcp2_bbr2_cc *cc,
+                                       ngtcp2_conn_stat *cstat,
+                                       const ngtcp2_cc_ack *ack,
+                                       ngtcp2_tstamp ts);
+
+static void bbr_update_control_parameters(ngtcp2_bbr2_cc *cc,
+                                          ngtcp2_conn_stat *cstat,
+                                          const ngtcp2_cc_ack *ack);
+
+static void bbr_update_on_loss(ngtcp2_bbr2_cc *cc, ngtcp2_conn_stat *cstat,
+                               const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts);
+
+static void bbr_update_latest_delivery_signals(ngtcp2_bbr2_cc *bbr,
+                                               ngtcp2_conn_stat *cstat);
+
+static void bbr_advance_latest_delivery_signals(ngtcp2_bbr2_cc *bbr,
+                                                ngtcp2_conn_stat *cstat);
+
+static void bbr_update_congestion_signals(ngtcp2_bbr2_cc *bbr,
+                                          ngtcp2_conn_stat *cstat,
+                                          const ngtcp2_cc_ack *ack);
+
+static void bbr_adapt_lower_bounds_from_congestion(ngtcp2_bbr2_cc *bbr,
+                                                   ngtcp2_conn_stat *cstat);
+
+static void bbr_init_lower_bounds(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat);
+
+static void bbr_loss_lower_bounds(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_bound_bw_for_model(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_update_max_bw(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                              const ngtcp2_cc_ack *ack);
+
+static void bbr_update_round(ngtcp2_bbr2_cc *bbr, const ngtcp2_cc_ack *ack);
+
+static void bbr_start_round(ngtcp2_bbr2_cc *bbr);
+
+static int bbr_is_in_probe_bw_state(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_update_ack_aggregation(ngtcp2_bbr2_cc *bbr,
+                                       ngtcp2_conn_stat *cstat,
+                                       const ngtcp2_cc_ack *ack,
+                                       ngtcp2_tstamp ts);
+
+static void bbr_enter_drain(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_check_drain(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                            ngtcp2_tstamp ts);
+
+static void bbr_enter_probe_bw(ngtcp2_bbr2_cc *bbr, ngtcp2_tstamp ts);
+
+static void bbr_start_probe_bw_down(ngtcp2_bbr2_cc *bbr, ngtcp2_tstamp ts);
+
+static void bbr_start_probe_bw_cruise(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_start_probe_bw_refill(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_start_probe_bw_up(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                  ngtcp2_tstamp ts);
+
+static void bbr_update_probe_bw_cycle_phase(ngtcp2_bbr2_cc *bbr,
+                                            ngtcp2_conn_stat *cstat,
+                                            const ngtcp2_cc_ack *ack,
+                                            ngtcp2_tstamp ts);
+
+static int bbr_check_time_to_cruise(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_conn_stat *cstat, ngtcp2_tstamp ts);
+
+static int bbr_has_elapsed_in_phase(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_duration interval, ngtcp2_tstamp ts);
+
+static uint64_t bbr_inflight_with_headroom(ngtcp2_bbr2_cc *bbr,
+                                           ngtcp2_conn_stat *cstat);
+
+static void bbr_raise_inflight_hi_slope(ngtcp2_bbr2_cc *bbr,
+                                        ngtcp2_conn_stat *cstat);
+
+static void bbr_probe_inflight_hi_upward(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat,
+                                         const ngtcp2_cc_ack *ack);
+
+static void bbr_adapt_upper_bounds(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                   const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
+
+static int bbr_check_time_to_probe_bw(ngtcp2_bbr2_cc *bbr,
+                                      ngtcp2_conn_stat *cstat,
+                                      ngtcp2_tstamp ts);
+
+static void bbr_pick_probe_wait(ngtcp2_bbr2_cc *bbr);
+
+static int bbr_is_reno_coexistence_probe_time(ngtcp2_bbr2_cc *bbr,
+                                              ngtcp2_conn_stat *cstat);
+
+static uint64_t bbr_target_inflight(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_conn_stat *cstat);
+
+static int bbr_check_inflight_too_high(ngtcp2_bbr2_cc *bbr,
+                                       ngtcp2_conn_stat *cstat,
+                                       ngtcp2_tstamp ts);
+
+static int is_inflight_too_high(const ngtcp2_rs *rs);
+
+static void bbr_handle_inflight_too_high(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat,
+                                         const ngtcp2_rs *rs, ngtcp2_tstamp ts);
+
+static void bbr_handle_lost_packet(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                   const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts);
+
+static uint64_t bbr_inflight_hi_from_lost_packet(ngtcp2_bbr2_cc *bbr,
+                                                 const ngtcp2_rs *rs,
+                                                 const ngtcp2_cc_pkt *pkt);
+
+static void bbr_update_min_rtt(ngtcp2_bbr2_cc *bbr, const ngtcp2_cc_ack *ack,
+                               ngtcp2_tstamp ts);
+
+static void bbr_check_probe_rtt(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                ngtcp2_tstamp ts);
+
+static void bbr_enter_probe_rtt(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_handle_probe_rtt(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                 ngtcp2_tstamp ts);
+
+static void bbr_check_probe_rtt_done(ngtcp2_bbr2_cc *bbr,
+                                     ngtcp2_conn_stat *cstat, ngtcp2_tstamp ts);
+
+static void bbr_mark_connection_app_limited(ngtcp2_bbr2_cc *bbr,
+                                            ngtcp2_conn_stat *cstat);
+
+static void bbr_exit_probe_rtt(ngtcp2_bbr2_cc *bbr, ngtcp2_tstamp ts);
+
+static void bbr_handle_restart_from_idle(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat,
+                                         ngtcp2_tstamp ts);
+
+static uint64_t bbr_bdp_multiple(ngtcp2_bbr2_cc *bbr, uint64_t bw, double gain);
+
+static uint64_t bbr_quantization_budget(ngtcp2_bbr2_cc *bbr,
+                                        ngtcp2_conn_stat *cstat,
+                                        uint64_t inflight);
+
+static uint64_t bbr_inflight(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                             uint64_t bw, double gain);
+
+static void bbr_update_max_inflight(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_conn_stat *cstat);
+
+static void bbr_update_offload_budget(ngtcp2_bbr2_cc *bbr,
+                                      ngtcp2_conn_stat *cstat);
+
+static uint64_t min_pipe_cwnd(size_t max_udp_payload_size);
+
+static void bbr_advance_max_bw_filter(ngtcp2_bbr2_cc *bbr);
+
+static void bbr_modulate_cwnd_for_recovery(ngtcp2_bbr2_cc *bbr,
+                                           ngtcp2_conn_stat *cstat,
+                                           const ngtcp2_cc_ack *ack);
+
+static void bbr_save_cwnd(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat);
+
+static void bbr_restore_cwnd(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat);
+
+static uint64_t bbr_probe_rtt_cwnd(ngtcp2_bbr2_cc *bbr,
+                                   ngtcp2_conn_stat *cstat);
+
+static void bbr_bound_cwnd_for_probe_rtt(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat);
+
+static void bbr_set_cwnd(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                         const ngtcp2_cc_ack *ack);
+
+static void bbr_bound_cwnd_for_model(ngtcp2_bbr2_cc *bbr,
+                                     ngtcp2_conn_stat *cstat);
+
+static void bbr_set_send_quantum(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat);
+
+static int in_congestion_recovery(const ngtcp2_conn_stat *cstat,
+                                  ngtcp2_tstamp sent_time);
+
+static void bbr_handle_recovery(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                const ngtcp2_cc_ack *ack);
+
+static void bbr_on_init(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                        ngtcp2_tstamp initial_ts) {
+  ngtcp2_window_filter_init(&bbr->max_bw_filter, NGTCP2_BBR_MAX_BW_FILTERLEN);
+  ngtcp2_window_filter_init(&bbr->extra_acked_filter,
+                            NGTCP2_BBR_EXTRA_ACKED_FILTERLEN);
+
+  bbr->min_rtt = UINT64_MAX;
+  bbr->min_rtt_stamp = initial_ts;
+  /* remark: Use UINT64_MAX instead of 0 for consistency. */
+  bbr->probe_rtt_done_stamp = UINT64_MAX;
+  bbr->probe_rtt_round_done = 0;
+  bbr->prior_cwnd = 0;
+  bbr->idle_restart = 0;
+  bbr->extra_acked_interval_start = initial_ts;
+  bbr->extra_acked_delivered = 0;
+
+  bbr_reset_congestion_signals(bbr);
+  bbr_reset_lower_bounds(bbr);
+  bbr_init_round_counting(bbr);
+  bbr_init_full_pipe(bbr);
+  bbr_init_pacing_rate(bbr, cstat);
+  bbr_enter_startup(bbr);
+
+  cstat->send_quantum = cstat->max_tx_udp_payload_size * 10;
+
+  /* Missing in documentation */
+  bbr->loss_round_start = 0;
+  bbr->loss_round_delivered = UINT64_MAX;
+
+  bbr->rounds_since_bw_probe = 0;
+
+  bbr->max_bw = 0;
+  bbr->bw = 0;
+
+  bbr->cycle_count = 0;
+
+  bbr->extra_acked = 0;
+
+  bbr->bytes_lost_in_round = 0;
+  bbr->loss_events_in_round = 0;
+
+  bbr->offload_budget = 0;
+
+  bbr->probe_up_cnt = UINT64_MAX;
+  bbr->cycle_stamp = UINT64_MAX;
+  bbr->ack_phase = 0;
+  bbr->bw_probe_wait = 0;
+  bbr->bw_probe_samples = 0;
+  bbr->bw_probe_up_rounds = 0;
+  bbr->bw_probe_up_acks = 0;
+
+  bbr->inflight_hi = UINT64_MAX;
+  bbr->bw_hi = UINT64_MAX;
+
+  bbr->probe_rtt_expired = 0;
+  bbr->probe_rtt_min_delay = UINT64_MAX;
+  bbr->probe_rtt_min_stamp = initial_ts;
+
+  bbr->in_loss_recovery = 0;
+  bbr->packet_conservation = 0;
+
+  bbr->max_inflight = 0;
+
+  bbr->congestion_recovery_start_ts = UINT64_MAX;
+  bbr->congestion_recovery_next_round_delivered = 0;
+
+  bbr->prior_inflight_lo = 0;
+  bbr->prior_inflight_hi = 0;
+  bbr->prior_bw_lo = 0;
+}
+
+static void bbr_reset_congestion_signals(ngtcp2_bbr2_cc *bbr) {
+  bbr->loss_in_round = 0;
+  bbr->bw_latest = 0;
+  bbr->inflight_latest = 0;
+}
+
+static void bbr_reset_lower_bounds(ngtcp2_bbr2_cc *bbr) {
+  bbr->bw_lo = UINT64_MAX;
+  bbr->inflight_lo = UINT64_MAX;
+}
+
+static void bbr_init_round_counting(ngtcp2_bbr2_cc *bbr) {
+  bbr->next_round_delivered = 0;
+  bbr->round_start = 0;
+  bbr->round_count = 0;
+}
+
+static void bbr_init_full_pipe(ngtcp2_bbr2_cc *bbr) {
+  bbr->filled_pipe = 0;
+  bbr->full_bw = 0;
+  bbr->full_bw_count = 0;
+}
+
+static void bbr_check_startup_full_bandwidth(ngtcp2_bbr2_cc *bbr) {
+  if (bbr->filled_pipe || !bbr->round_start || bbr->rst->rs.is_app_limited) {
+    return;
+  }
+
+  if (bbr->max_bw * 100 >= bbr->full_bw * 125) {
+    bbr->full_bw = bbr->max_bw;
+    bbr->full_bw_count = 0;
+  }
+
+  ++bbr->full_bw_count;
+
+  if (bbr->full_bw_count >= 3) {
+    bbr->filled_pipe = 1;
+
+    ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV,
+                    "bbr2 filled pipe, full_bw=%" PRIu64, bbr->full_bw);
+  }
+}
+
+static void bbr_check_startup_high_loss(ngtcp2_bbr2_cc *bbr,
+                                        const ngtcp2_cc_ack *ack) {
+  if (bbr->filled_pipe || !bbr->round_start || bbr->rst->rs.is_app_limited) {
+    return;
+  }
+
+  if (bbr->loss_events_in_round <= 3) {
+    return;
+  }
+
+  /* loss_thresh = 2% */
+  if (bbr->bytes_lost_in_round * 100 <= ack->prior_bytes_in_flight * 2) {
+    return;
+  }
+
+  bbr->filled_pipe = 1;
+}
+
+static void bbr_init_pacing_rate(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat) {
+  double nominal_bandwidth = (double)bbr->initial_cwnd;
+
+  cstat->pacing_rate = NGTCP2_BBR_STARTUP_PACING_GAIN * nominal_bandwidth /
+                       (double)NGTCP2_MILLISECONDS;
+}
+
+static void bbr_set_pacing_rate_with_gain(ngtcp2_bbr2_cc *bbr,
+                                          ngtcp2_conn_stat *cstat,
+                                          double pacing_gain) {
+  double rate = pacing_gain * (double)bbr->bw *
+                (100 - NGTCP2_BBR_PACING_MARGIN_PERCENT) / 100 / NGTCP2_SECONDS;
+
+  if (bbr->filled_pipe || rate > cstat->pacing_rate) {
+    cstat->pacing_rate = rate;
+  }
+}
+
+static void bbr_set_pacing_rate(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat) {
+  bbr_set_pacing_rate_with_gain(bbr, cstat, bbr->pacing_gain);
+}
+
+static void bbr_enter_startup(ngtcp2_bbr2_cc *bbr) {
+  ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV, "bbr2 enter Startup");
+
+  bbr->state = NGTCP2_BBR2_STATE_STARTUP;
+  bbr->pacing_gain = NGTCP2_BBR_STARTUP_PACING_GAIN;
+  bbr->cwnd_gain = NGTCP2_BBR_STARTUP_CWND_GAIN;
+}
+
+static void bbr_check_startup_done(ngtcp2_bbr2_cc *bbr,
+                                   const ngtcp2_cc_ack *ack) {
+  bbr_check_startup_full_bandwidth(bbr);
+  bbr_check_startup_high_loss(bbr, ack);
+
+  if (bbr->state == NGTCP2_BBR2_STATE_STARTUP && bbr->filled_pipe) {
+    bbr_enter_drain(bbr);
+  }
+}
+
+static void bbr_on_transmit(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                            ngtcp2_tstamp ts) {
+  bbr_handle_restart_from_idle(bbr, cstat, ts);
+}
+
+static void bbr_update_on_ack(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                              const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
+  bbr_update_model_and_state(bbr, cstat, ack, ts);
+  bbr_update_control_parameters(bbr, cstat, ack);
+}
+
+static void bbr_update_model_and_state(ngtcp2_bbr2_cc *bbr,
+                                       ngtcp2_conn_stat *cstat,
+                                       const ngtcp2_cc_ack *ack,
+                                       ngtcp2_tstamp ts) {
+  bbr_update_latest_delivery_signals(bbr, cstat);
+  bbr_update_congestion_signals(bbr, cstat, ack);
+  bbr_update_ack_aggregation(bbr, cstat, ack, ts);
+  bbr_check_startup_done(bbr, ack);
+  bbr_check_drain(bbr, cstat, ts);
+  bbr_update_probe_bw_cycle_phase(bbr, cstat, ack, ts);
+  bbr_update_min_rtt(bbr, ack, ts);
+  bbr_check_probe_rtt(bbr, cstat, ts);
+  bbr_advance_latest_delivery_signals(bbr, cstat);
+  bbr_bound_bw_for_model(bbr);
+}
+
+static void bbr_update_control_parameters(ngtcp2_bbr2_cc *bbr,
+                                          ngtcp2_conn_stat *cstat,
+                                          const ngtcp2_cc_ack *ack) {
+  bbr_set_pacing_rate(bbr, cstat);
+  bbr_set_send_quantum(bbr, cstat);
+  bbr_set_cwnd(bbr, cstat, ack);
+}
+
+static void bbr_update_on_loss(ngtcp2_bbr2_cc *cc, ngtcp2_conn_stat *cstat,
+                               const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
+  bbr_handle_lost_packet(cc, cstat, pkt, ts);
+}
+
+static void bbr_update_latest_delivery_signals(ngtcp2_bbr2_cc *bbr,
+                                               ngtcp2_conn_stat *cstat) {
+  bbr->loss_round_start = 0;
+  bbr->bw_latest = ngtcp2_max(bbr->bw_latest, cstat->delivery_rate_sec);
+  bbr->inflight_latest =
+      ngtcp2_max(bbr->inflight_latest, bbr->rst->rs.delivered);
+
+  if (bbr->rst->rs.prior_delivered >= bbr->loss_round_delivered) {
+    bbr->loss_round_delivered = bbr->rst->delivered;
+    bbr->loss_round_start = 1;
+  }
+}
+
+static void bbr_advance_latest_delivery_signals(ngtcp2_bbr2_cc *bbr,
+                                                ngtcp2_conn_stat *cstat) {
+  if (bbr->loss_round_start) {
+    bbr->bw_latest = cstat->delivery_rate_sec;
+    bbr->inflight_latest = bbr->rst->rs.delivered;
+  }
+}
+
+static void bbr_update_congestion_signals(ngtcp2_bbr2_cc *bbr,
+                                          ngtcp2_conn_stat *cstat,
+                                          const ngtcp2_cc_ack *ack) {
+  bbr_update_max_bw(bbr, cstat, ack);
+
+  if (ack->bytes_lost) {
+    bbr->bytes_lost_in_round += ack->bytes_lost;
+    ++bbr->loss_events_in_round;
+
+    if (!bbr->loss_in_round) {
+      bbr->loss_in_round = 1;
+      bbr->loss_round_delivered = bbr->rst->delivered;
+    }
+  }
+
+  if (!bbr->loss_round_start) {
+    return;
+  }
+
+  bbr_adapt_lower_bounds_from_congestion(bbr, cstat);
+
+  bbr->loss_in_round = 0;
+}
+
+static void bbr_adapt_lower_bounds_from_congestion(ngtcp2_bbr2_cc *bbr,
+                                                   ngtcp2_conn_stat *cstat) {
+  if (!bbr->filled_pipe || bbr_is_in_probe_bw_state(bbr)) {
+    return;
+  }
+
+  if (bbr->loss_in_round) {
+    bbr_init_lower_bounds(bbr, cstat);
+    bbr_loss_lower_bounds(bbr);
+  }
+}
+
+static void bbr_init_lower_bounds(ngtcp2_bbr2_cc *bbr,
+                                  ngtcp2_conn_stat *cstat) {
+  if (bbr->bw_lo == UINT64_MAX) {
+    bbr->bw_lo = bbr->max_bw;
+  }
+
+  if (bbr->inflight_lo == UINT64_MAX) {
+    bbr->inflight_lo = cstat->cwnd;
+  }
+}
+
+static void bbr_loss_lower_bounds(ngtcp2_bbr2_cc *bbr) {
+  bbr->bw_lo = ngtcp2_max(bbr->bw_latest, bbr->bw_lo * NGTCP2_BBR_BETA_NUMER /
+                                              NGTCP2_BBR_BETA_DENOM);
+  bbr->inflight_lo = ngtcp2_max(bbr->inflight_latest,
+                                bbr->inflight_lo * NGTCP2_BBR_BETA_NUMER /
+                                    NGTCP2_BBR_BETA_DENOM);
+}
+
+static void bbr_bound_bw_for_model(ngtcp2_bbr2_cc *bbr) {
+  bbr->bw = ngtcp2_min(bbr->max_bw, bbr->bw_lo);
+  bbr->bw = ngtcp2_min(bbr->bw, bbr->bw_hi);
+}
+
+static void bbr_update_max_bw(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                              const ngtcp2_cc_ack *ack) {
+  bbr_update_round(bbr, ack);
+  bbr_handle_recovery(bbr, cstat, ack);
+
+  if (cstat->delivery_rate_sec >= bbr->max_bw || !bbr->rst->rs.is_app_limited) {
+    ngtcp2_window_filter_update(&bbr->max_bw_filter, cstat->delivery_rate_sec,
+                                bbr->cycle_count);
+
+    bbr->max_bw = ngtcp2_window_filter_get_best(&bbr->max_bw_filter);
+  }
+}
+
+static void bbr_update_round(ngtcp2_bbr2_cc *bbr, const ngtcp2_cc_ack *ack) {
+  if (ack->pkt_delivered >= bbr->next_round_delivered) {
+    bbr_start_round(bbr);
+
+    ++bbr->round_count;
+    ++bbr->rounds_since_bw_probe;
+    bbr->round_start = 1;
+
+    bbr->bytes_lost_in_round = 0;
+    bbr->loss_events_in_round = 0;
+
+    bbr->rst->is_cwnd_limited = 0;
+
+    return;
+  }
+
+  bbr->round_start = 0;
+}
+
+static void bbr_start_round(ngtcp2_bbr2_cc *bbr) {
+  bbr->next_round_delivered = bbr->rst->delivered;
+}
+
+static int bbr_is_in_probe_bw_state(ngtcp2_bbr2_cc *bbr) {
+  switch (bbr->state) {
+  case NGTCP2_BBR2_STATE_PROBE_BW_DOWN:
+  case NGTCP2_BBR2_STATE_PROBE_BW_CRUISE:
+  case NGTCP2_BBR2_STATE_PROBE_BW_REFILL:
+  case NGTCP2_BBR2_STATE_PROBE_BW_UP:
+    return 1;
+  default:
+    return 0;
+  }
+}
+
+static void bbr_update_ack_aggregation(ngtcp2_bbr2_cc *bbr,
+                                       ngtcp2_conn_stat *cstat,
+                                       const ngtcp2_cc_ack *ack,
+                                       ngtcp2_tstamp ts) {
+  ngtcp2_duration interval = ts - bbr->extra_acked_interval_start;
+  uint64_t expected_delivered = bbr->bw * interval / NGTCP2_SECONDS;
+  uint64_t extra;
+
+  if (bbr->extra_acked_delivered <= expected_delivered) {
+    bbr->extra_acked_delivered = 0;
+    bbr->extra_acked_interval_start = ts;
+    expected_delivered = 0;
+  }
+
+  bbr->extra_acked_delivered += ack->bytes_delivered;
+  extra = bbr->extra_acked_delivered - expected_delivered;
+  extra = ngtcp2_min(extra, cstat->cwnd);
+
+  ngtcp2_window_filter_update(&bbr->extra_acked_filter, extra,
+                              bbr->round_count);
+
+  bbr->extra_acked = ngtcp2_window_filter_get_best(&bbr->extra_acked_filter);
+}
+
+static void bbr_enter_drain(ngtcp2_bbr2_cc *bbr) {
+  ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV, "bbr2 enter Drain");
+
+  bbr->state = NGTCP2_BBR2_STATE_DRAIN;
+  bbr->pacing_gain = 1. / NGTCP2_BBR_STARTUP_CWND_GAIN;
+  bbr->cwnd_gain = NGTCP2_BBR_STARTUP_CWND_GAIN;
+}
+
+static void bbr_check_drain(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                            ngtcp2_tstamp ts) {
+  if (bbr->state == NGTCP2_BBR2_STATE_DRAIN &&
+      cstat->bytes_in_flight <= bbr_inflight(bbr, cstat, bbr->bw, 1.0)) {
+    bbr_enter_probe_bw(bbr, ts);
+  }
+}
+
+static void bbr_enter_probe_bw(ngtcp2_bbr2_cc *bbr, ngtcp2_tstamp ts) {
+  bbr_start_probe_bw_down(bbr, ts);
+}
+
+static void bbr_start_probe_bw_down(ngtcp2_bbr2_cc *bbr, ngtcp2_tstamp ts) {
+  ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV,
+                  "bbr2 start ProbeBW_DOWN");
+
+  bbr_reset_congestion_signals(bbr);
+
+  bbr->probe_up_cnt = UINT64_MAX;
+
+  bbr_pick_probe_wait(bbr);
+
+  bbr->cycle_stamp = ts;
+  bbr->ack_phase = NGTCP2_BBR2_ACK_PHASE_ACKS_PROBE_STOPPING;
+
+  bbr_start_round(bbr);
+
+  bbr->state = NGTCP2_BBR2_STATE_PROBE_BW_DOWN;
+  bbr->pacing_gain = 0.9;
+  bbr->cwnd_gain = 2;
+}
+
+static void bbr_start_probe_bw_cruise(ngtcp2_bbr2_cc *bbr) {
+  ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV,
+                  "bbr2 start ProbeBW_CRUISE");
+
+  bbr->state = NGTCP2_BBR2_STATE_PROBE_BW_CRUISE;
+  bbr->pacing_gain = 1.0;
+  bbr->cwnd_gain = 2;
+}
+
+static void bbr_start_probe_bw_refill(ngtcp2_bbr2_cc *bbr) {
+  ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV,
+                  "bbr2 start ProbeBW_REFILL");
+
+  bbr_reset_lower_bounds(bbr);
+
+  bbr->bw_probe_up_rounds = 0;
+  bbr->bw_probe_up_acks = 0;
+  bbr->ack_phase = NGTCP2_BBR2_ACK_PHASE_ACKS_REFILLING;
+
+  bbr_start_round(bbr);
+
+  bbr->state = NGTCP2_BBR2_STATE_PROBE_BW_REFILL;
+  bbr->pacing_gain = 1.0;
+  bbr->cwnd_gain = 2;
+}
+
+static void bbr_start_probe_bw_up(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                  ngtcp2_tstamp ts) {
+  ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV, "bbr2 start ProbeBW_UP");
+
+  bbr->ack_phase = NGTCP2_BBR2_ACK_PHASE_ACKS_PROBE_STARTING;
+
+  bbr_start_round(bbr);
+
+  bbr->cycle_stamp = ts;
+  bbr->state = NGTCP2_BBR2_STATE_PROBE_BW_UP;
+  bbr->pacing_gain = 1.25;
+  bbr->cwnd_gain = 2;
+
+  bbr_raise_inflight_hi_slope(bbr, cstat);
+}
+
+static void bbr_update_probe_bw_cycle_phase(ngtcp2_bbr2_cc *bbr,
+                                            ngtcp2_conn_stat *cstat,
+                                            const ngtcp2_cc_ack *ack,
+                                            ngtcp2_tstamp ts) {
+  if (!bbr->filled_pipe) {
+    return;
+  }
+
+  bbr_adapt_upper_bounds(bbr, cstat, ack, ts);
+
+  if (!bbr_is_in_probe_bw_state(bbr)) {
+    return;
+  }
+
+  switch (bbr->state) {
+  case NGTCP2_BBR2_STATE_PROBE_BW_DOWN:
+    if (bbr_check_time_to_probe_bw(bbr, cstat, ts)) {
+      return;
+    }
+
+    if (bbr_check_time_to_cruise(bbr, cstat, ts)) {
+      bbr_start_probe_bw_cruise(bbr);
+    }
+
+    break;
+  case NGTCP2_BBR2_STATE_PROBE_BW_CRUISE:
+    if (bbr_check_time_to_probe_bw(bbr, cstat, ts)) {
+      return;
+    }
+
+    break;
+  case NGTCP2_BBR2_STATE_PROBE_BW_REFILL:
+    if (bbr->round_start) {
+      bbr->bw_probe_samples = 1;
+      bbr_start_probe_bw_up(bbr, cstat, ts);
+    }
+
+    break;
+  case NGTCP2_BBR2_STATE_PROBE_BW_UP:
+    if (bbr_has_elapsed_in_phase(bbr, bbr->min_rtt, ts) &&
+        cstat->bytes_in_flight > bbr_inflight(bbr, cstat, bbr->max_bw, 1.25)) {
+      bbr_start_probe_bw_down(bbr, ts);
+    }
+
+    break;
+  default:
+    break;
+  }
+}
+
+static int bbr_check_time_to_cruise(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_conn_stat *cstat, ngtcp2_tstamp ts) {
+  (void)ts;
+
+  if (cstat->bytes_in_flight > bbr_inflight_with_headroom(bbr, cstat)) {
+    return 0;
+  }
+
+  if (cstat->bytes_in_flight <= bbr_inflight(bbr, cstat, bbr->max_bw, 1.0)) {
+    return 1;
+  }
+
+  return 0;
+}
+
+static int bbr_has_elapsed_in_phase(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_duration interval,
+                                    ngtcp2_tstamp ts) {
+  return ts > bbr->cycle_stamp + interval;
+}
+
+static uint64_t bbr_inflight_with_headroom(ngtcp2_bbr2_cc *bbr,
+                                           ngtcp2_conn_stat *cstat) {
+  uint64_t headroom;
+  uint64_t mpcwnd;
+  if (bbr->inflight_hi == UINT64_MAX) {
+    return UINT64_MAX;
+  }
+
+  headroom = ngtcp2_max(cstat->max_tx_udp_payload_size,
+                        bbr->inflight_hi * NGTCP2_BBR_HEADROOM_NUMER /
+                            NGTCP2_BBR_HEADROOM_DENOM);
+  mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
+
+  if (bbr->inflight_hi > headroom) {
+    return ngtcp2_max(bbr->inflight_hi - headroom, mpcwnd);
+  }
+
+  return mpcwnd;
+}
+
+static void bbr_raise_inflight_hi_slope(ngtcp2_bbr2_cc *bbr,
+                                        ngtcp2_conn_stat *cstat) {
+  uint64_t growth_this_round = cstat->max_tx_udp_payload_size
+                               << bbr->bw_probe_up_rounds;
+
+  bbr->bw_probe_up_rounds = ngtcp2_min(bbr->bw_probe_up_rounds + 1, 30);
+  bbr->probe_up_cnt = ngtcp2_max(cstat->cwnd / growth_this_round, 1) *
+                      cstat->max_tx_udp_payload_size;
+}
+
+static void bbr_probe_inflight_hi_upward(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat,
+                                         const ngtcp2_cc_ack *ack) {
+  uint64_t delta;
+
+  if (!bbr->rst->is_cwnd_limited || cstat->cwnd < bbr->inflight_hi) {
+    return;
+  }
+
+  bbr->bw_probe_up_acks += ack->bytes_delivered;
+
+  if (bbr->bw_probe_up_acks >= bbr->probe_up_cnt) {
+    delta = bbr->bw_probe_up_acks / bbr->probe_up_cnt;
+    bbr->bw_probe_up_acks -= delta * bbr->probe_up_cnt;
+    bbr->inflight_hi += delta * cstat->max_tx_udp_payload_size;
+  }
+
+  if (bbr->round_start) {
+    bbr_raise_inflight_hi_slope(bbr, cstat);
+  }
+}
+
+static void bbr_adapt_upper_bounds(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                   const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
+  if (bbr->ack_phase == NGTCP2_BBR2_ACK_PHASE_ACKS_PROBE_STARTING &&
+      bbr->round_start) {
+    bbr->ack_phase = NGTCP2_BBR2_ACK_PHASE_ACKS_PROBE_FEEDBACK;
+  }
+
+  if (bbr->ack_phase == NGTCP2_BBR2_ACK_PHASE_ACKS_PROBE_STOPPING &&
+      bbr->round_start) {
+    if (bbr_is_in_probe_bw_state(bbr) && !bbr->rst->rs.is_app_limited) {
+      bbr_advance_max_bw_filter(bbr);
+    }
+  }
+
+  if (!bbr_check_inflight_too_high(bbr, cstat, ts)) {
+    /* bbr->bw_hi never be updated */
+    if (bbr->inflight_hi == UINT64_MAX /* || bbr->bw_hi == UINT64_MAX */) {
+      return;
+    }
+
+    if (bbr->rst->rs.tx_in_flight > bbr->inflight_hi) {
+      bbr->inflight_hi = bbr->rst->rs.tx_in_flight;
+    }
+
+    if (cstat->delivery_rate_sec > bbr->bw_hi) {
+      bbr->bw_hi = cstat->delivery_rate_sec;
+    }
+
+    if (bbr->state == NGTCP2_BBR2_STATE_PROBE_BW_UP) {
+      bbr_probe_inflight_hi_upward(bbr, cstat, ack);
+    }
+  }
+}
+
+static int bbr_check_time_to_probe_bw(ngtcp2_bbr2_cc *bbr,
+                                      ngtcp2_conn_stat *cstat,
+                                      ngtcp2_tstamp ts) {
+  if (bbr_has_elapsed_in_phase(bbr, bbr->bw_probe_wait, ts) ||
+      bbr_is_reno_coexistence_probe_time(bbr, cstat)) {
+    bbr_start_probe_bw_refill(bbr);
+
+    return 1;
+  }
+
+  return 0;
+}
+
+static void bbr_pick_probe_wait(ngtcp2_bbr2_cc *bbr) {
+  uint8_t rand;
+
+  bbr->rand(&rand, 1, &bbr->rand_ctx);
+
+  bbr->rounds_since_bw_probe = (uint64_t)(rand * 2 / 256);
+
+  bbr->rand(&rand, 1, &bbr->rand_ctx);
+
+  bbr->bw_probe_wait = 2 * NGTCP2_SECONDS +
+                       (ngtcp2_tstamp)((double)rand / 255. * NGTCP2_SECONDS);
+}
+
+static int bbr_is_reno_coexistence_probe_time(ngtcp2_bbr2_cc *bbr,
+                                              ngtcp2_conn_stat *cstat) {
+  uint64_t reno_rounds =
+      bbr_target_inflight(bbr, cstat) / cstat->max_tx_udp_payload_size;
+
+  return bbr->rounds_since_bw_probe >= ngtcp2_min(reno_rounds, 63);
+}
+
+static uint64_t bbr_target_inflight(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_conn_stat *cstat) {
+  uint64_t bdp = bbr_inflight(bbr, cstat, bbr->bw, 1.0);
+
+  return ngtcp2_min(bdp, cstat->cwnd);
+}
+
+static int bbr_check_inflight_too_high(ngtcp2_bbr2_cc *bbr,
+                                       ngtcp2_conn_stat *cstat,
+                                       ngtcp2_tstamp ts) {
+  if (is_inflight_too_high(&bbr->rst->rs)) {
+    if (bbr->bw_probe_samples) {
+      bbr_handle_inflight_too_high(bbr, cstat, &bbr->rst->rs, ts);
+    }
+
+    return 1;
+  }
+
+  return 0;
+}
+
+static int is_inflight_too_high(const ngtcp2_rs *rs) {
+  return rs->lost * NGTCP2_BBR_LOSS_THRESH_DENOM >
+         rs->tx_in_flight * NGTCP2_BBR_LOSS_THRESH_NUMER;
+}
+
+static void bbr_handle_inflight_too_high(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat,
+                                         const ngtcp2_rs *rs,
+                                         ngtcp2_tstamp ts) {
+  bbr->bw_probe_samples = 0;
+
+  if (!rs->is_app_limited) {
+    bbr->prior_inflight_hi = bbr->inflight_hi;
+
+    bbr->inflight_hi = ngtcp2_max(
+        rs->tx_in_flight, bbr_target_inflight(bbr, cstat) *
+                              NGTCP2_BBR_BETA_NUMER / NGTCP2_BBR_BETA_DENOM);
+  }
+
+  if (bbr->state == NGTCP2_BBR2_STATE_PROBE_BW_UP) {
+    bbr_start_probe_bw_down(bbr, ts);
+  }
+}
+
+static void bbr_handle_lost_packet(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                   const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
+  ngtcp2_rs rs = {0};
+
+  if (!bbr->bw_probe_samples) {
+    return;
+  }
+
+  rs.tx_in_flight = pkt->tx_in_flight;
+  /* bbr->rst->lost is not incremented for pkt yet */
+  rs.lost = bbr->rst->lost + pkt->pktlen - pkt->lost;
+  rs.is_app_limited = pkt->is_app_limited;
+
+  if (is_inflight_too_high(&rs)) {
+    rs.tx_in_flight = bbr_inflight_hi_from_lost_packet(bbr, &rs, pkt);
+
+    bbr_handle_inflight_too_high(bbr, cstat, &rs, ts);
+  }
+}
+
+static uint64_t bbr_inflight_hi_from_lost_packet(ngtcp2_bbr2_cc *bbr,
+                                                 const ngtcp2_rs *rs,
+                                                 const ngtcp2_cc_pkt *pkt) {
+  uint64_t inflight_prev, lost_prev, lost_prefix;
+  (void)bbr;
+
+  assert(rs->tx_in_flight >= pkt->pktlen);
+
+  inflight_prev = rs->tx_in_flight - pkt->pktlen;
+
+  assert(rs->lost >= pkt->pktlen);
+
+  lost_prev = rs->lost - pkt->pktlen;
+
+  if (inflight_prev * NGTCP2_BBR_LOSS_THRESH_NUMER <
+      lost_prev * NGTCP2_BBR_LOSS_THRESH_DENOM) {
+    return inflight_prev;
+  }
+
+  lost_prefix = (inflight_prev * NGTCP2_BBR_LOSS_THRESH_NUMER -
+                 lost_prev * NGTCP2_BBR_LOSS_THRESH_DENOM) /
+                (NGTCP2_BBR_LOSS_THRESH_DENOM - NGTCP2_BBR_LOSS_THRESH_NUMER);
+
+  return inflight_prev + lost_prefix;
+}
+
+static void bbr_update_min_rtt(ngtcp2_bbr2_cc *bbr, const ngtcp2_cc_ack *ack,
+                               ngtcp2_tstamp ts) {
+  int min_rtt_expired;
+
+  bbr->probe_rtt_expired =
+      ts > bbr->probe_rtt_min_stamp + NGTCP2_BBR_PROBE_RTT_INTERVAL;
+
+  if (ack->rtt != UINT64_MAX &&
+      (ack->rtt < bbr->probe_rtt_min_delay || bbr->probe_rtt_expired)) {
+    bbr->probe_rtt_min_delay = ack->rtt;
+    bbr->probe_rtt_min_stamp = ts;
+  }
+
+  min_rtt_expired = ts > bbr->min_rtt_stamp + NGTCP2_BBR_MIN_RTT_FILTERLEN;
+
+  if (bbr->probe_rtt_min_delay < bbr->min_rtt || min_rtt_expired) {
+    bbr->min_rtt = bbr->probe_rtt_min_delay;
+    bbr->min_rtt_stamp = bbr->probe_rtt_min_stamp;
+
+    ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV,
+                    "bbr2 update min_rtt=%" PRIu64, bbr->min_rtt);
+  }
+}
+
+static void bbr_check_probe_rtt(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                ngtcp2_tstamp ts) {
+  if (bbr->state != NGTCP2_BBR2_STATE_PROBE_RTT && bbr->probe_rtt_expired &&
+      !bbr->idle_restart) {
+    bbr_enter_probe_rtt(bbr);
+    bbr_save_cwnd(bbr, cstat);
+
+    bbr->probe_rtt_done_stamp = UINT64_MAX;
+    bbr->ack_phase = NGTCP2_BBR2_ACK_PHASE_ACKS_PROBE_STOPPING;
+
+    bbr_start_round(bbr);
+  }
+
+  if (bbr->state == NGTCP2_BBR2_STATE_PROBE_RTT) {
+    bbr_handle_probe_rtt(bbr, cstat, ts);
+  }
+
+  if (bbr->rst->rs.delivered) {
+    bbr->idle_restart = 0;
+  }
+}
+
+static void bbr_enter_probe_rtt(ngtcp2_bbr2_cc *bbr) {
+  ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV, "bbr2 enter ProbeRTT");
+
+  bbr->state = NGTCP2_BBR2_STATE_PROBE_RTT;
+  bbr->pacing_gain = 1;
+  bbr->cwnd_gain = NGTCP2_BBR_PROBE_RTT_CWND_GAIN;
+}
+
+static void bbr_handle_probe_rtt(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                 ngtcp2_tstamp ts) {
+  bbr_mark_connection_app_limited(bbr, cstat);
+
+  if (bbr->probe_rtt_done_stamp == UINT64_MAX &&
+      cstat->bytes_in_flight <= bbr_probe_rtt_cwnd(bbr, cstat)) {
+    bbr->probe_rtt_done_stamp = ts + NGTCP2_BBR_PROBE_RTT_DURATION;
+    bbr->probe_rtt_round_done = 0;
+
+    bbr_start_round(bbr);
+
+    return;
+  }
+
+  if (bbr->probe_rtt_done_stamp != UINT64_MAX) {
+    if (bbr->round_start) {
+      bbr->probe_rtt_round_done = 1;
+    }
+
+    if (bbr->probe_rtt_round_done) {
+      bbr_check_probe_rtt_done(bbr, cstat, ts);
+    }
+  }
+}
+
+static void bbr_check_probe_rtt_done(ngtcp2_bbr2_cc *bbr,
+                                     ngtcp2_conn_stat *cstat,
+                                     ngtcp2_tstamp ts) {
+  if (bbr->probe_rtt_done_stamp != UINT64_MAX &&
+      ts > bbr->probe_rtt_done_stamp) {
+    bbr->probe_rtt_min_stamp = ts;
+    bbr_restore_cwnd(bbr, cstat);
+    bbr_exit_probe_rtt(bbr, ts);
+  }
+}
+
+static void bbr_mark_connection_app_limited(ngtcp2_bbr2_cc *bbr,
+                                            ngtcp2_conn_stat *cstat) {
+  uint64_t app_limited = bbr->rst->delivered + cstat->bytes_in_flight;
+
+  if (app_limited) {
+    bbr->rst->app_limited = app_limited;
+  } else {
+    bbr->rst->app_limited = cstat->max_tx_udp_payload_size;
+  }
+}
+
+static void bbr_exit_probe_rtt(ngtcp2_bbr2_cc *bbr, ngtcp2_tstamp ts) {
+  bbr_reset_lower_bounds(bbr);
+
+  if (bbr->filled_pipe) {
+    bbr_start_probe_bw_down(bbr, ts);
+    bbr_start_probe_bw_cruise(bbr);
+  } else {
+    bbr_enter_startup(bbr);
+  }
+}
+
+static void bbr_handle_restart_from_idle(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat,
+                                         ngtcp2_tstamp ts) {
+  if (cstat->bytes_in_flight == 0 && bbr->rst->app_limited) {
+    ngtcp2_log_info(bbr->ccb.log, NGTCP2_LOG_EVENT_RCV,
+                    "bbr2 restart from idle");
+
+    bbr->idle_restart = 1;
+    bbr->extra_acked_interval_start = ts;
+
+    if (bbr_is_in_probe_bw_state(bbr)) {
+      bbr_set_pacing_rate_with_gain(bbr, cstat, 1);
+    } else if (bbr->state == NGTCP2_BBR2_STATE_PROBE_RTT) {
+      bbr_check_probe_rtt_done(bbr, cstat, ts);
+    }
+  }
+}
+
+static uint64_t bbr_bdp_multiple(ngtcp2_bbr2_cc *bbr, uint64_t bw,
+                                 double gain) {
+  uint64_t bdp;
+
+  if (bbr->min_rtt == UINT64_MAX) {
+    return bbr->initial_cwnd;
+  }
+
+  bdp = bw * bbr->min_rtt / NGTCP2_SECONDS;
+
+  return (uint64_t)(gain * (double)bdp);
+}
+
+static uint64_t min_pipe_cwnd(size_t max_udp_payload_size) {
+  return max_udp_payload_size * 4;
+}
+
+static uint64_t bbr_quantization_budget(ngtcp2_bbr2_cc *bbr,
+                                        ngtcp2_conn_stat *cstat,
+                                        uint64_t inflight) {
+  bbr_update_offload_budget(bbr, cstat);
+
+  inflight = ngtcp2_max(inflight, bbr->offload_budget);
+  inflight =
+      ngtcp2_max(inflight, min_pipe_cwnd(cstat->max_tx_udp_payload_size));
+
+  if (bbr->state == NGTCP2_BBR2_STATE_PROBE_BW_UP) {
+    inflight += 2 * cstat->max_tx_udp_payload_size;
+  }
+
+  return inflight;
+}
+
+static uint64_t bbr_inflight(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                             uint64_t bw, double gain) {
+  uint64_t inflight = bbr_bdp_multiple(bbr, bw, gain);
+
+  return bbr_quantization_budget(bbr, cstat, inflight);
+}
+
+static void bbr_update_max_inflight(ngtcp2_bbr2_cc *bbr,
+                                    ngtcp2_conn_stat *cstat) {
+  uint64_t inflight;
+
+  /* Not documented */
+  /* bbr_update_aggregation_budget(bbr); */
+
+  inflight = bbr_bdp_multiple(bbr, bbr->bw, bbr->cwnd_gain) + bbr->extra_acked;
+  bbr->max_inflight = bbr_quantization_budget(bbr, cstat, inflight);
+}
+
+static void bbr_update_offload_budget(ngtcp2_bbr2_cc *bbr,
+                                      ngtcp2_conn_stat *cstat) {
+  bbr->offload_budget = 3 * cstat->send_quantum;
+}
+
+static void bbr_advance_max_bw_filter(ngtcp2_bbr2_cc *bbr) {
+  ++bbr->cycle_count;
+}
+
+static void bbr_modulate_cwnd_for_recovery(ngtcp2_bbr2_cc *bbr,
+                                           ngtcp2_conn_stat *cstat,
+                                           const ngtcp2_cc_ack *ack) {
+  if (ack->bytes_lost > 0) {
+    if (cstat->cwnd > ack->bytes_lost) {
+      cstat->cwnd -= ack->bytes_lost;
+      cstat->cwnd = ngtcp2_max(cstat->cwnd, 2 * cstat->max_tx_udp_payload_size);
+    } else {
+      cstat->cwnd = 2 * cstat->max_tx_udp_payload_size;
+    }
+  }
+
+  if (bbr->packet_conservation) {
+    cstat->cwnd =
+        ngtcp2_max(cstat->cwnd, cstat->bytes_in_flight + ack->bytes_delivered);
+  }
+}
+
+static void bbr_save_cwnd(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat) {
+  if (!bbr->in_loss_recovery && bbr->state != NGTCP2_BBR2_STATE_PROBE_RTT) {
+    bbr->prior_cwnd = cstat->cwnd;
+    return;
+  }
+
+  bbr->prior_cwnd = ngtcp2_max(bbr->prior_cwnd, cstat->cwnd);
+}
+
+static void bbr_restore_cwnd(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat) {
+  cstat->cwnd = ngtcp2_max(cstat->cwnd, bbr->prior_cwnd);
+}
+
+static uint64_t bbr_probe_rtt_cwnd(ngtcp2_bbr2_cc *bbr,
+                                   ngtcp2_conn_stat *cstat) {
+  uint64_t probe_rtt_cwnd =
+      bbr_bdp_multiple(bbr, bbr->bw, NGTCP2_BBR_PROBE_RTT_CWND_GAIN);
+  uint64_t mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
+
+  return ngtcp2_max(probe_rtt_cwnd, mpcwnd);
+}
+
+static void bbr_bound_cwnd_for_probe_rtt(ngtcp2_bbr2_cc *bbr,
+                                         ngtcp2_conn_stat *cstat) {
+  uint64_t probe_rtt_cwnd;
+
+  if (bbr->state == NGTCP2_BBR2_STATE_PROBE_RTT) {
+    probe_rtt_cwnd = bbr_probe_rtt_cwnd(bbr, cstat);
+
+    cstat->cwnd = ngtcp2_min(cstat->cwnd, probe_rtt_cwnd);
+  }
+}
+
+static void bbr_set_cwnd(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                         const ngtcp2_cc_ack *ack) {
+  uint64_t mpcwnd;
+
+  bbr_update_max_inflight(bbr, cstat);
+  bbr_modulate_cwnd_for_recovery(bbr, cstat, ack);
+
+  if (!bbr->packet_conservation) {
+    if (bbr->filled_pipe) {
+      cstat->cwnd += ack->bytes_delivered;
+      cstat->cwnd = ngtcp2_min(cstat->cwnd, bbr->max_inflight);
+    } else if (cstat->cwnd < bbr->max_inflight ||
+               bbr->rst->delivered < bbr->initial_cwnd) {
+      cstat->cwnd += ack->bytes_delivered;
+    }
+
+    mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
+    cstat->cwnd = ngtcp2_max(cstat->cwnd, mpcwnd);
+  }
+
+  bbr_bound_cwnd_for_probe_rtt(bbr, cstat);
+  bbr_bound_cwnd_for_model(bbr, cstat);
+}
+
+static void bbr_bound_cwnd_for_model(ngtcp2_bbr2_cc *bbr,
+                                     ngtcp2_conn_stat *cstat) {
+  uint64_t cap = UINT64_MAX;
+  uint64_t mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
+
+  if (bbr_is_in_probe_bw_state(bbr) &&
+      bbr->state != NGTCP2_BBR2_STATE_PROBE_BW_CRUISE) {
+    cap = bbr->inflight_hi;
+  } else if (bbr->state == NGTCP2_BBR2_STATE_PROBE_RTT ||
+             bbr->state == NGTCP2_BBR2_STATE_PROBE_BW_CRUISE) {
+    cap = bbr_inflight_with_headroom(bbr, cstat);
+  }
+
+  cap = ngtcp2_min(cap, bbr->inflight_lo);
+  cap = ngtcp2_max(cap, mpcwnd);
+
+  cstat->cwnd = ngtcp2_min(cstat->cwnd, cap);
+}
+
+static void bbr_set_send_quantum(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat) {
+  size_t send_quantum =
+      (size_t)(cstat->pacing_rate * (double)(bbr->min_rtt == UINT64_MAX
+                                                 ? NGTCP2_MILLISECONDS
+                                                 : bbr->min_rtt));
+  (void)bbr;
+
+  cstat->send_quantum = ngtcp2_min(send_quantum, 64 * 1024);
+  cstat->send_quantum =
+      ngtcp2_max(cstat->send_quantum, cstat->max_tx_udp_payload_size * 10);
+}
+
+static int in_congestion_recovery(const ngtcp2_conn_stat *cstat,
+                                  ngtcp2_tstamp sent_time) {
+  return cstat->congestion_recovery_start_ts != UINT64_MAX &&
+         sent_time <= cstat->congestion_recovery_start_ts;
+}
+
+static void bbr_handle_recovery(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                                const ngtcp2_cc_ack *ack) {
+  if (bbr->in_loss_recovery) {
+    if (ack->pkt_delivered >= bbr->congestion_recovery_next_round_delivered) {
+      bbr->packet_conservation = 0;
+    }
+
+    if (!in_congestion_recovery(cstat, ack->largest_acked_sent_ts)) {
+      bbr->in_loss_recovery = 0;
+      bbr->packet_conservation = 0;
+      bbr_restore_cwnd(bbr, cstat);
+    }
+
+    return;
+  }
+
+  if (bbr->congestion_recovery_start_ts != UINT64_MAX) {
+    bbr->in_loss_recovery = 1;
+    bbr_save_cwnd(bbr, cstat);
+    cstat->cwnd =
+        cstat->bytes_in_flight +
+        ngtcp2_max(ack->bytes_delivered, cstat->max_tx_udp_payload_size);
+
+    cstat->congestion_recovery_start_ts = bbr->congestion_recovery_start_ts;
+    bbr->congestion_recovery_start_ts = UINT64_MAX;
+    bbr->packet_conservation = 1;
+    bbr->congestion_recovery_next_round_delivered = bbr->rst->delivered;
+    bbr->prior_inflight_lo = bbr->inflight_lo;
+    bbr->prior_bw_lo = bbr->bw_lo;
+  }
+}
+
+static void bbr2_cc_init(ngtcp2_bbr2_cc *bbr, ngtcp2_conn_stat *cstat,
+                         ngtcp2_rst *rst, ngtcp2_tstamp initial_ts,
+                         ngtcp2_rand rand, const ngtcp2_rand_ctx *rand_ctx,
+                         ngtcp2_log *log) {
+  bbr->ccb.log = log;
+  bbr->rst = rst;
+  bbr->rand = rand;
+  bbr->rand_ctx = *rand_ctx;
+  bbr->initial_cwnd = cstat->cwnd;
+
+  bbr_on_init(bbr, cstat, initial_ts);
+}
+
+static void bbr2_cc_free(ngtcp2_bbr2_cc *bbr) { (void)bbr; }
+
+static void bbr2_cc_on_pkt_acked(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                                 const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
+  (void)ccx;
+  (void)cstat;
+  (void)pkt;
+  (void)ts;
+}
+
+static void bbr2_cc_on_pkt_lost(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                                const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr2_cc, ccb);
+
+  bbr_update_on_loss(bbr, cstat, pkt, ts);
+}
+
+static void bbr2_cc_congestion_event(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                                     ngtcp2_tstamp sent_ts, ngtcp2_tstamp ts) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr2_cc, ccb);
+
+  if (!bbr->filled_pipe || bbr->in_loss_recovery ||
+      bbr->congestion_recovery_start_ts != UINT64_MAX ||
+      in_congestion_recovery(cstat, sent_ts)) {
+    return;
+  }
+
+  bbr->congestion_recovery_start_ts = ts;
+}
+
+static void bbr2_cc_on_spurious_congestion(ngtcp2_cc *ccx,
+                                           ngtcp2_conn_stat *cstat,
+                                           ngtcp2_tstamp ts) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr2_cc, ccb);
+  (void)ts;
+
+  bbr->congestion_recovery_start_ts = UINT64_MAX;
+  cstat->congestion_recovery_start_ts = UINT64_MAX;
+
+  if (bbr->in_loss_recovery) {
+    bbr->in_loss_recovery = 0;
+    bbr->packet_conservation = 0;
+    bbr_restore_cwnd(bbr, cstat);
+    bbr->full_bw_count = 0;
+    bbr->loss_in_round = 0;
+    bbr->inflight_lo = ngtcp2_max(bbr->inflight_lo, bbr->prior_inflight_lo);
+    bbr->inflight_hi = ngtcp2_max(bbr->inflight_hi, bbr->prior_inflight_hi);
+    bbr->bw_lo = ngtcp2_max(bbr->bw_lo, bbr->prior_bw_lo);
+  }
+}
+
+static void bbr2_cc_on_persistent_congestion(ngtcp2_cc *ccx,
+                                             ngtcp2_conn_stat *cstat,
+                                             ngtcp2_tstamp ts) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr2_cc, ccb);
+  (void)ts;
+
+  cstat->congestion_recovery_start_ts = UINT64_MAX;
+  bbr->congestion_recovery_start_ts = UINT64_MAX;
+  bbr->in_loss_recovery = 0;
+  bbr->packet_conservation = 0;
+
+  bbr_save_cwnd(bbr, cstat);
+  cstat->cwnd = cstat->bytes_in_flight + cstat->max_tx_udp_payload_size;
+  cstat->cwnd =
+      ngtcp2_max(cstat->cwnd, min_pipe_cwnd(cstat->max_tx_udp_payload_size));
+}
+
+static void bbr2_cc_on_ack_recv(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                                const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr2_cc, ccb);
+
+  bbr_update_on_ack(bbr, cstat, ack, ts);
+}
+
+static void bbr2_cc_on_pkt_sent(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                                const ngtcp2_cc_pkt *pkt) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr2_cc, ccb);
+
+  bbr_on_transmit(bbr, cstat, pkt->sent_ts);
+}
+
+static void bbr2_cc_new_rtt_sample(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                                   ngtcp2_tstamp ts) {
+  (void)ccx;
+  (void)cstat;
+  (void)ts;
+}
+
+static void bbr2_cc_reset(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                          ngtcp2_tstamp ts) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr2_cc, ccb);
+
+  bbr_on_init(bbr, cstat, ts);
+}
+
+static void bbr2_cc_event(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
+                          ngtcp2_cc_event_type event, ngtcp2_tstamp ts) {
+  (void)ccx;
+  (void)cstat;
+  (void)event;
+  (void)ts;
+}
+
+int ngtcp2_cc_bbr2_cc_init(ngtcp2_cc *cc, ngtcp2_log *log,
+                           ngtcp2_conn_stat *cstat, ngtcp2_rst *rst,
+                           ngtcp2_tstamp initial_ts, ngtcp2_rand rand,
+                           const ngtcp2_rand_ctx *rand_ctx,
+                           const ngtcp2_mem *mem) {
+  ngtcp2_bbr2_cc *bbr;
+
+  bbr = ngtcp2_mem_calloc(mem, 1, sizeof(ngtcp2_bbr2_cc));
+  if (bbr == NULL) {
+    return NGTCP2_ERR_NOMEM;
+  }
+
+  bbr2_cc_init(bbr, cstat, rst, initial_ts, rand, rand_ctx, log);
+
+  cc->ccb = &bbr->ccb;
+  cc->on_pkt_acked = bbr2_cc_on_pkt_acked;
+  cc->on_pkt_lost = bbr2_cc_on_pkt_lost;
+  cc->congestion_event = bbr2_cc_congestion_event;
+  cc->on_spurious_congestion = bbr2_cc_on_spurious_congestion;
+  cc->on_persistent_congestion = bbr2_cc_on_persistent_congestion;
+  cc->on_ack_recv = bbr2_cc_on_ack_recv;
+  cc->on_pkt_sent = bbr2_cc_on_pkt_sent;
+  cc->new_rtt_sample = bbr2_cc_new_rtt_sample;
+  cc->reset = bbr2_cc_reset;
+  cc->event = bbr2_cc_event;
+
+  return 0;
+}
+
+void ngtcp2_cc_bbr2_cc_free(ngtcp2_cc *cc, const ngtcp2_mem *mem) {
+  ngtcp2_bbr2_cc *bbr = ngtcp2_struct_of(cc->ccb, ngtcp2_bbr2_cc, ccb);
+
+  bbr2_cc_free(bbr);
+  ngtcp2_mem_free(mem, bbr);
+}