| // Copyright (C) 2019, Cloudflare, Inc. |
| // All rights reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright notice, |
| // this list of conditions and the following disclaimer. |
| // |
| // * Redistributions in binary form must reproduce the above copyright |
| // notice, this list of conditions and the following disclaimer in the |
| // documentation and/or other materials provided with the distribution. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS |
| // IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, |
| // THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| // PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR |
| // CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, |
| // EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, |
| // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
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| // NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS |
| // SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| //! CUBIC Congestion Control |
| //! |
| //! This implementation is based on the following draft: |
| //! <https://tools.ietf.org/html/draft-eggert-tcpm-rfc8312bis-02> |
| //! |
| //! Note that Slow Start can use HyStart++ when enabled. |
| |
| use std::cmp; |
| |
| use std::time::Duration; |
| use std::time::Instant; |
| |
| use crate::packet; |
| use crate::recovery; |
| use crate::recovery::reno; |
| |
| use crate::recovery::Acked; |
| use crate::recovery::CongestionControlOps; |
| use crate::recovery::Recovery; |
| |
| pub static CUBIC: CongestionControlOps = CongestionControlOps { |
| on_packet_sent, |
| on_packet_acked, |
| congestion_event, |
| collapse_cwnd, |
| }; |
| |
| /// CUBIC Constants. |
| /// |
| /// These are recommended value in RFC8312. |
| const BETA_CUBIC: f64 = 0.7; |
| |
| const C: f64 = 0.4; |
| |
| /// Default value of alpha_aimd in the beginning of congestion avoidance. |
| const ALPHA_AIMD: f64 = 3.0 * (1.0 - BETA_CUBIC) / (1.0 + BETA_CUBIC); |
| |
| /// CUBIC State Variables. |
| /// |
| /// We need to keep those variables across the connection. |
| /// k, w_max, w_last_max is described in the RFC. |
| #[derive(Debug, Default)] |
| pub struct State { |
| k: f64, |
| |
| w_max: f64, |
| |
| w_last_max: f64, |
| |
| w_est: f64, |
| |
| alpha_aimd: f64, |
| |
| // Used in CUBIC fix (see on_packet_sent()) |
| last_sent_time: Option<Instant>, |
| |
| // Store cwnd increment during congestion avoidance. |
| cwnd_inc: usize, |
| |
| // Reno cwnd |
| reno_cwnd: usize, |
| } |
| |
| /// CUBIC Functions. |
| /// |
| /// Note that these calculations are based on a count of cwnd as bytes, |
| /// not packets. |
| /// Unit of t (duration) and RTT are based on seconds (f64). |
| impl State { |
| // K = cubic_root (w_max * cwnd) / C) (Eq. 2) |
| fn cubic_k(&self, cwnd: usize, max_datagram_size: usize) -> f64 { |
| let w_max = self.w_max / max_datagram_size as f64; |
| let cwnd = cwnd as f64 / max_datagram_size as f64; |
| |
| libm::cbrt((w_max - cwnd) / C) |
| } |
| |
| // W_cubic(t) = C * (t - K)^3 - w_max (Eq. 1) |
| fn w_cubic(&self, t: Duration, max_datagram_size: usize) -> f64 { |
| let w_max = self.w_max / max_datagram_size as f64; |
| |
| (C * (t.as_secs_f64() - self.k).powi(3) + w_max) * |
| max_datagram_size as f64 |
| } |
| |
| // W_est = W_est + alpha_aimd * (segments_acked / cwnd) (Eq. 4) |
| fn w_est_inc( |
| &self, acked: usize, cwnd: usize, max_datagram_size: usize, |
| ) -> f64 { |
| self.alpha_aimd * (acked as f64 / cwnd as f64) * max_datagram_size as f64 |
| } |
| } |
| |
| fn collapse_cwnd(r: &mut Recovery) { |
| let cubic = &mut r.cubic_state; |
| |
| r.congestion_recovery_start_time = None; |
| |
| cubic.w_last_max = r.congestion_window as f64; |
| cubic.w_max = cubic.w_last_max; |
| |
| // 4.7 Timeout - reduce ssthresh based on BETA_CUBIC |
| r.ssthresh = (r.congestion_window as f64 * BETA_CUBIC) as usize; |
| r.ssthresh = cmp::max( |
| r.ssthresh, |
| r.max_datagram_size * recovery::MINIMUM_WINDOW_PACKETS, |
| ); |
| |
| cubic.cwnd_inc = 0; |
| |
| reno::collapse_cwnd(r); |
| } |
| |
| fn on_packet_sent(r: &mut Recovery, sent_bytes: usize, now: Instant) { |
| // See https://github.com/torvalds/linux/commit/30927520dbae297182990bb21d08762bcc35ce1d |
| // First transmit when no packets in flight |
| let cubic = &mut r.cubic_state; |
| |
| if let Some(last_sent_time) = cubic.last_sent_time { |
| if r.bytes_in_flight == 0 { |
| let delta = now - last_sent_time; |
| |
| // We were application limited (idle) for a while. |
| // Shift epoch start to keep cwnd growth to cubic curve. |
| if let Some(recovery_start_time) = r.congestion_recovery_start_time { |
| if delta.as_nanos() > 0 { |
| r.congestion_recovery_start_time = |
| Some(recovery_start_time + delta); |
| } |
| } |
| } |
| } |
| |
| cubic.last_sent_time = Some(now); |
| |
| reno::on_packet_sent(r, sent_bytes, now); |
| } |
| |
| fn on_packet_acked( |
| r: &mut Recovery, packet: &Acked, epoch: packet::Epoch, now: Instant, |
| ) { |
| let in_congestion_recovery = r.in_congestion_recovery(packet.time_sent); |
| |
| r.bytes_in_flight = r.bytes_in_flight.saturating_sub(packet.size); |
| |
| if in_congestion_recovery { |
| return; |
| } |
| |
| if r.app_limited { |
| return; |
| } |
| |
| if r.congestion_window < r.ssthresh { |
| // Slow start. |
| let cwnd_inc = cmp::min( |
| packet.size, |
| r.max_datagram_size * recovery::ABC_L - |
| cmp::min( |
| r.bytes_acked_sl, |
| r.max_datagram_size * recovery::ABC_L, |
| ), |
| ); |
| |
| // In Slow slart, bytes_acked_sl is used for counting |
| // acknowledged bytes. |
| r.bytes_acked_sl += packet.size; |
| |
| r.congestion_window += cwnd_inc; |
| |
| if r.hystart.enabled() && |
| epoch == packet::EPOCH_APPLICATION && |
| r.hystart.try_enter_lss( |
| packet, |
| r.latest_rtt, |
| r.congestion_window, |
| now, |
| r.max_datagram_size, |
| ) |
| { |
| r.ssthresh = r.congestion_window; |
| } |
| } else { |
| // Congestion avoidance. |
| let ca_start_time; |
| |
| // In LSS, use lss_start_time instead of congestion_recovery_start_time. |
| if r.hystart.in_lss(epoch) { |
| ca_start_time = r.hystart.lss_start_time().unwrap(); |
| |
| // Reset w_max and k when LSS started. |
| if r.cubic_state.w_max == 0.0 { |
| r.cubic_state.w_max = r.congestion_window as f64; |
| r.cubic_state.k = 0.0; |
| |
| r.cubic_state.w_est = r.congestion_window as f64; |
| r.cubic_state.alpha_aimd = ALPHA_AIMD; |
| |
| r.cubic_state.reno_cwnd = r.congestion_window; |
| } |
| } else { |
| match r.congestion_recovery_start_time { |
| Some(t) => ca_start_time = t, |
| None => { |
| // When we come here without congestion_event() triggered, |
| // initialize congestion_recovery_start_time, w_max and k. |
| ca_start_time = now; |
| r.congestion_recovery_start_time = Some(now); |
| |
| r.cubic_state.w_max = r.congestion_window as f64; |
| r.cubic_state.k = 0.0; |
| |
| r.cubic_state.w_est = r.congestion_window as f64; |
| r.cubic_state.alpha_aimd = ALPHA_AIMD; |
| |
| r.cubic_state.reno_cwnd = r.congestion_window; |
| }, |
| } |
| } |
| |
| let t = now - ca_start_time; |
| |
| // target = w_cubic(t + rtt) |
| let target = r.cubic_state.w_cubic(t + r.min_rtt, r.max_datagram_size); |
| |
| // Clipping target to [cwnd, 1.5 x cwnd] |
| let target = f64::max(target, r.congestion_window as f64); |
| let target = f64::min(target, r.congestion_window as f64 * 1.5); |
| |
| // Update w_est. |
| let w_est_inc = r.cubic_state.w_est_inc( |
| packet.size, |
| r.congestion_window, |
| r.max_datagram_size, |
| ); |
| r.cubic_state.w_est += w_est_inc; |
| |
| if r.cubic_state.w_est >= r.cubic_state.w_max { |
| r.cubic_state.alpha_aimd = 1.0; |
| } |
| |
| // Reno in parallel. |
| r.bytes_acked_ca += packet.size; |
| |
| if r.bytes_acked_ca >= r.congestion_window { |
| r.bytes_acked_ca -= r.congestion_window; |
| r.cubic_state.reno_cwnd += r.max_datagram_size; |
| } |
| |
| let mut cubic_cwnd = r.congestion_window; |
| |
| if r.cubic_state.w_cubic(t, r.max_datagram_size) < r.cubic_state.w_est { |
| // AIMD friendly region (W_cubic(t) < W_est) |
| cubic_cwnd = cmp::max(cubic_cwnd, r.cubic_state.w_est as usize); |
| |
| } else { |
| // Concave region or convex region use same increment. |
| let cubic_inc = |
| r.max_datagram_size * (target as usize - cubic_cwnd) / cubic_cwnd; |
| |
| cubic_cwnd += cubic_inc; |
| } |
| |
| // When in Limited Slow Start, take the max of CA cwnd and |
| // LSS cwnd. |
| if r.hystart.in_lss(epoch) { |
| let lss_cwnd = r.hystart.lss_cwnd( |
| packet.size, |
| r.bytes_acked_sl, |
| r.congestion_window, |
| r.ssthresh, |
| r.max_datagram_size, |
| ); |
| |
| r.bytes_acked_sl += packet.size; |
| |
| cubic_cwnd = cmp::max(cubic_cwnd, lss_cwnd); |
| } |
| |
| // Update the increment and increase cwnd by MSS. |
| r.cubic_state.cwnd_inc += cubic_cwnd - r.congestion_window; |
| |
| // cwnd_inc can be more than 1 MSS in the late stage of max probing. |
| // however QUIC recovery draft 7.4 (Congestion Avoidance) limits |
| // the increase of cwnd to 1 max_datagram_size per cwnd acknowledged. |
| if r.cubic_state.cwnd_inc >= r.max_datagram_size { |
| r.congestion_window += r.max_datagram_size; |
| r.cubic_state.cwnd_inc = 0; |
| } |
| |
| eprintln!("t={:?} reno={} w_est={} w_cubic={} cwnd={}", t, r.cubic_state.reno_cwnd, r.cubic_state.w_est, r.cubic_state.w_cubic(t, r.max_datagram_size), r.congestion_window); |
| } |
| } |
| |
| fn congestion_event( |
| r: &mut Recovery, time_sent: Instant, epoch: packet::Epoch, now: Instant, |
| ) { |
| let in_congestion_recovery = r.in_congestion_recovery(time_sent); |
| |
| // Start a new congestion event if packet was sent after the |
| // start of the previous congestion recovery period. |
| if !in_congestion_recovery { |
| r.congestion_recovery_start_time = Some(now); |
| |
| // Fast convergence |
| if r.cubic_state.w_max < r.cubic_state.w_last_max { |
| r.cubic_state.w_last_max = r.cubic_state.w_max; |
| r.cubic_state.w_max = |
| r.cubic_state.w_max as f64 * (1.0 + BETA_CUBIC) / 2.0; |
| } else { |
| r.cubic_state.w_last_max = r.cubic_state.w_max; |
| } |
| |
| r.cubic_state.w_max = r.congestion_window as f64; |
| r.ssthresh = (r.congestion_window as f64 * BETA_CUBIC) as usize; |
| r.ssthresh = cmp::max( |
| r.ssthresh, |
| r.max_datagram_size * recovery::MINIMUM_WINDOW_PACKETS, |
| ); |
| r.congestion_window = r.ssthresh; |
| |
| r.cubic_state.k = if r.cubic_state.w_max < r.congestion_window as f64 { |
| 0.0 |
| } else { |
| r.cubic_state |
| .cubic_k(r.congestion_window, r.max_datagram_size) |
| }; |
| |
| r.cubic_state.cwnd_inc = |
| (r.cubic_state.cwnd_inc as f64 * BETA_CUBIC) as usize; |
| |
| r.cubic_state.w_est = r.congestion_window as f64; |
| r.cubic_state.alpha_aimd = ALPHA_AIMD; |
| r.cubic_state.reno_cwnd = (r.cubic_state.w_max * recovery::LOSS_REDUCTION_FACTOR) as usize; |
| |
| if r.hystart.in_lss(epoch) { |
| r.hystart.congestion_event(); |
| } |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use super::*; |
| use crate::recovery::hystart; |
| |
| #[test] |
| fn cubic_init() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| |
| let r = Recovery::new(&cfg); |
| |
| assert!(r.cwnd() > 0); |
| assert_eq!(r.bytes_in_flight, 0); |
| } |
| |
| #[test] |
| fn cubic_send() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| |
| let mut r = Recovery::new(&cfg); |
| |
| r.on_packet_sent_cc(1000, Instant::now()); |
| |
| assert_eq!(r.bytes_in_flight, 1000); |
| } |
| |
| #[test] |
| fn cubic_slow_start() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| |
| let mut r = Recovery::new(&cfg); |
| let now = Instant::now(); |
| |
| let p = recovery::Sent { |
| pkt_num: 0, |
| frames: vec![], |
| time_sent: now, |
| time_acked: None, |
| time_lost: None, |
| size: r.max_datagram_size, |
| ack_eliciting: true, |
| in_flight: true, |
| delivered: 0, |
| delivered_time: now, |
| recent_delivered_packet_sent_time: now, |
| is_app_limited: false, |
| has_data: false, |
| }; |
| |
| // Send initcwnd full MSS packets to become no longer app limited |
| for _ in 0..recovery::INITIAL_WINDOW_PACKETS { |
| r.on_packet_sent_cc(p.size, now); |
| } |
| |
| let cwnd_prev = r.cwnd(); |
| |
| let acked = vec![Acked { |
| pkt_num: p.pkt_num, |
| time_sent: p.time_sent, |
| size: p.size, |
| }]; |
| |
| r.on_packets_acked(acked, packet::EPOCH_APPLICATION, now); |
| |
| // Check if cwnd increased by packet size (slow start) |
| assert_eq!(r.cwnd(), cwnd_prev + p.size); |
| } |
| |
| #[test] |
| fn cubic_slow_start_abc_l() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| |
| let mut r = Recovery::new(&cfg); |
| let now = Instant::now(); |
| |
| let p = recovery::Sent { |
| pkt_num: 0, |
| frames: vec![], |
| time_sent: now, |
| time_acked: None, |
| time_lost: None, |
| size: r.max_datagram_size, |
| ack_eliciting: true, |
| in_flight: true, |
| delivered: 0, |
| delivered_time: now, |
| recent_delivered_packet_sent_time: now, |
| is_app_limited: false, |
| has_data: false, |
| }; |
| |
| // Send initcwnd full MSS packets to become no longer app limited |
| for _ in 0..recovery::INITIAL_WINDOW_PACKETS { |
| r.on_packet_sent_cc(p.size, now); |
| } |
| |
| let cwnd_prev = r.cwnd(); |
| |
| let acked = vec![ |
| Acked { |
| pkt_num: p.pkt_num, |
| time_sent: p.time_sent, |
| size: p.size * 3, |
| }, |
| Acked { |
| pkt_num: p.pkt_num, |
| time_sent: p.time_sent, |
| size: p.size * 3, |
| }, |
| Acked { |
| pkt_num: p.pkt_num, |
| time_sent: p.time_sent, |
| size: p.size * 3, |
| }, |
| ]; |
| |
| r.on_packets_acked(acked, packet::EPOCH_APPLICATION, now); |
| |
| // Acked 3 packets, but cwnd will increase 2 x mss. |
| assert_eq!(r.cwnd(), cwnd_prev + p.size * recovery::ABC_L); |
| } |
| |
| #[test] |
| fn cubic_congestion_event() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| |
| let mut r = Recovery::new(&cfg); |
| let now = Instant::now(); |
| let prev_cwnd = r.cwnd(); |
| |
| r.congestion_event(now, packet::EPOCH_APPLICATION, now); |
| |
| // In CUBIC, after congestion event, cwnd will be reduced by (1 - |
| // CUBIC_BETA) |
| assert_eq!(prev_cwnd as f64 * BETA_CUBIC, r.cwnd() as f64); |
| } |
| |
| #[test] |
| fn cubic_congestion_avoidance() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| |
| let mut r = Recovery::new(&cfg); |
| let mut now = Instant::now(); |
| let prev_cwnd = r.cwnd(); |
| |
| // Send initcwnd full MSS packets to become no longer app limited |
| for _ in 0..recovery::INITIAL_WINDOW_PACKETS { |
| r.on_packet_sent_cc(r.max_datagram_size, now); |
| } |
| |
| // Trigger congestion event to update ssthresh |
| r.congestion_event(now, packet::EPOCH_APPLICATION, now); |
| |
| // After congestion event, cwnd will be reduced. |
| let cur_cwnd = (prev_cwnd as f64 * BETA_CUBIC) as usize; |
| assert_eq!(r.cwnd(), cur_cwnd); |
| |
| // Shift current time by 1 RTT. |
| let rtt = Duration::from_millis(100); |
| r.update_rtt(rtt, Duration::from_millis(0), now); |
| |
| // Exit from the recovery. |
| now += rtt; |
| |
| // During Congestion Avoidance, it will take |
| // 5 ACKs to increase cwnd by 1 MSS. |
| for _ in 0..70 { |
| let acked = vec![Acked { |
| pkt_num: 0, |
| // To exit from recovery |
| time_sent: now, |
| size: r.max_datagram_size, |
| }]; |
| |
| r.on_packets_acked(acked, packet::EPOCH_APPLICATION, now); |
| now += rtt; |
| } |
| |
| assert_eq!(r.cwnd(), cur_cwnd + r.max_datagram_size); |
| } |
| |
| #[test] |
| fn cubic_collapse_cwnd_and_restart() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| |
| let mut r = Recovery::new(&cfg); |
| let now = Instant::now(); |
| |
| // Fill up bytes_in_flight to avoid app_limited=true |
| r.on_packet_sent_cc(30000, now); |
| |
| // Trigger congestion event to update ssthresh |
| r.congestion_event(now, packet::EPOCH_APPLICATION, now); |
| |
| // After persistent congestion, cwnd should be the minimum window |
| r.collapse_cwnd(); |
| assert_eq!( |
| r.cwnd(), |
| r.max_datagram_size * recovery::MINIMUM_WINDOW_PACKETS |
| ); |
| |
| let acked = vec![Acked { |
| pkt_num: 0, |
| // To exit from recovery |
| time_sent: now + Duration::from_millis(1), |
| size: r.max_datagram_size, |
| }]; |
| |
| r.on_packets_acked(acked, packet::EPOCH_APPLICATION, now); |
| |
| // Slow start again - cwnd will be increased by 1 MSS |
| assert_eq!( |
| r.cwnd(), |
| r.max_datagram_size * (recovery::MINIMUM_WINDOW_PACKETS + 1) |
| ); |
| } |
| |
| #[test] |
| fn cubic_hystart_limited_slow_start() { |
| let mut cfg = crate::Config::new(crate::PROTOCOL_VERSION).unwrap(); |
| cfg.set_cc_algorithm(recovery::CongestionControlAlgorithm::CUBIC); |
| cfg.enable_hystart(true); |
| |
| let mut r = Recovery::new(&cfg); |
| let now = Instant::now(); |
| let pkt_num = 0; |
| let epoch = packet::EPOCH_APPLICATION; |
| |
| let p = recovery::Sent { |
| pkt_num: 0, |
| frames: vec![], |
| time_sent: now, |
| time_acked: None, |
| time_lost: None, |
| size: r.max_datagram_size, |
| ack_eliciting: true, |
| in_flight: true, |
| delivered: 0, |
| delivered_time: now, |
| recent_delivered_packet_sent_time: now, |
| is_app_limited: false, |
| has_data: false, |
| }; |
| |
| // 1st round. |
| let n_rtt_sample = hystart::N_RTT_SAMPLE; |
| let pkts_1st_round = n_rtt_sample as u64; |
| r.hystart.start_round(pkt_num); |
| |
| let rtt_1st = 50; |
| |
| // Send 1st round packets. |
| for _ in 0..n_rtt_sample { |
| r.on_packet_sent_cc(p.size, now); |
| } |
| |
| // Receving Acks. |
| let now = now + Duration::from_millis(rtt_1st); |
| for _ in 0..n_rtt_sample { |
| r.update_rtt( |
| Duration::from_millis(rtt_1st), |
| Duration::from_millis(0), |
| now, |
| ); |
| |
| let acked = vec![Acked { |
| pkt_num: p.pkt_num, |
| time_sent: p.time_sent, |
| size: p.size, |
| }]; |
| |
| r.on_packets_acked(acked, epoch, now); |
| } |
| |
| // Not in LSS yet. |
| assert_eq!(r.hystart.lss_start_time().is_some(), false); |
| |
| // 2nd round. |
| r.hystart.start_round(pkts_1st_round * 2); |
| |
| let mut rtt_2nd = 100; |
| let now = now + Duration::from_millis(rtt_2nd); |
| |
| // Send 2nd round packets. |
| for _ in 0..n_rtt_sample { |
| r.on_packet_sent_cc(p.size, now); |
| } |
| |
| // Receving Acks. |
| // Last ack will cause to exit to LSS. |
| let mut cwnd_prev = r.cwnd(); |
| |
| for _ in 0..n_rtt_sample { |
| cwnd_prev = r.cwnd(); |
| r.update_rtt( |
| Duration::from_millis(rtt_2nd), |
| Duration::from_millis(0), |
| now, |
| ); |
| |
| let acked = vec![Acked { |
| pkt_num: p.pkt_num, |
| time_sent: p.time_sent, |
| size: p.size, |
| }]; |
| |
| r.on_packets_acked(acked, epoch, now); |
| |
| // Keep increasing RTT so that hystart exits to LSS. |
| rtt_2nd += 4; |
| } |
| |
| // Now we are in LSS. |
| assert_eq!(r.hystart.lss_start_time().is_some(), true); |
| assert_eq!(r.cwnd(), cwnd_prev + r.max_datagram_size); |
| |
| // Send a full cwnd. |
| r.on_packet_sent_cc(r.cwnd(), now); |
| |
| // Ack'ing 4 packets to increase cwnd by 1 MSS during LSS |
| cwnd_prev = r.cwnd(); |
| for _ in 0..4 { |
| let acked = vec![Acked { |
| pkt_num: p.pkt_num, |
| time_sent: p.time_sent, |
| size: p.size, |
| }]; |
| r.on_packets_acked(acked, epoch, now); |
| } |
| |
| // During LSS cwnd will be increased less than usual slow start. |
| assert_eq!(r.cwnd(), cwnd_prev + r.max_datagram_size); |
| } |
| } |