quiche/src/recovery/bbr/init.rs

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use super::*;
use crate::recovery::Recovery;

use std::time::Duration;
use std::time::Instant;

// BBR Functions at Initialization.
//

// 4.3.1.  Initialization Steps
pub fn bbr_init(r: &mut Recovery) {
    let rtt = r.rtt();
    let bbr = &mut r.bbr_state;

    bbr.rtprop = rtt;
    bbr.rtprop_stamp = Instant::now();
    bbr.next_round_delivered = r.delivery_rate.delivered();

    r.send_quantum = r.max_datagram_size;

    bbr_init_round_counting(r);
    bbr_init_full_pipe(r);
    bbr_init_pacing_rate(r);
    bbr_enter_startup(r);
}

// 4.1.1.3.  Tracking Time for the BBR.BtlBw Max Filter
fn bbr_init_round_counting(r: &mut Recovery) {
    let bbr = &mut r.bbr_state;

    bbr.next_round_delivered = 0;
    bbr.round_start = false;
    bbr.round_count = 0;
}

// 4.2.1.  Pacing Rate
fn bbr_init_pacing_rate(r: &mut Recovery) {
    let bbr = &mut r.bbr_state;

    let srtt = r
        .smoothed_rtt
        .unwrap_or_else(|| Duration::from_millis(1))
        .as_secs_f64();

    // At init, cwnd is initcwnd.
    let nominal_bandwidth = r.congestion_window as f64 / srtt;

    bbr.pacing_rate = (bbr.pacing_gain * nominal_bandwidth) as u64;
}

// 4.3.2.1.  Startup Dynamics
pub fn bbr_enter_startup(r: &mut Recovery) {
    let bbr = &mut r.bbr_state;

    bbr.state = BBRStateMachine::Startup;
    bbr.pacing_gain = BBR_HIGH_GAIN;
    bbr.cwnd_gain = BBR_HIGH_GAIN;
}

// 4.3.2.2.  Estimating When Startup has Filled the Pipe
fn bbr_init_full_pipe(r: &mut Recovery) {
    let bbr = &mut r.bbr_state;

    bbr.filled_pipe = false;
    bbr.full_bw = 0;
    bbr.full_bw_count = 0;
}