congestvpn/congestion_control.cpp

#include "congestion_control.hpp"
#include "VpnPeer.hpp"
#include "util.hpp"

CongestionController::CongestionController(const VpnPeer& peer):
    _peer(peer)
{
    _last_seqno = _peer.get_loss_logger().get_cur_seqno();
    _loss_based.bandwidth = 3e5; // 300kBps seems a good value to start with
    _loss_based.prev_tot_sent = _peer.get_tot_bytes_sent();
    clock_gettime(CLOCK_MONOTONIC, &_last_bucket_update);
    clock_gettime(CLOCK_MONOTONIC, &_loss_based.prev_time);
    update_params();
}

void CongestionController::update_lossbased() {
    const VpnPeer::LossReports& loss_rep = _peer.get_loss_reports();

    uint32_t delta_seqno = loss_rep.last_seqno - loss_rep.prev_seqno;
    unsigned int delta_losses = loss_rep.last_losses - loss_rep.prev_losses;

    double loss_rate = (double)delta_losses / (double)delta_seqno;

    struct timespec cur_time;
    clock_gettime(CLOCK_MONOTONIC, &cur_time);

    uint64_t cur_sent = _peer.get_tot_bytes_sent();

    double instant_bandwidth = /* byte per second */
        (double)(cur_sent - _loss_based.prev_tot_sent)
        / (double)(timespec_us_diff(cur_time, _loss_based.prev_time))
        * 1e6;

    _loss_based.prev_time = cur_time;
    _loss_based.prev_tot_sent = cur_sent;

    if(loss_rate < 0.02) {
        if(instant_bandwidth > 0.75 * _loss_based.bandwidth)
            _loss_based.bandwidth *= 1.05;
    }
    else if(loss_rate >= 0.1)
        _loss_based.bandwidth *= (1 - 0.5 * loss_rate);

    update_params();
}

void CongestionController::update_params() {
    _bandwidth = _loss_based.bandwidth; // meant to integrate other controllers
    _bucket_max_level = _bandwidth * _peer.get_rtt().avg_rtt();
    _bucket_level = std::min(_bucket_level, _bucket_max_level);
}