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/*
* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "net/dcsctp/tx/retransmission_timeout.h"
#include <algorithm>
#include <cstdint>
#include "api/units/time_delta.h"
#include "net/dcsctp/public/dcsctp_options.h"
namespace dcsctp {
constexpr double kRtoAlpha = 0.125;
constexpr double kRtoBeta = 0.25;
// A factor that the `min_rtt_variance` configuration option will be divided by
// (before later multiplied with K, which is 4 according to RFC6298). When this
// value was introduced, it was unintentionally divided by 8 since that code
// worked with scaled numbers (to avoid floating point math). That behavior is
// kept as downstream users have measured good values for their use-cases.
constexpr double kHeuristicVarianceAdjustment = 8.0;
RetransmissionTimeout::RetransmissionTimeout(const DcSctpOptions& options)
: min_rto_(options.rto_min.ToTimeDelta()),
max_rto_(options.rto_max.ToTimeDelta()),
max_rtt_(options.rtt_max.ToTimeDelta()),
min_rtt_variance_(options.min_rtt_variance.ToTimeDelta() /
kHeuristicVarianceAdjustment),
srtt_(options.rto_initial.ToTimeDelta()),
rto_(options.rto_initial.ToTimeDelta()) {}
void RetransmissionTimeout::ObserveRTT(webrtc::TimeDelta rtt) {
// Unrealistic values will be skipped. If a wrongly measured (or otherwise
// corrupt) value was processed, it could change the state in a way that would
// take a very long time to recover.
if (rtt < webrtc::TimeDelta::Zero() || rtt > max_rtt_) {
return;
}
if (first_measurement_) {
srtt_ = rtt;
rtt_var_ = rtt / 2;
first_measurement_ = false;
} else {
webrtc::TimeDelta rtt_diff = (srtt_ - rtt).Abs();
rtt_var_ = (1 - kRtoBeta) * rtt_var_ + kRtoBeta * rtt_diff;
srtt_ = (1 - kRtoAlpha) * srtt_ + kRtoAlpha * rtt;
}
if (rtt_var_ < min_rtt_variance_) {
rtt_var_ = min_rtt_variance_;
}
rto_ = srtt_ + 4 * rtt_var_;
rto_ = std::clamp(rto_, min_rto_, max_rto_);
}
} // namespace dcsctp