65 lines
2.2 KiB
C++
65 lines
2.2 KiB
C++
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/*
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* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "net/dcsctp/tx/retransmission_timeout.h"
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#include <cmath>
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#include <cstdint>
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#include "net/dcsctp/public/dcsctp_options.h"
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namespace dcsctp {
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namespace {
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// https://tools.ietf.org/html/rfc4960#section-15
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constexpr double kRtoAlpha = 0.125;
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constexpr double kRtoBeta = 0.25;
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} // namespace
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RetransmissionTimeout::RetransmissionTimeout(const DcSctpOptions& options)
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: min_rto_(*options.rto_min),
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max_rto_(*options.rto_max),
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max_rtt_(*options.rtt_max),
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rto_(*options.rto_initial) {}
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void RetransmissionTimeout::ObserveRTT(DurationMs measured_rtt) {
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double rtt = *measured_rtt;
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// Unrealistic values will be skipped. If a wrongly measured (or otherwise
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// corrupt) value was processed, it could change the state in a way that would
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// take a very long time to recover.
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if (rtt < 0.0 || rtt > max_rtt_) {
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return;
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}
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if (first_measurement_) {
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// https://tools.ietf.org/html/rfc4960#section-6.3.1
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// "When the first RTT measurement R is made, set
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// SRTT <- R,
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// RTTVAR <- R/2, and
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// RTO <- SRTT + 4 * RTTVAR."
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srtt_ = rtt;
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rttvar_ = rtt * 0.5;
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rto_ = srtt_ + 4 * rttvar_;
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first_measurement_ = false;
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} else {
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// https://tools.ietf.org/html/rfc4960#section-6.3.1
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// "When a new RTT measurement R' is made, set
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// RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|
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// SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'
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// RTO <- SRTT + 4 * RTTVAR."
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rttvar_ = (1 - kRtoBeta) * rttvar_ + kRtoBeta * std::abs(srtt_ - rtt);
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srtt_ = (1 - kRtoAlpha) * srtt_ + kRtoAlpha * rtt;
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rto_ = srtt_ + 4 * rttvar_;
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}
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// Clamp RTO between min and max.
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rto_ = std::fmin(std::fmax(rto_, min_rto_), max_rto_);
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}
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} // namespace dcsctp
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