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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.
*/
#ifndef NET_DCSCTP_TX_RETRANSMISSION_TIMEOUT_H_
#define NET_DCSCTP_TX_RETRANSMISSION_TIMEOUT_H_
#include <cstdint>
#include <functional>
#include "net/dcsctp/public/dcsctp_options.h"
namespace dcsctp {
// Manages updating of the Retransmission Timeout (RTO) SCTP variable, which is
// used directly as the base timeout for T3-RTX and for other timers, such as
// delayed ack.
//
// When a round-trip-time (RTT) is calculated (outside this class), `Observe`
// is called, which calculates the retransmission timeout (RTO) value. The RTO
// value will become larger if the RTT is high and/or the RTT values are varying
// a lot, which is an indicator of a bad connection.
class RetransmissionTimeout {
public:
static constexpr int kRttShift = 3;
static constexpr int kRttVarShift = 2;
explicit RetransmissionTimeout(const DcSctpOptions& options);
// To be called when a RTT has been measured, to update the RTO value.
void ObserveRTT(DurationMs measured_rtt);
// Returns the Retransmission Timeout (RTO) value, in milliseconds.
DurationMs rto() const { return DurationMs(rto_); }
// Returns the smoothed RTT value, in milliseconds.
DurationMs srtt() const { return DurationMs(scaled_srtt_ >> kRttShift); }
private:
const int32_t min_rto_;
const int32_t max_rto_;
const int32_t max_rtt_;
const int32_t min_rtt_variance_;
// If this is the first measurement
bool first_measurement_ = true;
// Smoothed Round-Trip Time, shifted by kRttShift
int32_t scaled_srtt_;
// Round-Trip Time Variation, shifted by kRttVarShift
int32_t scaled_rtt_var_ = 0;
// Retransmission Timeout
int32_t rto_;
};
} // namespace dcsctp
#endif // NET_DCSCTP_TX_RETRANSMISSION_TIMEOUT_H_
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