retransmission_timeout.h

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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:

  explicit RetransmissionTimeout(const DcSctpOptions& options);

  // To be called when a RTT has been measured, to update the RTO value.

  void ObserveRTT(webrtc::TimeDelta rtt);

  // Returns the Retransmission Timeout (RTO) value.

  webrtc::TimeDelta rto() const { return rto_; }

  // Returns the smoothed RTT value.

  webrtc::TimeDelta srtt() const { return srtt_; }

 private:

  const webrtc::TimeDelta min_rto_;

  const webrtc::TimeDelta max_rto_;

  const webrtc::TimeDelta max_rtt_;

  const webrtc::TimeDelta min_rtt_variance_;

  // If this is the first measurement

  bool first_measurement_ = true;

  // Smoothed Round-Trip Time.

  webrtc::TimeDelta srtt_;

  // Round-Trip Time Variation.

  webrtc::TimeDelta rtt_var_ = webrtc::TimeDelta::Zero();

  // Retransmission Timeout

  webrtc::TimeDelta rto_;

};

}  // namespace dcsctp

#endif  // NET_DCSCTP_TX_RETRANSMISSION_TIMEOUT_H_