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diff --git a/third_party/libwebrtc/net/dcsctp/tx/retransmission_timeout.h b/third_party/libwebrtc/net/dcsctp/tx/retransmission_timeout.h
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+++ b/third_party/libwebrtc/net/dcsctp/tx/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:
+  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_