1 files changed, 63 insertions, 0 deletions
diff --git a/third_party/libwebrtc/net/dcsctp/tx/retransmission_timeout.cc b/third_party/libwebrtc/net/dcsctp/tx/retransmission_timeout.cc
new file mode 100644
index 0000000000..7d8fb9761c
--- /dev/null
+++ b/third_party/libwebrtc/net/dcsctp/tx/retransmission_timeout.cc
@@ -0,0 +1,63 @@
+/*
+ *  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 "net/dcsctp/public/dcsctp_options.h"
+
+namespace dcsctp {
+
+RetransmissionTimeout::RetransmissionTimeout(const DcSctpOptions& options)
+    : min_rto_(*options.rto_min),
+      max_rto_(*options.rto_max),
+      max_rtt_(*options.rtt_max),
+      min_rtt_variance_(*options.min_rtt_variance),
+      scaled_srtt_(*options.rto_initial << kRttShift),
+      rto_(*options.rto_initial) {}
+
+void RetransmissionTimeout::ObserveRTT(DurationMs measured_rtt) {
+  const int32_t rtt = *measured_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 < 0 || rtt > max_rtt_) {
+    return;
+  }
+
+  // From https://tools.ietf.org/html/rfc4960#section-6.3.1, but avoiding
+  // floating point math by implementing algorithm from "V. Jacobson: Congestion
+  // avoidance and control", but adapted for SCTP.
+  if (first_measurement_) {
+    scaled_srtt_ = rtt << kRttShift;
+    scaled_rtt_var_ = (rtt / 2) << kRttVarShift;
+    first_measurement_ = false;
+  } else {
+    int32_t rtt_diff = rtt - (scaled_srtt_ >> kRttShift);
+    scaled_srtt_ += rtt_diff;
+    if (rtt_diff < 0) {
+      rtt_diff = -rtt_diff;
+    }
+    rtt_diff -= (scaled_rtt_var_ >> kRttVarShift);
+    scaled_rtt_var_ += rtt_diff;
+  }
+
+  if (scaled_rtt_var_ < min_rtt_variance_) {
+    scaled_rtt_var_ = min_rtt_variance_;
+  }
+
+  rto_ = (scaled_srtt_ >> kRttShift) + scaled_rtt_var_;
+
+  // Clamp RTO between min and max.
+  rto_ = std::min(std::max(rto_, min_rto_), max_rto_);
+}
+}  // namespace dcsctp