face: add best-effort link-layer reliability
refs #3931
Change-Id: I009fabe000f4dd4ceb62acab6b0c735c13112430
diff --git a/core/rtt-estimator.cpp b/core/rtt-estimator.cpp
new file mode 100644
index 0000000..8de3078
--- /dev/null
+++ b/core/rtt-estimator.cpp
@@ -0,0 +1,80 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014-2017, Regents of the University of California,
+ * Arizona Board of Regents,
+ * Colorado State University,
+ * University Pierre & Marie Curie, Sorbonne University,
+ * Washington University in St. Louis,
+ * Beijing Institute of Technology,
+ * The University of Memphis
+ *
+ * This file is part of NFD (Named Data Networking Forwarding Daemon).
+ * See AUTHORS.md for complete list of NFD authors and contributors.
+ *
+ * NFD is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation,
+ * either version 3 of the License, or (at your option) any later version.
+ *
+ * NFD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ * PURPOSE. See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * NFD, e.g., in COPYING.md file. If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+#include "rtt-estimator.hpp"
+
+namespace nfd {
+
+RttEstimator::RttEstimator(uint16_t maxMultiplier, Duration minRto, double gain)
+ : m_maxMultiplier(maxMultiplier)
+ , m_minRto(minRto.count())
+ , m_rtt(RttEstimator::getInitialRtt().count())
+ , m_gain(gain)
+ , m_variance(0)
+ , m_multiplier(1)
+ , m_nSamples(0)
+{
+}
+
+void
+RttEstimator::addMeasurement(Duration measure)
+{
+ double m = static_cast<double>(measure.count());
+ if (m_nSamples > 0) {
+ double err = m - m_rtt;
+ double gErr = err * m_gain;
+ m_rtt += gErr;
+ double difference = std::abs(err) - m_variance;
+ m_variance += difference * m_gain;
+ }
+ else {
+ m_rtt = m;
+ m_variance = m;
+ }
+ ++m_nSamples;
+ m_multiplier = 1;
+}
+
+void
+RttEstimator::incrementMultiplier()
+{
+ m_multiplier = std::min(static_cast<uint16_t>(m_multiplier + 1), m_maxMultiplier);
+}
+
+void
+RttEstimator::doubleMultiplier()
+{
+ m_multiplier = std::min(static_cast<uint16_t>(m_multiplier * 2), m_maxMultiplier);
+}
+
+RttEstimator::Duration
+RttEstimator::computeRto() const
+{
+ double rto = std::max(m_minRto, m_rtt + 4 * m_variance);
+ rto *= m_multiplier;
+ return Duration(static_cast<Duration::rep>(rto));
+}
+
+} // namespace nfd