fw: RttEstimator
refs #1568
Change-Id: Ife59d8d4715e293aec44f8fbe24582bb684452c4
diff --git a/daemon/fw/rtt-estimator.cpp b/daemon/fw/rtt-estimator.cpp
new file mode 100644
index 0000000..97b2ab0
--- /dev/null
+++ b/daemon/fw/rtt-estimator.cpp
@@ -0,0 +1,79 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014 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
diff --git a/daemon/fw/rtt-estimator.hpp b/daemon/fw/rtt-estimator.hpp
new file mode 100644
index 0000000..a830c5a
--- /dev/null
+++ b/daemon/fw/rtt-estimator.hpp
@@ -0,0 +1,83 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014 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/>.
+ **/
+
+#ifndef NFD_DAEMON_FW_RTT_ESTIMATOR_HPP
+#define NFD_DAEMON_FW_RTT_ESTIMATOR_HPP
+
+#include "common.hpp"
+
+namespace nfd {
+
+/**
+ * \brief implements the Mean-Deviation RTT estimator
+ *
+ * reference: ns3::RttMeanDeviation
+ *
+ * This RttEstimator algorithm is designed for TCP, which is a continuous stream.
+ * NDN Interest-Data traffic is not always a continuous stream,
+ * so NDN may need a different RttEstimator.
+ * The design of a more suitable RttEstimator is a research question.
+ */
+class RttEstimator
+{
+public:
+ typedef time::microseconds Duration;
+
+ static Duration
+ getInitialRtt(void)
+ {
+ return time::seconds(1);
+ }
+
+ RttEstimator(uint16_t maxMultiplier = 16,
+ Duration minRto = time::milliseconds(1),
+ double gain = 0.1);
+
+ void
+ addMeasurement(Duration measure);
+
+ void
+ incrementMultiplier();
+
+ void
+ doubleMultiplier();
+
+ Duration
+ computeRto() const;
+
+private:
+ uint16_t m_maxMultiplier;
+ double m_minRto;
+
+ double m_rtt;
+ double m_gain;
+ double m_variance;
+ uint16_t m_multiplier;
+ uint32_t m_nSamples;
+};
+
+} // namespace nfd
+
+#endif // NFD_DAEMON_FW_RTT_ESTIMATOR_HPP