Aimd pipelining in Segment fetcher

src/net/named_data/jndn/util/RttEstimator.java

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+/**
+ * Copyright (C) 2015-2019 Regents of the University of California.
+ *
+ * @author: Ritik Kumar <[email protected]>
+ * @author: From ndn-cxx util/segment-fetcher https://github.com/named-data/ndn-cxx
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ * A copy of the GNU Lesser General Public License is in the file COPYING.
+ */
+
+package net.named_data.jndn.util;
+
+/**
+ * RTTEstimator is a utility class which uses Round-Trip times to calculates retransmission timeout
+ *
+ * This class implements the "Mean-Deviation" RTT estimator, as discussed in RFC 6298,
+ * with the modifications to RTO calculation described in RFC 7323 Appendix G.
+ */
+
+public class RttEstimator {
+
+    public static class Options {
+
+        /** weight of exponential moving average for smoothed RTT
+         */
+        public double alpha = 0.125;
+        /** weight of exponential moving average for RTT variation
+         */
+        public double beta = 0.25;
+        /** initial RTO value in milliseconds
+         */
+        public double initialRto = 1000.0;
+        /** lower bound of RTO in milliseconds
+         */
+        public double minRto = 200.0;
+        /** upper bound of RTO in milliseconds
+         */
+        public double maxRto = 60000.0;
+        /** RTT vaiation multiplier used when calculating RTO
+         */
+        public int k = 4;
+        /** RTO multiplier used in backoff operation
+         */
+        public int rtoBackoffMultiplier = 2;
+
+    }
+
+    /**
+     * Creates an RTT estimator.
+     *
+     * Configures the RTT estimator with the default parameters.
+     */
+    public RttEstimator() {
+        this(new Options());
+    }
+
+    /**
+     * Create an RTT Estimator
+     *
+     * Configures the RTT Estimator
+     * @param options_ Parameters for configuration.
+     */
+    RttEstimator(Options options_) {
+        this.options_ = options_;
+        rto_ = options_.initialRto;
+    }
+
+    /**
+     * Record a new RTT measurement.
+     *
+     * @param rtt the sampled RTT
+     * @param nExpectedSamples number of expected samples, must be greater than 0.
+     *        It should be set to the current number of in-flight Interests. Please
+     *        refer to Appendix G of RFC 7323 for details.
+     * NOTE: Do not call this function with RTT samples from retransmitted Interests
+     *       (per Karn's algorithm).
+     */
+    void
+    addMeasurement(double rtt, int nExpectedSamples) {
+        if (nRttSamples_ == 0) { // first measurement
+            sRtt_ = rtt;
+            rttVar_ = sRtt_ / 2;
+        }
+        else {
+            double alpha = options_.alpha / nExpectedSamples;
+            double beta = options_.beta / nExpectedSamples;
+            rttVar_ = (1 - beta) * rttVar_ + beta * Math.abs(sRtt_ - rtt);
+            sRtt_ = (1 - alpha) * sRtt_ + alpha * rtt;
+        }
+
+        rto_ = sRtt_ + options_.k * rttVar_;
+        rto_ = clamp(rto_, options_.minRto, options_.maxRto);
+
+        rttAvg_ = (nRttSamples_ * rttAvg_ + rtt) / (nRttSamples_ + 1);
+        rttMax_ = Math.max(rtt, rttMax_);
+        rttMin_ = Math.max(rtt, rttMin_);
+        nRttSamples_++;
+    }
+
+    /**
+     * Backoff RTO by a factor of Options.rtoBackoffMultiplier.
+     */
+    void
+    backoffRto()
+    {
+        rto_ = clamp(rto_ * options_.rtoBackoffMultiplier,
+                options_.minRto, options_.maxRto);
+    }
+
+
+    private static double clamp
+    (double val, double min, double max) {
+        return Math.max(min, Math.min(max, val));
+    }
+
+    /**
+     * Returns the estimated RTO value.
+     */
+    double
+    getEstimatedRto()
+    {
+        return rto_;
+    }
+
+    /**
+     * Returns the minimum RTT observed.
+     */
+    double
+    getMinRtt()
+    {
+        return rttMin_;
+    }
+
+    /**
+     * Returns the maximum RTT observed.
+     */
+    double
+    getMaxRtt()
+    {
+        return rttMax_;
+    }
+
+    /**
+     * Returns the average RTT.
+     */
+    double
+    getAvgRtt()
+    {
+        return rttAvg_;
+    }
+
+    private final Options options_;
+    private double sRtt_ = Double.NaN; // smoothed round-trip time
+    private double rttVar_ =  Double.NaN; // round-trip time variation
+    private double rto_ = 0; // retransmission timeout
+    private double rttMin_ = Double.MAX_VALUE;
+    private double rttMax_ = Double.MIN_VALUE;
+    private double rttAvg_ = 0.0;
+    private long nRttSamples_ = 0; // number of RTT samples
+}