rtt-estimator.cpp

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/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
#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