daemon/fw/asf-strategy.cpp - NFD - Gitiles

 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
  * Copyright (c) 2014-2018,  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 "asf-strategy.hpp"
 #include "algorithm.hpp"

 #include "core/logger.hpp"

 namespace nfd {
 namespace fw {
 namespace asf {

 NFD_LOG_INIT("AsfStrategy");
 NFD_REGISTER_STRATEGY(AsfStrategy);

 const time::milliseconds AsfStrategy::RETX_SUPPRESSION_INITIAL(10);
 const time::milliseconds AsfStrategy::RETX_SUPPRESSION_MAX(250);

 AsfStrategy::AsfStrategy(Forwarder& forwarder, const Name& name)
   : Strategy(forwarder)
   , m_measurements(getMeasurements())
   , m_probing(m_measurements)
   , m_maxSilentTimeouts(0)
   , m_retxSuppression(RETX_SUPPRESSION_INITIAL,
                       RetxSuppressionExponential::DEFAULT_MULTIPLIER,
                       RETX_SUPPRESSION_MAX)
 {
   ParsedInstanceName parsed = parseInstanceName(name);
   if (!parsed.parameters.empty()) {
     processParams(parsed.parameters);
   }

   if (parsed.version && *parsed.version != getStrategyName()[-1].toVersion()) {
     BOOST_THROW_EXCEPTION(std::invalid_argument(
       "AsfStrategy does not support version " + to_string(*parsed.version)));
   }
   this->setInstanceName(makeInstanceName(name, getStrategyName()));

   NFD_LOG_DEBUG("Probing interval=" << m_probing.getProbingInterval()
                 << ", Num silent timeouts=" << m_maxSilentTimeouts);
 }

 const Name&
 AsfStrategy::getStrategyName()
 {
   static Name strategyName("/localhost/nfd/strategy/asf/%FD%03");
   return strategyName;
 }

 void
 AsfStrategy::processParams(const PartialName& parsed)
 {
   for (const auto& component : parsed) {
     std::string parsedStr(reinterpret_cast<const char*>(component.value()), component.value_size());
     auto n = parsedStr.find("~");
     if (n == std::string::npos) {
       BOOST_THROW_EXCEPTION(std::invalid_argument("Format is <parameter>~<value>"));
     }

     auto f = parsedStr.substr(0, n);
     auto s = parsedStr.substr(n + 1);
     if (f == "probing-interval") {
       m_probing.setProbingInterval(getParamValue(f, s));
     }
     else if (f == "n-silent-timeouts") {
       m_maxSilentTimeouts = getParamValue(f, s);
     }
     else {
       BOOST_THROW_EXCEPTION(std::invalid_argument("Parameter should be probing-interval or n-silent-timeouts"));
     }
   }
 }

 uint64_t
 AsfStrategy::getParamValue(const std::string& param, const std::string& value)
 {
   try {
     if (!value.empty() && value[0] == '-')
       BOOST_THROW_EXCEPTION(boost::bad_lexical_cast());

     return boost::lexical_cast<uint64_t>(value);
   }
   catch (const boost::bad_lexical_cast&) {
     BOOST_THROW_EXCEPTION(std::invalid_argument("Value of " + param + " must be a non-negative integer"));
   }
 }

 void
 AsfStrategy::afterReceiveInterest(const Face& inFace, const Interest& interest,
                                   const shared_ptr<pit::Entry>& pitEntry)
 {
   // Should the Interest be suppressed?
   RetxSuppressionResult suppressResult = m_retxSuppression.decidePerPitEntry(*pitEntry);

   switch (suppressResult) {
   case RetxSuppressionResult::NEW:
   case RetxSuppressionResult::FORWARD:
     break;
   case RetxSuppressionResult::SUPPRESS:
     NFD_LOG_DEBUG(interest << " from=" << inFace.getId() << " suppressed");
     return;
   }

   const fib::Entry& fibEntry = this->lookupFib(*pitEntry);
   const fib::NextHopList& nexthops = fibEntry.getNextHops();

   if (nexthops.size() == 0) {
     sendNoRouteNack(inFace, interest, pitEntry);
     this->rejectPendingInterest(pitEntry);
     return;
   }

   Face* faceToUse = getBestFaceForForwarding(fibEntry, interest, inFace);

   if (faceToUse == nullptr) {
     sendNoRouteNack(inFace, interest, pitEntry);
     this->rejectPendingInterest(pitEntry);
     return;
   }

   NFD_LOG_TRACE("Forwarding interest to face: " << faceToUse->getId());

   forwardInterest(interest, fibEntry, pitEntry, *faceToUse);

   // If necessary, send probe
   if (m_probing.isProbingNeeded(fibEntry, interest)) {
     Face* faceToProbe = m_probing.getFaceToProbe(inFace, interest, fibEntry, *faceToUse);

     if (faceToProbe != nullptr) {
       bool wantNewNonce = true;
       forwardInterest(interest, fibEntry, pitEntry, *faceToProbe, wantNewNonce);
       m_probing.afterForwardingProbe(fibEntry, interest);
     }
   }
 }

 void
 AsfStrategy::beforeSatisfyInterest(const shared_ptr<pit::Entry>& pitEntry,
                                    const Face& inFace, const Data& data)
 {
   NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(pitEntry->getName());

   if (namespaceInfo == nullptr) {
     NFD_LOG_TRACE("Could not find measurements entry for " << pitEntry->getName());
     return;
   }

   // Record the RTT between the Interest out to Data in
   FaceInfo* faceInfo = namespaceInfo->get(inFace.getId());
   if (faceInfo == nullptr) {
     return;
   }
   faceInfo->recordRtt(pitEntry, inFace);

   // Extend lifetime for measurements associated with Face
   namespaceInfo->extendFaceInfoLifetime(*faceInfo, inFace.getId());

   if (faceInfo->isTimeoutScheduled()) {
     faceInfo->cancelTimeoutEvent(data.getName());
   }
 }

 void
 AsfStrategy::afterReceiveNack(const Face& inFace, const lp::Nack& nack,
                               const shared_ptr<pit::Entry>& pitEntry)
 {
   NFD_LOG_DEBUG("Nack for " << nack.getInterest() << " from=" << inFace.getId() << ": " << nack.getReason());
   onTimeout(pitEntry->getName(), inFace.getId());
 }

 ////////////////////////////////////////////////////////////////////////////////
 ////////////////////////////////////////////////////////////////////////////////

 void
 AsfStrategy::forwardInterest(const Interest& interest,
                              const fib::Entry& fibEntry,
                              const shared_ptr<pit::Entry>& pitEntry,
                              Face& outFace,
                              bool wantNewNonce)
 {
   if (wantNewNonce) {
     //Send probe: interest with new Nonce
     Interest probeInterest(interest);
     probeInterest.refreshNonce();
     NFD_LOG_TRACE("Sending probe for " << probeInterest << probeInterest.getNonce()
                                        << " to FaceId: " << outFace.getId());
     this->sendInterest(pitEntry, outFace, probeInterest);
   }
   else {
     this->sendInterest(pitEntry, outFace, interest);
   }

   FaceInfo& faceInfo = m_measurements.getOrCreateFaceInfo(fibEntry, interest, outFace.getId());

   // Refresh measurements since Face is being used for forwarding
   NamespaceInfo& namespaceInfo = m_measurements.getOrCreateNamespaceInfo(fibEntry, interest);
   namespaceInfo.extendFaceInfoLifetime(faceInfo, outFace.getId());

   if (!faceInfo.isTimeoutScheduled()) {
     // Estimate and schedule timeout
     RttEstimator::Duration timeout = faceInfo.computeRto();

     NFD_LOG_TRACE("Scheduling timeout for " << fibEntry.getPrefix()
                                             << " FaceId: " << outFace.getId()
                                             << " in " << time::duration_cast<time::milliseconds>(timeout) << " ms");

     scheduler::EventId id = scheduler::schedule(timeout,
         bind(&AsfStrategy::onTimeout, this, interest.getName(), outFace.getId()));

     faceInfo.setTimeoutEvent(id, interest.getName());
   }
 }

 struct FaceStats
 {
   Face* face;
   RttStats::Rtt rtt;
   RttStats::Rtt srtt;
   uint64_t cost;
 };

 double
 getValueForSorting(const FaceStats& stats)
 {
   // These values allow faces with no measurements to be ranked better than timeouts
   // srtt < RTT_NO_MEASUREMENT < RTT_TIMEOUT
   static const RttStats::Rtt SORTING_RTT_TIMEOUT = time::microseconds::max();
   static const RttStats::Rtt SORTING_RTT_NO_MEASUREMENT = SORTING_RTT_TIMEOUT / 2;

   if (stats.rtt == RttStats::RTT_TIMEOUT) {
     return SORTING_RTT_TIMEOUT.count();
   }
   else if (stats.rtt == RttStats::RTT_NO_MEASUREMENT) {
     return SORTING_RTT_NO_MEASUREMENT.count();
   }
   else {
     return stats.srtt.count();
   }
 }

 Face*
 AsfStrategy::getBestFaceForForwarding(const fib::Entry& fibEntry, const Interest& interest,
                                       const Face& inFace)
 {
   NFD_LOG_TRACE("Looking for best face for " << fibEntry.getPrefix());

   typedef std::function<bool(const FaceStats&, const FaceStats&)> FaceStatsPredicate;
   typedef std::set<FaceStats, FaceStatsPredicate> FaceStatsSet;

   FaceStatsSet rankedFaces(
     [] (const FaceStats& lhs, const FaceStats& rhs) -> bool {
       // Sort by RTT and then by cost
       double lhsValue = getValueForSorting(lhs);
       double rhsValue = getValueForSorting(rhs);

       if (lhsValue < rhsValue) {
         return true;
       }
       else if (lhsValue == rhsValue) {
         return lhs.cost < rhs.cost;
       }
       else {
         return false;
       }
   });

   for (const fib::NextHop& hop : fibEntry.getNextHops()) {
     Face& hopFace = hop.getFace();

     if ((hopFace.getId() == inFace.getId() && hopFace.getLinkType() != ndn::nfd::LINK_TYPE_AD_HOC) ||
          wouldViolateScope(inFace, interest, hopFace)) {
       continue;
     }

     FaceInfo* info = m_measurements.getFaceInfo(fibEntry, interest, hopFace.getId());

     if (info == nullptr) {
       FaceStats stats = {&hopFace,
                          RttStats::RTT_NO_MEASUREMENT,
                          RttStats::RTT_NO_MEASUREMENT,
                          hop.getCost()};

       rankedFaces.insert(stats);
     }
     else {
       FaceStats stats = {&hopFace, info->getRtt(), info->getSrtt(), hop.getCost()};
       rankedFaces.insert(stats);
     }
   }

   FaceStatsSet::iterator it = rankedFaces.begin();

   if (it != rankedFaces.end()) {
     return it->face;
   }
   else {
     return nullptr;
   }
 }

 void
 AsfStrategy::onTimeout(const Name& interestName, const face::FaceId faceId)
 {
   NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(interestName);

   if (namespaceInfo == nullptr) {
     NFD_LOG_TRACE("FibEntry for " << interestName << " has been removed since timeout scheduling");
     return;
   }

   FaceInfoTable::iterator it = namespaceInfo->find(faceId);

   if (it == namespaceInfo->end()) {
     it = namespaceInfo->insert(faceId);
   }

   FaceInfo& faceInfo = it->second;

   faceInfo.setNSilentTimeouts(faceInfo.getNSilentTimeouts() + 1);

   if (faceInfo.getNSilentTimeouts() <= m_maxSilentTimeouts) {
     NFD_LOG_TRACE("FaceId " << faceId << " for " << interestName << " has timed-out "
                   << faceInfo.getNSilentTimeouts() << " time(s), ignoring");
     // Extend lifetime for measurements associated with Face
     namespaceInfo->extendFaceInfoLifetime(faceInfo, faceId);

     if (faceInfo.isTimeoutScheduled()) {
       faceInfo.cancelTimeoutEvent(interestName);
     }
   }
   else {
     NFD_LOG_TRACE("FaceId " << faceId << " for " << interestName << " has timed-out");
     faceInfo.recordTimeout(interestName);
   }
 }

 void
 AsfStrategy::sendNoRouteNack(const Face& inFace, const Interest& interest,
                              const shared_ptr<pit::Entry>& pitEntry)
 {
   NFD_LOG_DEBUG(interest << " from=" << inFace.getId() << " noNextHop");

   lp::NackHeader nackHeader;
   nackHeader.setReason(lp::NackReason::NO_ROUTE);
   this->sendNack(pitEntry, inFace, nackHeader);
 }

 } // namespace asf
 } // namespace fw
 } // namespace nfd
	/* -- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -- */
	/*
	* Copyright (c) 2014-2018, 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 "asf-strategy.hpp"
	#include "algorithm.hpp"

	#include "core/logger.hpp"

	namespace nfd {
	namespace fw {
	namespace asf {

	NFD_LOG_INIT("AsfStrategy");
	NFD_REGISTER_STRATEGY(AsfStrategy);

	const time::milliseconds AsfStrategy::RETX_SUPPRESSION_INITIAL(10);
	const time::milliseconds AsfStrategy::RETX_SUPPRESSION_MAX(250);

	AsfStrategy::AsfStrategy(Forwarder& forwarder, const Name& name)
	: Strategy(forwarder)
	, m_measurements(getMeasurements())
	, m_probing(m_measurements)
	, m_maxSilentTimeouts(0)
	, m_retxSuppression(RETX_SUPPRESSION_INITIAL,
	RetxSuppressionExponential::DEFAULT_MULTIPLIER,
	RETX_SUPPRESSION_MAX)
	{
	ParsedInstanceName parsed = parseInstanceName(name);
	if (!parsed.parameters.empty()) {
	processParams(parsed.parameters);
	}

	if (parsed.version && *parsed.version != getStrategyName()[-1].toVersion()) {
	BOOST_THROW_EXCEPTION(std::invalid_argument(
	"AsfStrategy does not support version " + to_string(*parsed.version)));
	}
	this->setInstanceName(makeInstanceName(name, getStrategyName()));

	NFD_LOG_DEBUG("Probing interval=" << m_probing.getProbingInterval()
	<< ", Num silent timeouts=" << m_maxSilentTimeouts);
	}

	const Name&
	AsfStrategy::getStrategyName()
	{
	static Name strategyName("/localhost/nfd/strategy/asf/%FD%03");
	return strategyName;
	}

	void
	AsfStrategy::processParams(const PartialName& parsed)
	{
	for (const auto& component : parsed) {
	std::string parsedStr(reinterpret_cast<const char*>(component.value()), component.value_size());
	auto n = parsedStr.find("~");
	if (n == std::string::npos) {
	BOOST_THROW_EXCEPTION(std::invalid_argument("Format is <parameter>~<value>"));
	}

	auto f = parsedStr.substr(0, n);
	auto s = parsedStr.substr(n + 1);
	if (f == "probing-interval") {
	m_probing.setProbingInterval(getParamValue(f, s));
	}
	else if (f == "n-silent-timeouts") {
	m_maxSilentTimeouts = getParamValue(f, s);
	}
	else {
	BOOST_THROW_EXCEPTION(std::invalid_argument("Parameter should be probing-interval or n-silent-timeouts"));
	}
	}
	}

	uint64_t
	AsfStrategy::getParamValue(const std::string& param, const std::string& value)
	{
	try {
	if (!value.empty() && value[0] == '-')
	BOOST_THROW_EXCEPTION(boost::bad_lexical_cast());

	return boost::lexical_cast<uint64_t>(value);
	}
	catch (const boost::bad_lexical_cast&) {
	BOOST_THROW_EXCEPTION(std::invalid_argument("Value of " + param + " must be a non-negative integer"));
	}
	}

	void
	AsfStrategy::afterReceiveInterest(const Face& inFace, const Interest& interest,
	const shared_ptr<pit::Entry>& pitEntry)
	{
	// Should the Interest be suppressed?
	RetxSuppressionResult suppressResult = m_retxSuppression.decidePerPitEntry(*pitEntry);

	switch (suppressResult) {
	case RetxSuppressionResult::NEW:
	case RetxSuppressionResult::FORWARD:
	break;
	case RetxSuppressionResult::SUPPRESS:
	NFD_LOG_DEBUG(interest << " from=" << inFace.getId() << " suppressed");
	return;
	}

	const fib::Entry& fibEntry = this->lookupFib(*pitEntry);
	const fib::NextHopList& nexthops = fibEntry.getNextHops();

	if (nexthops.size() == 0) {
	sendNoRouteNack(inFace, interest, pitEntry);
	this->rejectPendingInterest(pitEntry);
	return;
	}

	Face* faceToUse = getBestFaceForForwarding(fibEntry, interest, inFace);

	if (faceToUse == nullptr) {
	sendNoRouteNack(inFace, interest, pitEntry);
	this->rejectPendingInterest(pitEntry);
	return;
	}

	NFD_LOG_TRACE("Forwarding interest to face: " << faceToUse->getId());

	forwardInterest(interest, fibEntry, pitEntry, *faceToUse);

	// If necessary, send probe
	if (m_probing.isProbingNeeded(fibEntry, interest)) {
	Face* faceToProbe = m_probing.getFaceToProbe(inFace, interest, fibEntry, *faceToUse);

	if (faceToProbe != nullptr) {
	bool wantNewNonce = true;
	forwardInterest(interest, fibEntry, pitEntry, *faceToProbe, wantNewNonce);
	m_probing.afterForwardingProbe(fibEntry, interest);
	}
	}
	}

	void
	AsfStrategy::beforeSatisfyInterest(const shared_ptr<pit::Entry>& pitEntry,
	const Face& inFace, const Data& data)
	{
	NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(pitEntry->getName());

	if (namespaceInfo == nullptr) {
	NFD_LOG_TRACE("Could not find measurements entry for " << pitEntry->getName());
	return;
	}

	// Record the RTT between the Interest out to Data in
	FaceInfo* faceInfo = namespaceInfo->get(inFace.getId());
	if (faceInfo == nullptr) {
	return;
	}
	faceInfo->recordRtt(pitEntry, inFace);

	// Extend lifetime for measurements associated with Face
	namespaceInfo->extendFaceInfoLifetime(*faceInfo, inFace.getId());

	if (faceInfo->isTimeoutScheduled()) {
	faceInfo->cancelTimeoutEvent(data.getName());
	}
	}

	void
	AsfStrategy::afterReceiveNack(const Face& inFace, const lp::Nack& nack,
	const shared_ptr<pit::Entry>& pitEntry)
	{
	NFD_LOG_DEBUG("Nack for " << nack.getInterest() << " from=" << inFace.getId() << ": " << nack.getReason());
	onTimeout(pitEntry->getName(), inFace.getId());
	}

	////////////////////////////////////////////////////////////////////////////////
	////////////////////////////////////////////////////////////////////////////////

	void
	AsfStrategy::forwardInterest(const Interest& interest,
	const fib::Entry& fibEntry,
	const shared_ptr<pit::Entry>& pitEntry,
	Face& outFace,
	bool wantNewNonce)
	{
	if (wantNewNonce) {
	//Send probe: interest with new Nonce
	Interest probeInterest(interest);
	probeInterest.refreshNonce();
	NFD_LOG_TRACE("Sending probe for " << probeInterest << probeInterest.getNonce()
	<< " to FaceId: " << outFace.getId());
	this->sendInterest(pitEntry, outFace, probeInterest);
	}
	else {
	this->sendInterest(pitEntry, outFace, interest);
	}

	FaceInfo& faceInfo = m_measurements.getOrCreateFaceInfo(fibEntry, interest, outFace.getId());

	// Refresh measurements since Face is being used for forwarding
	NamespaceInfo& namespaceInfo = m_measurements.getOrCreateNamespaceInfo(fibEntry, interest);
	namespaceInfo.extendFaceInfoLifetime(faceInfo, outFace.getId());

	if (!faceInfo.isTimeoutScheduled()) {
	// Estimate and schedule timeout
	RttEstimator::Duration timeout = faceInfo.computeRto();

	NFD_LOG_TRACE("Scheduling timeout for " << fibEntry.getPrefix()
	<< " FaceId: " << outFace.getId()
	<< " in " << time::duration_cast<time::milliseconds>(timeout) << " ms");

	scheduler::EventId id = scheduler::schedule(timeout,
	bind(&AsfStrategy::onTimeout, this, interest.getName(), outFace.getId()));

	faceInfo.setTimeoutEvent(id, interest.getName());
	}
	}

	struct FaceStats
	{
	Face* face;
	RttStats::Rtt rtt;
	RttStats::Rtt srtt;
	uint64_t cost;
	};

	double
	getValueForSorting(const FaceStats& stats)
	{
	// These values allow faces with no measurements to be ranked better than timeouts
	// srtt < RTT_NO_MEASUREMENT < RTT_TIMEOUT
	static const RttStats::Rtt SORTING_RTT_TIMEOUT = time::microseconds::max();
	static const RttStats::Rtt SORTING_RTT_NO_MEASUREMENT = SORTING_RTT_TIMEOUT / 2;

	if (stats.rtt == RttStats::RTT_TIMEOUT) {
	return SORTING_RTT_TIMEOUT.count();
	}
	else if (stats.rtt == RttStats::RTT_NO_MEASUREMENT) {
	return SORTING_RTT_NO_MEASUREMENT.count();
	}
	else {
	return stats.srtt.count();
	}
	}

	Face*
	AsfStrategy::getBestFaceForForwarding(const fib::Entry& fibEntry, const Interest& interest,
	const Face& inFace)
	{
	NFD_LOG_TRACE("Looking for best face for " << fibEntry.getPrefix());

	typedef std::function<bool(const FaceStats&, const FaceStats&)> FaceStatsPredicate;
	typedef std::set<FaceStats, FaceStatsPredicate> FaceStatsSet;

	FaceStatsSet rankedFaces(
	[] (const FaceStats& lhs, const FaceStats& rhs) -> bool {
	// Sort by RTT and then by cost
	double lhsValue = getValueForSorting(lhs);
	double rhsValue = getValueForSorting(rhs);

	if (lhsValue < rhsValue) {
	return true;
	}
	else if (lhsValue == rhsValue) {
	return lhs.cost < rhs.cost;
	}
	else {
	return false;
	}
	});

	for (const fib::NextHop& hop : fibEntry.getNextHops()) {
	Face& hopFace = hop.getFace();

	if ((hopFace.getId() == inFace.getId() && hopFace.getLinkType() != ndn::nfd::LINK_TYPE_AD_HOC) \|\|
	wouldViolateScope(inFace, interest, hopFace)) {
	continue;
	}

	FaceInfo* info = m_measurements.getFaceInfo(fibEntry, interest, hopFace.getId());

	if (info == nullptr) {
	FaceStats stats = {&hopFace,
	RttStats::RTT_NO_MEASUREMENT,
	RttStats::RTT_NO_MEASUREMENT,
	hop.getCost()};

	rankedFaces.insert(stats);
	}
	else {
	FaceStats stats = {&hopFace, info->getRtt(), info->getSrtt(), hop.getCost()};
	rankedFaces.insert(stats);
	}
	}

	FaceStatsSet::iterator it = rankedFaces.begin();

	if (it != rankedFaces.end()) {
	return it->face;
	}
	else {
	return nullptr;
	}
	}

	void
	AsfStrategy::onTimeout(const Name& interestName, const face::FaceId faceId)
	{
	NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(interestName);

	if (namespaceInfo == nullptr) {
	NFD_LOG_TRACE("FibEntry for " << interestName << " has been removed since timeout scheduling");
	return;
	}

	FaceInfoTable::iterator it = namespaceInfo->find(faceId);

	if (it == namespaceInfo->end()) {
	it = namespaceInfo->insert(faceId);
	}

	FaceInfo& faceInfo = it->second;

	faceInfo.setNSilentTimeouts(faceInfo.getNSilentTimeouts() + 1);

	if (faceInfo.getNSilentTimeouts() <= m_maxSilentTimeouts) {
	NFD_LOG_TRACE("FaceId " << faceId << " for " << interestName << " has timed-out "
	<< faceInfo.getNSilentTimeouts() << " time(s), ignoring");
	// Extend lifetime for measurements associated with Face
	namespaceInfo->extendFaceInfoLifetime(faceInfo, faceId);

	if (faceInfo.isTimeoutScheduled()) {
	faceInfo.cancelTimeoutEvent(interestName);
	}
	}
	else {
	NFD_LOG_TRACE("FaceId " << faceId << " for " << interestName << " has timed-out");
	faceInfo.recordTimeout(interestName);
	}
	}

	void
	AsfStrategy::sendNoRouteNack(const Face& inFace, const Interest& interest,
	const shared_ptr<pit::Entry>& pitEntry)
	{
	NFD_LOG_DEBUG(interest << " from=" << inFace.getId() << " noNextHop");

	lp::NackHeader nackHeader;
	nackHeader.setReason(lp::NackReason::NO_ROUTE);
	this->sendNack(pitEntry, inFace, nackHeader);
	}

	} // namespace asf
	} // namespace fw
	} // namespace nfd