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

 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
  * Copyright (c) 2014-2019,  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 "common/global.hpp"
 #include "common/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_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()) {
     NDN_THROW(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()
                 << " n-silent-timeouts=" << m_maxSilentTimeouts);
 }

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

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

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

 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) {
       NDN_THROW(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 {
       NDN_THROW(std::invalid_argument("Parameter should be probing-interval or n-silent-timeouts"));
     }
   }
 }

 void
 AsfStrategy::afterReceiveInterest(const FaceEndpoint& ingress, const Interest& interest,
                                   const shared_ptr<pit::Entry>& pitEntry)
 {
   // Should the Interest be suppressed?
   auto suppressResult = m_retxSuppression.decidePerPitEntry(*pitEntry);
   if (suppressResult == RetxSuppressionResult::SUPPRESS) {
     NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " suppressed");
     return;
   }

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

   if (suppressResult == RetxSuppressionResult::NEW) {
     if (nexthops.size() == 0) {
       NFD_LOG_DEBUG(interest << " new-interest from=" << ingress << " no-nexthop");
       sendNoRouteNack(ingress, pitEntry);
       return;
     }

     Face* faceToUse = getBestFaceForForwarding(interest, ingress.face, fibEntry, pitEntry);
     if (faceToUse != nullptr) {
       NFD_LOG_DEBUG(interest << " new-interest from=" << ingress << " forward-to=" << faceToUse->getId());
       forwardInterest(interest, *faceToUse, fibEntry, pitEntry);

       // If necessary, send probe
       sendProbe(interest, ingress, *faceToUse, fibEntry, pitEntry);
     }
     else {
       NFD_LOG_DEBUG(interest << " new-interest from=" << ingress << " no-nexthop");
       sendNoRouteNack(ingress, pitEntry);
     }
     return;
   }

   Face* faceToUse = getBestFaceForForwarding(interest, ingress.face, fibEntry, pitEntry, false);
   // if unused face not found, select nexthop with earliest out record
   if (faceToUse != nullptr) {
     NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " forward-to=" << faceToUse->getId());
     forwardInterest(interest, *faceToUse, fibEntry, pitEntry);
     // avoid probing in case of forwarding
     return;
   }

   // find an eligible upstream that is used earliest
   auto it = nexthops.end();
   it = findEligibleNextHopWithEarliestOutRecord(ingress.face, interest, nexthops, pitEntry);
   if (it == nexthops.end()) {
     NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " no-nexthop");
   }
   else {
     auto egress = FaceEndpoint(it->getFace(), 0);
     NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " retry-to=" << egress);
     this->sendInterest(pitEntry, egress, interest);
   }
 }

 void
 AsfStrategy::beforeSatisfyInterest(const shared_ptr<pit::Entry>& pitEntry,
                                    const FaceEndpoint& ingress, const Data& data)
 {
   NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(pitEntry->getName());
   if (namespaceInfo == nullptr) {
     NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress << " no-measurements");
     return;
   }

   // Record the RTT between the Interest out to Data in
   FaceInfo* faceInfo = namespaceInfo->getFaceInfo(ingress.face.getId());
   if (faceInfo == nullptr) {
     NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress << " no-face-info");
     return;
   }

   auto outRecord = pitEntry->getOutRecord(ingress.face);
   if (outRecord == pitEntry->out_end()) {
     NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress << " no-out-record");
   }
   else {
     faceInfo->recordRtt(time::steady_clock::now() - outRecord->getLastRenewed());
     NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress
                   << " rtt=" << faceInfo->getLastRtt() << " srtt=" << faceInfo->getSrtt());
   }

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

   faceInfo->cancelTimeout(data.getName());
 }

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

 void
 AsfStrategy::forwardInterest(const Interest& interest, Face& outFace, const fib::Entry& fibEntry,
                              const shared_ptr<pit::Entry>& pitEntry, bool wantNewNonce)
 {
   auto egress = FaceEndpoint(outFace, 0);
   if (wantNewNonce) {
     // Send probe: interest with new Nonce
     Interest probeInterest(interest);
     probeInterest.refreshNonce();
     NFD_LOG_TRACE("Sending probe for " << probeInterest << " to=" << egress);
     this->sendInterest(pitEntry, egress, probeInterest);
   }
   else {
     this->sendInterest(pitEntry, egress, interest);
   }

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

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

   if (!faceInfo.isTimeoutScheduled()) {
     auto timeout = faceInfo.scheduleTimeout(interest.getName(),
       [this, name = interest.getName(), faceId = egress.face.getId()] {
         onTimeout(name, faceId);
       });
     NFD_LOG_TRACE("Scheduled timeout for " << fibEntry.getPrefix() << " to=" << egress
                   << " in " << time::duration_cast<time::milliseconds>(timeout) << " ms");
   }
 }

 void
 AsfStrategy::sendProbe(const Interest& interest, const FaceEndpoint& ingress, const Face& faceToUse,
                        const fib::Entry& fibEntry, const shared_ptr<pit::Entry>& pitEntry)
 {
   if (!m_probing.isProbingNeeded(fibEntry, interest))
     return;

   Face* faceToProbe = m_probing.getFaceToProbe(ingress.face, interest, fibEntry, faceToUse);
   if (faceToProbe == nullptr)
     return;

   forwardInterest(interest, *faceToProbe, fibEntry, pitEntry, true);
   m_probing.afterForwardingProbe(fibEntry, interest);
 }

 struct FaceStats
 {
   Face* face;
   time::nanoseconds rtt;
   time::nanoseconds srtt;
   uint64_t cost;
 };

 struct FaceStatsCompare
 {
   bool
   operator()(const FaceStats& lhs, const FaceStats& rhs) const
   {
     time::nanoseconds lhsValue = getValueForSorting(lhs);
     time::nanoseconds rhsValue = getValueForSorting(rhs);

     // Sort by RTT and then by cost
     return std::tie(lhsValue, lhs.cost) < std::tie(rhsValue, rhs.cost);
   }

 private:
   static time::nanoseconds
   getValueForSorting(const FaceStats& stats)
   {
     // These values allow faces with no measurements to be ranked better than timeouts
     // srtt < RTT_NO_MEASUREMENT < RTT_TIMEOUT
     if (stats.rtt == FaceInfo::RTT_TIMEOUT) {
       return time::nanoseconds::max();
     }
     else if (stats.rtt == FaceInfo::RTT_NO_MEASUREMENT) {
       return time::nanoseconds::max() / 2;
     }
     else {
       return stats.srtt;
     }
   }
 };

 Face*
 AsfStrategy::getBestFaceForForwarding(const Interest& interest, const Face& inFace,
                                       const fib::Entry& fibEntry, const shared_ptr<pit::Entry>& pitEntry,
                                       bool isInterestNew)
 {
   std::set<FaceStats, FaceStatsCompare> rankedFaces;

   auto now = time::steady_clock::now();
   for (const auto& nh : fibEntry.getNextHops()) {
     if (!isNextHopEligible(inFace, interest, nh, pitEntry, !isInterestNew, now)) {
       continue;
     }

     FaceInfo* info = m_measurements.getFaceInfo(fibEntry, interest, nh.getFace().getId());
     if (info == nullptr) {
       rankedFaces.insert({&nh.getFace(), FaceInfo::RTT_NO_MEASUREMENT,
                           FaceInfo::RTT_NO_MEASUREMENT, nh.getCost()});
     }
     else {
       rankedFaces.insert({&nh.getFace(), info->getLastRtt(), info->getSrtt(), nh.getCost()});
     }
   }

   auto it = rankedFaces.begin();
   return it != rankedFaces.end() ? it->face : nullptr;
 }

 void
 AsfStrategy::onTimeout(const Name& interestName, FaceId faceId)
 {
   NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(interestName);
   if (namespaceInfo == nullptr) {
     NFD_LOG_TRACE(interestName << " FibEntry has been removed since timeout scheduling");
     return;
   }

   FaceInfo* fiPtr = namespaceInfo->getFaceInfo(faceId);
   if (fiPtr == nullptr) {
     NFD_LOG_TRACE(interestName << " FaceInfo id=" << faceId << " has been removed since timeout scheduling");
     return;
   }

   auto& faceInfo = *fiPtr;
   size_t nTimeouts = faceInfo.getNSilentTimeouts() + 1;
   faceInfo.setNSilentTimeouts(nTimeouts);

   if (nTimeouts <= m_maxSilentTimeouts) {
     NFD_LOG_TRACE(interestName << " face=" << faceId << " timeout-count=" << nTimeouts << " ignoring");
     // Extend lifetime for measurements associated with Face
     namespaceInfo->extendFaceInfoLifetime(faceInfo, faceId);
     faceInfo.cancelTimeout(interestName);
   }
   else {
     NFD_LOG_TRACE(interestName << " face=" << faceId << " timeout-count=" << nTimeouts);
     faceInfo.recordTimeout(interestName);
   }
 }

 void
 AsfStrategy::sendNoRouteNack(const FaceEndpoint& ingress, const shared_ptr<pit::Entry>& pitEntry)
 {
   lp::NackHeader nackHeader;
   nackHeader.setReason(lp::NackReason::NO_ROUTE);
   this->sendNack(pitEntry, ingress, nackHeader);
   this->rejectPendingInterest(pitEntry);
 }

 } // namespace asf
 } // namespace fw
 } // namespace nfd
	/* -- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -- */
	/*
	* Copyright (c) 2014-2019, 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 "common/global.hpp"
	#include "common/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_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()) {
	NDN_THROW(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()
	<< " n-silent-timeouts=" << m_maxSilentTimeouts);
	}

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

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

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

	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) {
	NDN_THROW(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 {
	NDN_THROW(std::invalid_argument("Parameter should be probing-interval or n-silent-timeouts"));
	}
	}
	}

	void
	AsfStrategy::afterReceiveInterest(const FaceEndpoint& ingress, const Interest& interest,
	const shared_ptr<pit::Entry>& pitEntry)
	{
	// Should the Interest be suppressed?
	auto suppressResult = m_retxSuppression.decidePerPitEntry(*pitEntry);
	if (suppressResult == RetxSuppressionResult::SUPPRESS) {
	NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " suppressed");
	return;
	}

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

	if (suppressResult == RetxSuppressionResult::NEW) {
	if (nexthops.size() == 0) {
	NFD_LOG_DEBUG(interest << " new-interest from=" << ingress << " no-nexthop");
	sendNoRouteNack(ingress, pitEntry);
	return;
	}

	Face* faceToUse = getBestFaceForForwarding(interest, ingress.face, fibEntry, pitEntry);
	if (faceToUse != nullptr) {
	NFD_LOG_DEBUG(interest << " new-interest from=" << ingress << " forward-to=" << faceToUse->getId());
	forwardInterest(interest, *faceToUse, fibEntry, pitEntry);

	// If necessary, send probe
	sendProbe(interest, ingress, *faceToUse, fibEntry, pitEntry);
	}
	else {
	NFD_LOG_DEBUG(interest << " new-interest from=" << ingress << " no-nexthop");
	sendNoRouteNack(ingress, pitEntry);
	}
	return;
	}

	Face* faceToUse = getBestFaceForForwarding(interest, ingress.face, fibEntry, pitEntry, false);
	// if unused face not found, select nexthop with earliest out record
	if (faceToUse != nullptr) {
	NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " forward-to=" << faceToUse->getId());
	forwardInterest(interest, *faceToUse, fibEntry, pitEntry);
	// avoid probing in case of forwarding
	return;
	}

	// find an eligible upstream that is used earliest
	auto it = nexthops.end();
	it = findEligibleNextHopWithEarliestOutRecord(ingress.face, interest, nexthops, pitEntry);
	if (it == nexthops.end()) {
	NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " no-nexthop");
	}
	else {
	auto egress = FaceEndpoint(it->getFace(), 0);
	NFD_LOG_DEBUG(interest << " retx-interest from=" << ingress << " retry-to=" << egress);
	this->sendInterest(pitEntry, egress, interest);
	}
	}

	void
	AsfStrategy::beforeSatisfyInterest(const shared_ptr<pit::Entry>& pitEntry,
	const FaceEndpoint& ingress, const Data& data)
	{
	NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(pitEntry->getName());
	if (namespaceInfo == nullptr) {
	NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress << " no-measurements");
	return;
	}

	// Record the RTT between the Interest out to Data in
	FaceInfo* faceInfo = namespaceInfo->getFaceInfo(ingress.face.getId());
	if (faceInfo == nullptr) {
	NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress << " no-face-info");
	return;
	}

	auto outRecord = pitEntry->getOutRecord(ingress.face);
	if (outRecord == pitEntry->out_end()) {
	NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress << " no-out-record");
	}
	else {
	faceInfo->recordRtt(time::steady_clock::now() - outRecord->getLastRenewed());
	NFD_LOG_DEBUG(pitEntry->getName() << " data from=" << ingress
	<< " rtt=" << faceInfo->getLastRtt() << " srtt=" << faceInfo->getSrtt());
	}

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

	faceInfo->cancelTimeout(data.getName());
	}

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

	void
	AsfStrategy::forwardInterest(const Interest& interest, Face& outFace, const fib::Entry& fibEntry,
	const shared_ptr<pit::Entry>& pitEntry, bool wantNewNonce)
	{
	auto egress = FaceEndpoint(outFace, 0);
	if (wantNewNonce) {
	// Send probe: interest with new Nonce
	Interest probeInterest(interest);
	probeInterest.refreshNonce();
	NFD_LOG_TRACE("Sending probe for " << probeInterest << " to=" << egress);
	this->sendInterest(pitEntry, egress, probeInterest);
	}
	else {
	this->sendInterest(pitEntry, egress, interest);
	}

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

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

	if (!faceInfo.isTimeoutScheduled()) {
	auto timeout = faceInfo.scheduleTimeout(interest.getName(),
	[this, name = interest.getName(), faceId = egress.face.getId()] {
	onTimeout(name, faceId);
	});
	NFD_LOG_TRACE("Scheduled timeout for " << fibEntry.getPrefix() << " to=" << egress
	<< " in " << time::duration_cast<time::milliseconds>(timeout) << " ms");
	}
	}

	void
	AsfStrategy::sendProbe(const Interest& interest, const FaceEndpoint& ingress, const Face& faceToUse,
	const fib::Entry& fibEntry, const shared_ptr<pit::Entry>& pitEntry)
	{
	if (!m_probing.isProbingNeeded(fibEntry, interest))
	return;

	Face* faceToProbe = m_probing.getFaceToProbe(ingress.face, interest, fibEntry, faceToUse);
	if (faceToProbe == nullptr)
	return;

	forwardInterest(interest, *faceToProbe, fibEntry, pitEntry, true);
	m_probing.afterForwardingProbe(fibEntry, interest);
	}

	struct FaceStats
	{
	Face* face;
	time::nanoseconds rtt;
	time::nanoseconds srtt;
	uint64_t cost;
	};

	struct FaceStatsCompare
	{
	bool
	operator()(const FaceStats& lhs, const FaceStats& rhs) const
	{
	time::nanoseconds lhsValue = getValueForSorting(lhs);
	time::nanoseconds rhsValue = getValueForSorting(rhs);

	// Sort by RTT and then by cost
	return std::tie(lhsValue, lhs.cost) < std::tie(rhsValue, rhs.cost);
	}

	private:
	static time::nanoseconds
	getValueForSorting(const FaceStats& stats)
	{
	// These values allow faces with no measurements to be ranked better than timeouts
	// srtt < RTT_NO_MEASUREMENT < RTT_TIMEOUT
	if (stats.rtt == FaceInfo::RTT_TIMEOUT) {
	return time::nanoseconds::max();
	}
	else if (stats.rtt == FaceInfo::RTT_NO_MEASUREMENT) {
	return time::nanoseconds::max() / 2;
	}
	else {
	return stats.srtt;
	}
	}
	};

	Face*
	AsfStrategy::getBestFaceForForwarding(const Interest& interest, const Face& inFace,
	const fib::Entry& fibEntry, const shared_ptr<pit::Entry>& pitEntry,
	bool isInterestNew)
	{
	std::set<FaceStats, FaceStatsCompare> rankedFaces;

	auto now = time::steady_clock::now();
	for (const auto& nh : fibEntry.getNextHops()) {
	if (!isNextHopEligible(inFace, interest, nh, pitEntry, !isInterestNew, now)) {
	continue;
	}

	FaceInfo* info = m_measurements.getFaceInfo(fibEntry, interest, nh.getFace().getId());
	if (info == nullptr) {
	rankedFaces.insert({&nh.getFace(), FaceInfo::RTT_NO_MEASUREMENT,
	FaceInfo::RTT_NO_MEASUREMENT, nh.getCost()});
	}
	else {
	rankedFaces.insert({&nh.getFace(), info->getLastRtt(), info->getSrtt(), nh.getCost()});
	}
	}

	auto it = rankedFaces.begin();
	return it != rankedFaces.end() ? it->face : nullptr;
	}

	void
	AsfStrategy::onTimeout(const Name& interestName, FaceId faceId)
	{
	NamespaceInfo* namespaceInfo = m_measurements.getNamespaceInfo(interestName);
	if (namespaceInfo == nullptr) {
	NFD_LOG_TRACE(interestName << " FibEntry has been removed since timeout scheduling");
	return;
	}

	FaceInfo* fiPtr = namespaceInfo->getFaceInfo(faceId);
	if (fiPtr == nullptr) {
	NFD_LOG_TRACE(interestName << " FaceInfo id=" << faceId << " has been removed since timeout scheduling");
	return;
	}

	auto& faceInfo = *fiPtr;
	size_t nTimeouts = faceInfo.getNSilentTimeouts() + 1;
	faceInfo.setNSilentTimeouts(nTimeouts);

	if (nTimeouts <= m_maxSilentTimeouts) {
	NFD_LOG_TRACE(interestName << " face=" << faceId << " timeout-count=" << nTimeouts << " ignoring");
	// Extend lifetime for measurements associated with Face
	namespaceInfo->extendFaceInfoLifetime(faceInfo, faceId);
	faceInfo.cancelTimeout(interestName);
	}
	else {
	NFD_LOG_TRACE(interestName << " face=" << faceId << " timeout-count=" << nTimeouts);
	faceInfo.recordTimeout(interestName);
	}
	}

	void
	AsfStrategy::sendNoRouteNack(const FaceEndpoint& ingress, const shared_ptr<pit::Entry>& pitEntry)
	{
	lp::NackHeader nackHeader;
	nackHeader.setReason(lp::NackReason::NO_ROUTE);
	this->sendNack(pitEntry, ingress, nackHeader);
	this->rejectPendingInterest(pitEntry);
	}

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