diff --git a/core/common.hpp b/core/common.hpp
index 07971f1..dd6d4fb 100644
--- a/core/common.hpp
+++ b/core/common.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2020,  Regents of the University of California,
+ * Copyright (c) 2014-2021,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -43,20 +43,15 @@
 #include <functional>
 #include <iostream>
 #include <limits>
-#include <map>
 #include <memory>
 #include <stdexcept>
 #include <string>
 #include <utility>
 #include <vector>
 
-#include <boost/asio.hpp>
 #include <boost/assert.hpp>
 #include <boost/core/noncopyable.hpp>
 #include <boost/lexical_cast.hpp>
-#include <boost/program_options/options_description.hpp>
-#include <boost/program_options/variables_map.hpp>
-#include <boost/program_options/parsers.hpp>
 
 #include <ndn-cxx/data.hpp>
 #include <ndn-cxx/face.hpp>
@@ -66,7 +61,6 @@
 #include <ndn-cxx/util/backports.hpp>
 #include <ndn-cxx/util/exception.hpp>
 #include <ndn-cxx/util/scheduler.hpp>
-#include <ndn-cxx/util/signal.hpp>
 #include <ndn-cxx/util/time.hpp>
 
 namespace ndn {
@@ -80,8 +74,6 @@
 
 using boost::noncopyable;
 
-namespace signal = util::signal;
-
 } // namespace ndn
 
 #endif // NDN_TOOLS_CORE_COMMON_HPP
diff --git a/tests/chunks/producer.t.cpp b/tests/chunks/producer.t.cpp
index 6934fa4..ef53422 100644
--- a/tests/chunks/producer.t.cpp
+++ b/tests/chunks/producer.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2020,  Regents of the University of California,
+ * Copyright (c) 2016-2021,  Regents of the University of California,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University.
  *
@@ -26,6 +26,7 @@
 #include "tools/chunks/putchunks/producer.hpp"
 
 #include "tests/test-common.hpp"
+#include "tests/io-fixture.hpp"
 #include "tests/key-chain-fixture.hpp"
 
 #include <ndn-cxx/metadata-object.hpp>
@@ -42,32 +43,26 @@
 
 using namespace ndn::tests;
 
-class ProducerFixture : public KeyChainFixture
+class ProducerFixture : public IoFixture, public KeyChainFixture
 {
 protected:
   ProducerFixture()
-    : face(io, {true, true})
-    , prefix("/ndn/chunks/test")
-    , version(1449227841747)
-    , keyLocatorName(m_keyChain.createIdentity("/ProducerFixture").getDefaultKey().getName())
-    , testString(std::string(
-        "Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aenean commodo ligula eget "
-        "dolor. Aenean massa. Cum sociis natoque penatibus et magnis dis parturient montes, "
-        "nascetur ridiculus mus. Donec quam felis, ultricies nec, pellentesque eu, pretium quis, "
-        "sem. Nulla consequat massa Donec pede justo,"))
   {
     options.maxSegmentSize = 40;
     options.isQuiet = true;
   }
 
 protected:
-  boost::asio::io_service io;
-  util::DummyClientFace face;
-  Name prefix;
+  util::DummyClientFace face{m_io, {true, true}};
+  Name prefix = "/ndn/chunks/test";
   Producer::Options options;
-  uint64_t version;
-  Name keyLocatorName;
-  std::istringstream testString;
+  uint64_t version = 1449227841747;
+  Name keyLocatorName = m_keyChain.createIdentity("/ProducerFixture").getDefaultKey().getName();
+  std::istringstream testString{
+    "Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aenean commodo ligula eget "
+    "dolor. Aenean massa. Cum sociis natoque penatibus et magnis dis parturient montes, "
+    "nascetur ridiculus mus. Donec quam felis, ultricies nec, pellentesque eu, pretium quis, "
+    "sem. Nulla consequat massa Donec pede justo,"s};
 };
 
 BOOST_AUTO_TEST_SUITE(Chunks)
@@ -94,8 +89,9 @@
     Producer prod(prefix, face, m_keyChain, input, options);
 
     size_t expectedSize = std::ceil(static_cast<double>(testStrings[i].size()) / options.maxSegmentSize);
-    if (testStrings[i].empty())
+    if (testStrings[i].empty()) {
       expectedSize = 1;
+    }
 
     BOOST_CHECK_EQUAL(prod.m_store.size(), expectedSize);
   }
@@ -104,7 +100,7 @@
 BOOST_AUTO_TEST_CASE(RequestSegmentUnspecifiedVersion)
 {
   Producer producer(prefix, face, m_keyChain, testString, options);
-  io.poll();
+  m_io.poll();
   size_t nSegments = std::ceil(static_cast<double>(testString.str().size()) / options.maxSegmentSize);
 
   // version request
@@ -137,7 +133,7 @@
 BOOST_AUTO_TEST_CASE(RequestSegmentSpecifiedVersion)
 {
   Producer producer(prefix.appendVersion(version), face, m_keyChain, testString, options);
-  io.poll();
+  m_io.poll();
   size_t nSegments = std::ceil(static_cast<double>(testString.str().size()) / options.maxSegmentSize);
 
   // version request
@@ -171,7 +167,7 @@
 BOOST_AUTO_TEST_CASE(RequestNotExistingSegment)
 {
   Producer producer(prefix, face, m_keyChain, testString, options);
-  io.poll();
+  m_io.poll();
   size_t nSegments = std::ceil(static_cast<double>(testString.str().size()) / options.maxSegmentSize);
 
   // version request
@@ -198,7 +194,7 @@
 BOOST_AUTO_TEST_CASE(RequestMetadata)
 {
   Producer producer(prefix.appendVersion(version), face, m_keyChain, testString, options);
-  io.poll();
+  m_io.poll();
 
   // ask for metadata with a valid discovery interest
   face.receive(MetadataObject::makeDiscoveryInterest(Name(prefix).getPrefix(-1)));
diff --git a/tools/chunks/catchunks/consumer.hpp b/tools/chunks/catchunks/consumer.hpp
index 9972d76..3f6f77e 100644
--- a/tools/chunks/catchunks/consumer.hpp
+++ b/tools/chunks/catchunks/consumer.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2020, Regents of the University of California,
+ * Copyright (c) 2016-2021, Regents of the University of California,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University.
  *
@@ -34,6 +34,8 @@
 #include <ndn-cxx/security/validation-error.hpp>
 #include <ndn-cxx/security/validator.hpp>
 
+#include <map>
+
 namespace ndn {
 namespace chunks {
 
diff --git a/tools/chunks/catchunks/discover-version.hpp b/tools/chunks/catchunks/discover-version.hpp
index aaf409a..62a5e42 100644
--- a/tools/chunks/catchunks/discover-version.hpp
+++ b/tools/chunks/catchunks/discover-version.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2019, Regents of the University of California,
+ * Copyright (c) 2016-2021, Regents of the University of California,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University.
  *
@@ -31,6 +31,8 @@
 
 #include "options.hpp"
 
+#include <ndn-cxx/util/signal.hpp>
+
 namespace ndn {
 namespace chunks {
 
@@ -44,23 +46,19 @@
  */
 class DiscoverVersion
 {
-public: // signals
-  /**
-   * @brief Signal emitted when the versioned name of Data is found.
-   */
-  signal::Signal<DiscoverVersion, Name> onDiscoverySuccess;
-
-  /**
-   * @brief Signal emitted when a failure occurs.
-   */
-  signal::Signal<DiscoverVersion, std::string> onDiscoveryFailure;
-
 public:
   DiscoverVersion(Face& face, const Name& prefix, const Options& options);
 
   /**
-   * @brief identify the latest Data version published.
+   * @brief Signal emitted when the versioned name of Data is found.
    */
+  util::Signal<DiscoverVersion, Name> onDiscoverySuccess;
+
+  /**
+   * @brief Signal emitted when a failure occurs.
+   */
+  util::Signal<DiscoverVersion, std::string> onDiscoveryFailure;
+
   void
   run();
 
diff --git a/tools/chunks/catchunks/main.cpp b/tools/chunks/catchunks/main.cpp
index cfb4124..faa7ed6 100644
--- a/tools/chunks/catchunks/main.cpp
+++ b/tools/chunks/catchunks/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2020, Regents of the University of California,
+ * Copyright (c) 2016-2021, Regents of the University of California,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University.
  *
@@ -40,6 +40,10 @@
 #include <fstream>
 #include <ndn-cxx/security/validator-null.hpp>
 
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
+
 namespace ndn {
 namespace chunks {
 
diff --git a/tools/chunks/catchunks/pipeline-interests-adaptive.hpp b/tools/chunks/catchunks/pipeline-interests-adaptive.hpp
index 914143c..158656e 100644
--- a/tools/chunks/catchunks/pipeline-interests-adaptive.hpp
+++ b/tools/chunks/catchunks/pipeline-interests-adaptive.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2019, Regents of the University of California,
+ * Copyright (c) 2016-2021, Regents of the University of California,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University.
  *
@@ -32,6 +32,7 @@
 #include "pipeline-interests.hpp"
 
 #include <ndn-cxx/util/rtt-estimator.hpp>
+#include <ndn-cxx/util/signal.hpp>
 
 #include <queue>
 #include <unordered_map>
@@ -94,7 +95,7 @@
    * The callback function should be: `void(nanoseconds age, double cwnd)`, where `age` is the
    * time since the pipeline started and `cwnd` is the new congestion window size (in segments).
    */
-  signal::Signal<PipelineInterestsAdaptive, time::nanoseconds, double> afterCwndChange;
+  util::Signal<PipelineInterestsAdaptive, time::nanoseconds, double> afterCwndChange;
 
   struct RttSample
   {
@@ -108,7 +109,7 @@
   /**
    * @brief Signals when a new RTT sample has been taken.
    */
-  signal::Signal<PipelineInterestsAdaptive, RttSample> afterRttMeasurement;
+  util::Signal<PipelineInterestsAdaptive, RttSample> afterRttMeasurement;
 
 protected:
   DECLARE_SIGNAL_EMIT(afterCwndChange)
diff --git a/tools/chunks/catchunks/pipeline-interests.cpp b/tools/chunks/catchunks/pipeline-interests.cpp
index ad8b818..9f2e3b5 100644
--- a/tools/chunks/catchunks/pipeline-interests.cpp
+++ b/tools/chunks/catchunks/pipeline-interests.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2019, Regents of the University of California,
+ * Copyright (c) 2016-2021, Regents of the University of California,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University.
  *
@@ -31,6 +31,8 @@
 #include "pipeline-interests.hpp"
 #include "data-fetcher.hpp"
 
+#include <boost/asio/io_service.hpp>
+
 namespace ndn {
 namespace chunks {
 
diff --git a/tools/chunks/putchunks/main.cpp b/tools/chunks/putchunks/main.cpp
index 5e1dd9f..e1b0ea5 100644
--- a/tools/chunks/putchunks/main.cpp
+++ b/tools/chunks/putchunks/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2016-2019, Regents of the University of California,
+ * Copyright (c) 2016-2021, Regents of the University of California,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University.
  *
@@ -30,11 +30,15 @@
 #include "core/version.hpp"
 #include "producer.hpp"
 
-namespace po = boost::program_options;
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
 
 namespace ndn {
 namespace chunks {
 
+namespace po = boost::program_options;
+
 static void
 usage(std::ostream& os, const std::string& programName, const po::options_description& desc)
 {
diff --git a/tools/dissect/main.cpp b/tools/dissect/main.cpp
index a2a7034..fb14692 100644
--- a/tools/dissect/main.cpp
+++ b/tools/dissect/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California.
+ * Copyright (c) 2014-2021,  Regents of the University of California.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -21,16 +21,16 @@
 #include "core/version.hpp"
 
 #include <boost/program_options/options_description.hpp>
-#include <boost/program_options/variables_map.hpp>
 #include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
 
 #include <fstream>
 
-namespace po = boost::program_options;
-
 namespace ndn {
 namespace dissect {
 
+namespace po = boost::program_options;
+
 static void
 usage(std::ostream& os, const std::string& appName, const po::options_description& options)
 {
@@ -43,34 +43,27 @@
 static int
 main(int argc, char* argv[])
 {
+  std::string inputFileName;
+
   po::options_description visibleOptions;
   visibleOptions.add_options()
-    ("help,h", "Print help and exit.")
-    ("version,V", "Print version and exit.")
+    ("help,h",    "print help and exit")
+    ("version,V", "print version and exit")
     ;
 
-  std::string inputFileName;
   po::options_description hiddenOptions;
   hiddenOptions.add_options()
     ("input-file", po::value<std::string>(&inputFileName));
-  ;
-  po::positional_options_description positionalArguments;
-  positionalArguments
-    .add("input-file", -1);
 
   po::options_description allOptions;
-  allOptions
-    .add(visibleOptions)
-    .add(hiddenOptions)
-    ;
+  allOptions.add(visibleOptions).add(hiddenOptions);
+
+  po::positional_options_description pos;
+  pos.add("input-file", -1);
 
   po::variables_map vm;
   try {
-    po::store(po::command_line_parser(argc, argv)
-                .options(allOptions)
-                .positional(positionalArguments)
-                .run(),
-              vm);
+    po::store(po::command_line_parser(argc, argv).options(allOptions).positional(pos).run(), vm);
     po::notify(vm);
   }
   catch (const po::error& e) {
diff --git a/tools/dissect/ndn-dissect.cpp b/tools/dissect/ndn-dissect.cpp
index c072c69..907eef6 100644
--- a/tools/dissect/ndn-dissect.cpp
+++ b/tools/dissect/ndn-dissect.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2019, Regents of the University of California.
+ * Copyright (c) 2013-2021, Regents of the University of California.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -24,6 +24,7 @@
 #include "ndn-dissect.hpp"
 
 #include <algorithm>
+#include <map>
 
 #include <ndn-cxx/name-component.hpp>
 #include <ndn-cxx/encoding/tlv.hpp>
diff --git a/tools/dump/main.cpp b/tools/dump/main.cpp
index 86a9a85..49ea5b0 100644
--- a/tools/dump/main.cpp
+++ b/tools/dump/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2011-2019,  Regents of the University of California.
+ * Copyright (c) 2011-2021,  Regents of the University of California.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -22,6 +22,10 @@
 
 #include <ndn-cxx/util/ostream-joiner.hpp>
 
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
+
 #include <sstream>
 
 namespace ndn {
diff --git a/tools/peek/ndnpeek/main.cpp b/tools/peek/ndnpeek/main.cpp
index 5a8bc19..ff9f2af 100644
--- a/tools/peek/ndnpeek/main.cpp
+++ b/tools/peek/ndnpeek/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2021,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -32,6 +32,10 @@
 
 #include <ndn-cxx/util/io.hpp>
 
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
+
 #include <cerrno>
 #include <cstring>
 #include <fstream>
diff --git a/tools/peek/ndnpoke/main.cpp b/tools/peek/ndnpoke/main.cpp
index 00686ff..482cf80 100644
--- a/tools/peek/ndnpoke/main.cpp
+++ b/tools/peek/ndnpoke/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Regents of the University of California,
+ * Copyright (c) 2014-2021,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -29,6 +29,10 @@
 #include "ndnpoke.hpp"
 #include "core/version.hpp"
 
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
+
 namespace ndn {
 namespace peek {
 
diff --git a/tools/ping/client/main.cpp b/tools/ping/client/main.cpp
index 76d72ff..590c2db 100644
--- a/tools/ping/client/main.cpp
+++ b/tools/ping/client/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019,  Arizona Board of Regents.
+ * Copyright (c) 2014-2021,  Arizona Board of Regents.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -27,6 +27,11 @@
 #include "statistics-collector.hpp"
 #include "tracer.hpp"
 
+#include <boost/asio/signal_set.hpp>
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
+
 namespace ndn {
 namespace ping {
 namespace client {
diff --git a/tools/ping/client/ping.hpp b/tools/ping/client/ping.hpp
index aeab96f..48f2485 100644
--- a/tools/ping/client/ping.hpp
+++ b/tools/ping/client/ping.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2015-2019,  Arizona Board of Regents.
+ * Copyright (c) 2015-2021,  Arizona Board of Regents.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -26,6 +26,8 @@
 
 #include "core/common.hpp"
 
+#include <ndn-cxx/util/signal.hpp>
+
 namespace ndn {
 namespace ping {
 namespace client {
@@ -62,7 +64,7 @@
    * @param seq ping sequence number
    * @param rtt round trip time
    */
-  signal::Signal<Ping, uint64_t, Rtt> afterData;
+  util::Signal<Ping, uint64_t, Rtt> afterData;
 
   /**
    * @brief Signals on the return of a Nack
@@ -71,19 +73,19 @@
    * @param rtt round trip time
    * @param header the received Network NACK header
    */
-  signal::Signal<Ping, uint64_t, Rtt, lp::NackHeader> afterNack;
+  util::Signal<Ping, uint64_t, Rtt, lp::NackHeader> afterNack;
 
   /**
    * @brief Signals on timeout of a packet
    *
    * @param seq ping sequence number
    */
-  signal::Signal<Ping, uint64_t> afterTimeout;
+  util::Signal<Ping, uint64_t> afterTimeout;
 
   /**
    * @brief Signals when finished pinging
    */
-  signal::Signal<Ping> afterFinish;
+  util::Signal<Ping> afterFinish;
 
   /**
    * @brief Start sending ping interests
diff --git a/tools/ping/server/main.cpp b/tools/ping/server/main.cpp
index dcce849..d43f1d2 100644
--- a/tools/ping/server/main.cpp
+++ b/tools/ping/server/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2015-2019, Arizona Board of Regents.
+ * Copyright (c) 2015-2021, Arizona Board of Regents.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -26,6 +26,11 @@
 #include "ping-server.hpp"
 #include "tracer.hpp"
 
+#include <boost/asio/signal_set.hpp>
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
+
 namespace ndn {
 namespace ping {
 namespace server {
diff --git a/tools/ping/server/ping-server.hpp b/tools/ping/server/ping-server.hpp
index 46df6f9..f13769c 100644
--- a/tools/ping/server/ping-server.hpp
+++ b/tools/ping/server/ping-server.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2015-2019,  Arizona Board of Regents.
+ * Copyright (c) 2015-2021,  Arizona Board of Regents.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -25,6 +25,8 @@
 
 #include "core/common.hpp"
 
+#include <ndn-cxx/util/signal.hpp>
+
 namespace ndn {
 namespace ping {
 namespace server {
@@ -55,12 +57,12 @@
    *
    * @param name incoming interest name
    */
-  signal::Signal<PingServer, Name> afterReceive;
+  util::Signal<PingServer, Name> afterReceive;
 
   /**
    * @brief Signals when finished pinging
    */
-  signal::Signal<PingServer> afterFinish;
+  util::Signal<PingServer> afterFinish;
 
   /** @brief starts ping server
    *