diff --git a/src/diff-state-container.cpp b/src/diff-state-container.cpp
new file mode 100644
index 0000000..38a67f3
--- /dev/null
+++ b/src/diff-state-container.cpp
@@ -0,0 +1,25 @@
+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012-2014 University of California, Los Angeles
+ *
+ * This file is part of ChronoSync, synchronization library for distributed realtime
+ * applications for NDN.
+ *
+ * ChronoSync 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.
+ *
+ * ChronoSync 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
+ * ChronoSync, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @author Zhenkai Zhu <http://irl.cs.ucla.edu/~zhenkai/>
+ * @author Chaoyi Bian <bcy@pku.edu.cn>
+ * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
+ * @author Yingdi Yu <yingdi@cs.ucla.edu>
+ */
+
+#include "diff-state-container.hpp"
diff --git a/src/sync-diff-state-container.h b/src/diff-state-container.hpp
similarity index 71%
rename from src/sync-diff-state-container.h
rename to src/diff-state-container.hpp
index 428877e..d20fbee 100644
--- a/src/sync-diff-state-container.h
+++ b/src/diff-state-container.hpp
@@ -19,35 +19,47 @@
  * @author Zhenkai Zhu <http://irl.cs.ucla.edu/~zhenkai/>
  * @author Chaoyi Bian <bcy@pku.edu.cn>
  * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
+ * @author Yingdi Yu <yingdi@cs.ucla.edu>
  */
 
-#ifndef SYNC_DIFF_STATE_CONTAINER_H
-#define SYNC_DIFF_STATE_CONTAINER_H
+#ifndef CHRONOSYNC_DIFF_STATE_CONTAINER_HPP
+#define CHRONOSYNC_DIFF_STATE_CONTAINER_HPP
 
-#include "sync-diff-state.h"
-#include "sync-digest.h"
+#include "mi-tag.hpp"
+#include "diff-state.hpp"
 
 #include <boost/multi_index_container.hpp>
 #include <boost/multi_index/tag.hpp>
-// #include <boost/multi_index/ordered_index.hpp>
-// #include <boost/multi_index/composite_key.hpp>
 #include <boost/multi_index/hashed_index.hpp>
 #include <boost/multi_index/sequenced_index.hpp>
-// #include <boost/multi_index/random_access_index.hpp>
 #include <boost/multi_index/member.hpp>
 #include <boost/multi_index/mem_fun.hpp>
 
+namespace chronosync {
+
 namespace mi = boost::multi_index;
 
-namespace Sync {
+struct DigestPtrHash
+{
+  std::size_t
+  operator()(ndn::ConstBufferPtr digest) const
+  {
+    BOOST_ASSERT(digest->size() > sizeof(std::size_t));
 
-/// @cond include_hidden
-struct sequenced { };
-struct timed { };
-/// @endcond
+    return *reinterpret_cast<const std::size_t*>(digest->buf());
+  }
+};
+
+struct DigestPtrEqual
+{
+  bool
+  operator()(ndn::ConstBufferPtr digest1, ndn::ConstBufferPtr digest2) const
+  {
+    return *digest1 == *digest2;
+  }
+};
 
 /**
- * \ingroup sync
  * @brief Container for differential states
  */
 struct DiffStateContainer : public mi::multi_index_container<
@@ -56,11 +68,11 @@ struct DiffStateContainer : public mi::multi_index_container<
     // For fast access to elements using DiffState hashes
     mi::hashed_unique<
       mi::tag<hashed>,
-      mi::const_mem_fun<DiffState, DigestConstPtr, &DiffState::getDigest>,
+      mi::const_mem_fun<DiffState, ndn::ConstBufferPtr, &DiffState::getRootDigest>,
       DigestPtrHash,
       DigestPtrEqual
-      >
-    ,
+      >,
+
     // sequenced index to access older/newer element (like in list)
     mi::sequenced<mi::tag<sequenced> >
     >
@@ -68,6 +80,6 @@ struct DiffStateContainer : public mi::multi_index_container<
 {
 };
 
-} // Sync
+} // namespace chronosync
 
-#endif // SYNC_DIFF_STATE_CONTAINER_H
+#endif // CHRONOSYNC_DIFF_STATE_CONTAINER_HPP
diff --git a/src/diff-state.cpp b/src/diff-state.cpp
new file mode 100644
index 0000000..f5813bf
--- /dev/null
+++ b/src/diff-state.cpp
@@ -0,0 +1,43 @@
+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012-2014 University of California, Los Angeles
+ *
+ * This file is part of ChronoSync, synchronization library for distributed realtime
+ * applications for NDN.
+ *
+ * ChronoSync 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.
+ *
+ * ChronoSync 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
+ * ChronoSync, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @author Zhenkai Zhu <http://irl.cs.ucla.edu/~zhenkai/>
+ * @author Chaoyi Bian <bcy@pku.edu.cn>
+ * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
+ * @author Yingdi Yu <yingdi@cs.ucla.edu>
+ */
+
+#include "diff-state.hpp"
+
+namespace chronosync {
+
+ConstStatePtr
+DiffState::diff() const
+{
+  StatePtr result = make_shared<State>();
+
+  ConstDiffStatePtr state = m_next;
+  while (static_cast<bool>(state)) {
+    *result += *state;
+    state = state->m_next;
+  }
+
+  return result;
+}
+
+} // namespace chronosync
diff --git a/src/diff-state.hpp b/src/diff-state.hpp
new file mode 100644
index 0000000..46ed412
--- /dev/null
+++ b/src/diff-state.hpp
@@ -0,0 +1,104 @@
+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012-2014 University of California, Los Angeles
+ *
+ * This file is part of ChronoSync, synchronization library for distributed realtime
+ * applications for NDN.
+ *
+ * ChronoSync 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.
+ *
+ * ChronoSync 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
+ * ChronoSync, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @author Zhenkai Zhu <http://irl.cs.ucla.edu/~zhenkai/>
+ * @author Chaoyi Bian <bcy@pku.edu.cn>
+ * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
+ * @author Yingdi Yu <yingdi@cs.ucla.edu>
+ */
+
+#ifndef CHRONOSYNC_DIFF_STATE_HPP
+#define CHRONOSYNC_DIFF_STATE_HPP
+
+#include "state.hpp"
+
+namespace chronosync {
+
+class DiffState;
+typedef shared_ptr<DiffState> DiffStatePtr;
+typedef shared_ptr<const DiffState> ConstDiffStatePtr;
+
+/**
+ * @brief Contains the diff info between two states.
+ *
+ * DiffState is used to construct DiffLog.  It serves as
+ * a log entry.  Each log entry contains the updates between
+ * two states, and is indexed by the digest of the second state
+ * which is the result when the updates have been applied.
+ *
+ * DiffLog is a chain of DiffStates. Each DiffState connects to
+ * the next DiffState (a newer diff) through member m_next. The
+ * m_next of the last DiffState in a log should be empty. And the
+ * root digest of the last DiffState in the log should be the most
+ * current state.
+ */
+class DiffState : public State
+{
+public:
+  /**
+   * @brief Set successor for the diff state
+   *
+   * @param next successor state
+   */
+  void
+  setNext(ConstDiffStatePtr next)
+  {
+    m_next = next;
+  }
+
+  /**
+   * @brief Set digest for the diff state (obtained from a corresponding full state)
+   *
+   * @param digest root digest of the full state
+   */
+  void
+  setRootDigest(ndn::ConstBufferPtr digest)
+  {
+    m_digest = digest;
+  }
+
+  /**
+   * @brief Get root digest of the full state after applying the diff state
+   */
+  ndn::ConstBufferPtr
+  getRootDigest() const
+  {
+    return m_digest;
+  }
+
+  /**
+   * @brief Accumulate differences from this state to the most current state
+   *
+   * This method assumes that the DiffState is in a log. It will iterate the all
+   * the DiffState between its m_next DiffState and the last DiffState in the log,
+   * and aggregate all the differences into one diff, which is represented as a
+   * State object.
+   *
+   * @returns Accumulated differences from this state to the most current state
+   */
+  ConstStatePtr
+  diff() const;
+
+private:
+  ConstDiffStatePtr   m_next;
+  ndn::ConstBufferPtr m_digest;
+};
+
+} // chronosync
+
+#endif // CHRONOSYNC_DIFF_STATE_HPP
diff --git a/src/sync-diff-state.cc b/src/sync-diff-state.cc
deleted file mode 100644
index 5ddaace..0000000
--- a/src/sync-diff-state.cc
+++ /dev/null
@@ -1,102 +0,0 @@
-/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
-/*
- * Copyright (c) 2012-2014 University of California, Los Angeles
- *
- * This file is part of ChronoSync, synchronization library for distributed realtime
- * applications for NDN.
- *
- * ChronoSync 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.
- *
- * ChronoSync 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
- * ChronoSync, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
- *
- * @author Zhenkai Zhu <http://irl.cs.ucla.edu/~zhenkai/>
- * @author Chaoyi Bian <bcy@pku.edu.cn>
- * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
- */
-
-#include "sync-diff-state.h"
-#include "sync-diff-leaf.h"
-
-#include <boost/make_shared.hpp>
-#include <boost/foreach.hpp>
-#include <boost/assert.hpp>
-
-using namespace boost;
-
-namespace Sync {
-
-DiffState::DiffState ()
-{
-}
-
-DiffState::~DiffState ()
-{
-}
-
-DiffStatePtr
-DiffState::diff () const
-{
-  DiffStatePtr ret = make_shared<DiffState> ();
-
-  DiffStatePtr state = m_next;
-  while (state != 0)
-    {
-      *ret += *state;
-      state = state->m_next;
-    }
-
-  return ret;
-}
-
-DiffState &
-DiffState::operator += (const DiffState &state)
-{
-  BOOST_FOREACH (LeafConstPtr _leaf, state.getLeaves ())
-    {
-      DiffLeafConstPtr leaf = dynamic_pointer_cast<const DiffLeaf> (_leaf);
-      BOOST_ASSERT (leaf != 0);
-
-      if (leaf->getOperation () == UPDATE)
-        update (leaf->getInfo (), leaf->getSeq ());
-      else if (leaf->getOperation () == REMOVE)
-        remove (leaf->getInfo ());
-      else
-        {
-          BOOST_ASSERT (false);
-        }
-    }
-
-  return *this;
-}
-
-// from State
-boost::tuple<bool/*inserted*/, bool/*updated*/, SeqNo/*oldSeqNo*/>
-DiffState::update (NameInfoConstPtr info, const SeqNo &seq)
-{
-  m_leaves.erase (info);
-
-  DiffLeafPtr leaf = make_shared<DiffLeaf> (info, cref (seq));
-  m_leaves.insert (leaf);
-
-  return make_tuple (true, false, SeqNo ());
-}
-
-bool
-DiffState::remove (NameInfoConstPtr info)
-{
-  m_leaves.erase (info);
-
-  DiffLeafPtr leaf = make_shared<DiffLeaf> (info);
-  m_leaves.insert (leaf);
-
-  return true;
-}
-
-} // ns3
diff --git a/src/sync-diff-state.h b/src/sync-diff-state.h
deleted file mode 100644
index da0d649..0000000
--- a/src/sync-diff-state.h
+++ /dev/null
@@ -1,103 +0,0 @@
-/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
-/*
- * Copyright (c) 2012-2014 University of California, Los Angeles
- *
- * This file is part of ChronoSync, synchronization library for distributed realtime
- * applications for NDN.
- *
- * ChronoSync 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.
- *
- * ChronoSync 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
- * ChronoSync, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
- *
- * @author Zhenkai Zhu <http://irl.cs.ucla.edu/~zhenkai/>
- * @author Chaoyi Bian <bcy@pku.edu.cn>
- * @author Alexander Afanasyev <http://lasr.cs.ucla.edu/afanasyev/index.html>
- */
-
-#ifndef SYNC_DIFF_STATE_H
-#define SYNC_DIFF_STATE_H
-
-#include "sync-state.h"
-#include <iostream>
-
-namespace Sync {
-
-class DiffState;
-typedef boost::shared_ptr<DiffState> DiffStatePtr;
-typedef boost::shared_ptr<DiffState> DiffStateConstPtr;
-
-/**
- * @ingroup ccnx
- * @brief Differential SYNC state
- */
-class DiffState : public State
-{
-public:
-  /**
-   * @see Default constructor
-   */
-  DiffState ();
-  virtual ~DiffState ();
-
-  /**
-   * @brief Set successor for the diff state
-   * @param next successor state
-   */
-  void
-  setNext (DiffStatePtr next)
-  {
-    m_next = next;
-  }
-
-  /**
-   * @brief Set digest for the diff state (obtained from a corresponding full state)
-   * @param digest A read only smart pointer to a digest object (that should be unmodified anywhere else)
-   */
-  void
-  setDigest (DigestConstPtr digest) { m_digest = digest; }
-
-  /**
-   * @brief Get digest for the diff state
-   */
-  DigestConstPtr
-  getDigest () const { return m_digest; }
-
-  /**
-   * @brief Accumulate differences from `this' state to the most current state
-   * @returns Accumulated differences from `this' state to the most current state
-   */
-  DiffStatePtr
-  diff () const;
-
-  /**
-   * @brief Combine differences from `this' and `state'
-   * @param state Differential state to combine with
-   * @return Combined differences
-   *
-   * In case of collisions, `this' leaf will be replaced with the leaf of `state'
-   */
-  DiffState&
-  operator += (const DiffState &state);
-
-  // from State
-  virtual boost::tuple<bool/*inserted*/, bool/*updated*/, SeqNo/*oldSeqNo*/>
-  update (NameInfoConstPtr info, const SeqNo &seq);
-
-  virtual bool
-  remove (NameInfoConstPtr info);
-
-private:
-  DiffStatePtr m_next;
-  DigestConstPtr m_digest;
-};
-
-} // Sync
-
-#endif // SYNC_DIFF_STATE_H
diff --git a/tests/unit-tests/test-diff-state.cpp b/tests/unit-tests/test-diff-state.cpp
new file mode 100644
index 0000000..a4b740f
--- /dev/null
+++ b/tests/unit-tests/test-diff-state.cpp
@@ -0,0 +1,140 @@
+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012-2014 University of California, Los Angeles
+ *
+ * This file is part of ChronoSync, synchronization library for distributed realtime
+ * applications for NDN.
+ *
+ * ChronoSync 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.
+ *
+ * ChronoSync 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
+ * ChronoSync, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "diff-state.hpp"
+#include "diff-state-container.hpp"
+#include "boost-test.hpp"
+
+namespace chronosync {
+namespace test {
+
+BOOST_AUTO_TEST_SUITE(DiffStateTests)
+
+BOOST_AUTO_TEST_CASE(Diff)
+{
+  State state;
+
+  Name info1("/test/name");
+  info1.appendNumber(0);
+
+  Name info2("/test/name");
+  info2.appendNumber(1);
+
+  Name info3("/test/name");
+  info3.appendNumber(2);
+
+  DiffStatePtr root = make_shared<DiffState>();
+  DiffStatePtr action1 = make_shared<DiffState>();
+  root->setNext(action1);
+
+  state.update(info1, 1);
+  action1->update(info1, 1);
+  action1->setRootDigest(state.getRootDigest());
+
+  DiffStatePtr action2 = make_shared<DiffState>();
+  action1->setNext(action2);
+
+  state.update(info2, 1);
+  state.update(info3, 2);
+  action2->update(info2, 1);
+  action2->update(info3, 2);
+  action2->setRootDigest(state.getRootDigest());
+
+  LeafContainer::index<ordered>::type::iterator it;
+  ConstStatePtr diff0 = root->diff();
+  BOOST_CHECK_EQUAL(diff0->getLeaves().size(), 3);
+  it = diff0->getLeaves().get<ordered>().begin();
+  BOOST_CHECK_EQUAL((*it)->getSessionName(), info1);
+  BOOST_CHECK_EQUAL((*it)->getSeq(), 1);
+  it++;
+  BOOST_CHECK_EQUAL((*it)->getSessionName(), info2);
+  BOOST_CHECK_EQUAL((*it)->getSeq(), 1);
+  it++;
+  BOOST_CHECK_EQUAL((*it)->getSessionName(), info3);
+  BOOST_CHECK_EQUAL((*it)->getSeq(), 2);
+
+  ConstStatePtr diff1 = action1->diff();
+  BOOST_CHECK_EQUAL(diff1->getLeaves().size(), 2);
+  it = diff1->getLeaves().get<ordered>().begin();
+  BOOST_CHECK_EQUAL((*it)->getSessionName(), info2);
+  BOOST_CHECK_EQUAL((*it)->getSeq(), 1);
+  it++;
+  BOOST_CHECK_EQUAL((*it)->getSessionName(), info3);
+  BOOST_CHECK_EQUAL((*it)->getSeq(), 2);
+}
+
+BOOST_AUTO_TEST_CASE(Container)
+{
+  DiffStateContainer container;
+
+  State state;
+
+  Name info1("/test/name");
+  info1.appendNumber(0);
+
+  Name info2("/test/name");
+  info2.appendNumber(1);
+
+  Name info3("/test/name");
+  info3.appendNumber(2);
+
+  DiffStatePtr root = make_shared<DiffState>();
+  DiffStatePtr action1 = make_shared<DiffState>();
+  root->setNext(action1);
+
+  state.update(info1, 1);
+  action1->update(info1, 1);
+  ndn::ConstBufferPtr digest1 = state.getRootDigest();
+  action1->setRootDigest(digest1);
+
+  DiffStatePtr action2 = make_shared<DiffState>();
+  action1->setNext(action2);
+
+  state.update(info2, 1);
+  state.update(info3, 2);
+  action2->update(info2, 1);
+  action2->update(info3, 2);
+  ndn::ConstBufferPtr digest2 = state.getRootDigest();
+  action2->setRootDigest(digest2);
+
+  DiffStatePtr action3 = make_shared<DiffState>();
+  state.update(info1, 3);
+  state.update(info3, 4);
+  action3->update(info1, 3);
+  action3->update(info3, 4);
+  ndn::ConstBufferPtr digest3 = state.getRootDigest();
+  action3->setRootDigest(digest3);
+
+  container.insert(action3);
+  container.insert(action2);
+  container.insert(action1);
+  BOOST_CHECK_EQUAL(container.size(), 3);
+
+  DiffStateContainer::index<sequenced>::type::iterator it = container.get<sequenced>().begin();
+  BOOST_CHECK(*(*it)->getRootDigest() == *digest3);
+  it++;
+  BOOST_CHECK(*(*it)->getRootDigest() == *digest2);
+  it++;
+  BOOST_CHECK(*(*it)->getRootDigest() == *digest1);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+} // namespace test
+} // namespace chronosync