diff --git a/model/sync-diff-state.h b/model/sync-diff-state.h
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+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Zhenkai Zhu <zhenkai@cs.ucla.edu>
+ *         卞超轶 Chaoyi Bian <bcy@pku.edu.cn>
+ *	   Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ */
+
+#ifndef SYNC_DIFF_STATE_H
+#define SYNC_DIFF_STATE_H
+
+#include "sync-state.h"
+
+namespace ns3 {
+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;
+  }
+
+  // void
+  // setDigest (Hash digest);
+
+  // Hash
+  // getDigest () const;
+
+  /**
+   * @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 void
+  update (NameInfoConstPtr info, const SeqNo &seq);
+
+  virtual void
+  remove (NameInfoConstPtr info);
+  
+private:
+  DiffStatePtr m_next;
+  // Hash m_digest;
+};
+
+} // Sync
+} // ns3
+
+#endif // SYNC_DIFF_STATE_H