diff --git a/model/ccnx-face.h b/model/ccnx-face.h
index 8bae198..1119ba8 100644
--- a/model/ccnx-face.h
+++ b/model/ccnx-face.h
@@ -208,6 +208,14 @@
    *
    * Internal index is used for comparison.
    */
+  inline bool
+  operator!= (const CcnxFace &face) const;
+  
+  /**
+   * \brief Compare two faces. Only two faces on the same node could be compared.
+   *
+   * Internal index is used for comparison.
+   */
   bool
   operator< (const CcnxFace &face) const;
 
@@ -266,6 +274,13 @@
   return m_id;
 }
 
+inline bool
+CcnxFace::operator!= (const CcnxFace &face) const
+{
+  return !(*this == face);
+}
+
+
 } // namespace ns3
 
 #endif //CCNX_FACE_H