diff --git a/apps/ndn-app.hpp b/apps/ndn-app.hpp
index 7d335b3..8ba90d3 100644
--- a/apps/ndn-app.hpp
+++ b/apps/ndn-app.hpp
@@ -80,6 +80,10 @@
   virtual void
   OnData(shared_ptr<const Data> data);
 
+public:
+  typedef void (*InterestTraceCallback)(shared_ptr<const Interest>, Ptr<App>, shared_ptr<Face>);
+  typedef void (*DataTraceCallback)(shared_ptr<const Data>, Ptr<App>, shared_ptr<Face>);
+
 protected:
   /**
    * @brief Do cleanup when application is destroyed