Update README and add contrib dir

contrib/tsn/model/clock.h

@@ -0,0 +1,70 @@
+#ifndef CLOCK_H
+#define CLOCK_H
+
+#include "ns3/object.h"
+#include "ns3/nstime.h"
+
+namespace ns3
+{
+
+class Clock: public Object
+{
+  public:
+    /**
+     * \brief Get the TypeId
+     *
+     * \return The TypeId for this class
+     */
+    static TypeId GetTypeId();
+
+    /**
+     * \brief Create a Clock
+     */
+    Clock();
+
+    /**
+     * Destroy a Clock
+     *
+     * This is the destructor for the Clock.
+     */
+    ~Clock();
+
+    // Delete copy constructor and assignment operator to avoid misuse
+    Clock& operator=(const Clock&) = delete;
+    Clock(const Clock&) = delete;
+
+    void AddClockCorrectionCallback(Callback<void> cb);
+    void TriggerCorrectionCallback();
+
+    virtual Time GetLocalTime();
+    virtual Time GetUncorrectedLocalTime();
+    /**
+    *
+    * \brief Get Clock time at instant t in the simulator/perfect time base
+    *
+    * \params t Timestamp in the simulator/perfect time base
+    * \return clock time at instant t
+    */
+    virtual Time GetTimeAt(Time t);
+    /**
+    *
+    * \brief Get duration in the clock timebase from duration in the simulator/perfect time base
+    *
+    * \params d duration in the simulator/perfect time base
+    * \return duration in the clock timebase
+    */
+    virtual Time GetDuration(Time d);
+    virtual void UpdateTime();
+    void SetOffsetTime(Time offset);
+
+  protected:
+    Time m_correctionOffset = Time(0);
+    Time m_granularity;
+  private:
+
+    std::vector<Callback<void>> m_callbacks;
+
+};
+
+}
+#endif /* CLOCK_H */