Update README and add contrib dir

contrib/tsn/model/transmission-gate.h

@@ -0,0 +1,63 @@
+#ifndef TRANSMISSION_GATE_H
+#define TRANSMISSION_GATE_H
+
+#include "ns3/object.h"
+#include "ns3/packet.h"
+
+namespace ns3
+{
+
+class TransmissionGate: public Object
+{
+  public:
+    /**
+     * \brief Get the TypeId
+     *
+     * \return The TypeId for this class
+     */
+    static TypeId GetTypeId();
+
+    /**
+     * \brief Create a TransmissionGate
+     */
+    TransmissionGate();
+
+    /**
+     * Destroy a TransmissionGate
+     *
+     * This is the destructor for the TransmissionGate.
+     */
+    ~TransmissionGate();
+
+    // Delete copy constructor and assignment operator to avoid misuse
+    TransmissionGate& operator=(const TransmissionGate&) = delete;
+    TransmissionGate(const TransmissionGate&) = delete;
+
+    bool IsOpen();
+    void Open();
+    void Close();
+
+  protected:
+
+  private:
+    /**
+     * Enumeration of the states of the transimission gate.
+     */
+    enum State
+    {
+        OPEN, /**< The transimission gate is open */
+        CLOSE /**< The transimission gate is close */
+    };
+
+    /**
+     * The state of the Net Device transmit state machine.
+     */
+    State m_state;
+
+};
+
+}
+
+
+
+#endif /* TRANSMISSION_GATE_H */