Update README and add contrib dir

contrib/ethernet/model/switch-channel.h

@@ -0,0 +1,59 @@
+#ifndef SWITCH_CHANNEL_H
+#define SWITCH_CHANNEL_H
+
+#include "ns3/channel.h"
+#include "ns3/net-device.h"
+
+#include <vector>
+
+/**
+ * \file
+ * \ingroup ethernet
+ * ns3::SwitchChannel declaration.
+ */
+
+namespace ns3
+{
+
+/**
+ * \ingroup bridge
+ *
+ * \brief Virtual channel implementation for bridges (BridgeNetDevice).
+ *
+ * Just like SwitchNetDevice aggregates multiple NetDevices,
+ * SwitchChannel aggregates multiple channels and make them appear as
+ * a single channel to upper layers.
+ * This class is greatly inspire form BridgeChannel
+ */
+class SwitchChannel : public Channel
+{
+  public:
+    /**
+     * \brief Get the type ID.
+     * \return the object TypeId
+     */
+    static TypeId GetTypeId();
+    SwitchChannel();
+    ~SwitchChannel() override;
+
+    // Delete copy constructor and assignment operator to avoid misuse
+    SwitchChannel(const SwitchChannel&) = delete;
+    SwitchChannel& operator=(const SwitchChannel&) = delete;
+
+    /**
+     * Adds a channel to the bridged pool
+     * \param bridgedChannel  the channel to add to the pool
+     */
+    void AddChannel(Ptr<Channel> bridgedChannel);
+
+    // virtual methods implementation, from Channel
+    std::size_t GetNDevices() const override;
+    Ptr<NetDevice> GetDevice(std::size_t i) const override;
+
+  private:
+    std::vector<Ptr<Channel>> m_switchedChannels; //!< pool of switched channels
+};
+
+} // namespace ns3
+
+#endif /* SWITCH_CHANNEL_H */