30.1 Generic support for TCP

ns-3 was written to support multiple TCP implementations. The implementations inherit from a few common header classes in the src/node directory, so that user code can swap out implementations with minimal changes to the scripts.

There are two important abstract base classes:

• class TcpSocket: This is defined in src/node/tcp-socket.{cc,h}. This class exists for hosting TcpSocket attributes that can be reused across different implementations. For instance, TcpSocket::SetInitialCwnd() can be used for any of the implementations that derive from class TcpSocket.
• class TcpSocketFactory: This is used by applications to create TCP sockets. A typical usage can be seen in this snippet:

    // Create the socket if not already created
    if (!m_socket)
      {
        m_socket = Socket::CreateSocket (GetNode(), m_tid);
        m_socket->Bind (m_local);
        ...
      }
  

  The parameter m_tid controls the TypeId of the actual TCP Socket implementation that is instantiated. This way, the application can be written generically and different socket implementations can be swapped out by specifying the TypeId.

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