Added box for figure

3-environment.tex

@@ -20,7 +20,7 @@ It provides a lightweight messaging mechanism implementing the publish-subscribe
 The controller software has out-of-the-box support for this protocol, which allows easy integration of all different device types using the same patterns.
 
 \begin{figure}[htbp]
-\centering\includegraphics[width=0.4\textwidth]{topology.pdf}
+\centering\fbox{\includegraphics[width=0.4\textwidth]{topology.pdf}}
 \caption{The base network topology.}
 \label{fig:topology}
 \end{figure}